/* eslint-env mocha */
const chai = require('chai')
const testDb = 'workspace/test.db'
const fs = require('fs')
const path = require('path')
const { apply, each, waterfall } = require('./utils.test.js')
const model = require('../lib/model')
const Datastore = require('../lib/datastore')
const Persistence = require('../lib/persistence')
const { callbackify } = require('util')
const reloadTimeUpperBound = 200 // In ms, an upper bound for the reload time used to check createdAt and updatedAt

const { assert } = chai
chai.should()

describe('Database', function () {
  let d

  beforeEach(function (done) {
    d = new Datastore({ filename: testDb })
    d.filename.should.equal(testDb)
    d.inMemoryOnly.should.equal(false)

    waterfall([
      function (cb) {
        callbackify((dirname) => Persistence.ensureDirectoryExistsAsync(dirname))(path.dirname(testDb), function () {
          fs.access(testDb, fs.constants.FS_OK, function (err) {
            if (!err) {
              fs.unlink(testDb, cb)
            } else { return cb() }
          })
        })
      },
      function (cb) {
        d.loadDatabase(function (err) {
          assert.isNull(err)
          d.getAllData().length.should.equal(0)
          return cb()
        })
      }
    ], done)
  })

  it('Constructor compatibility with v0.6-', function () {
    let dbef = new Datastore('somefile')
    dbef.filename.should.equal('somefile')
    dbef.inMemoryOnly.should.equal(false)

    dbef = new Datastore('')
    assert.isNull(dbef.filename)
    dbef.inMemoryOnly.should.equal(true)

    dbef = new Datastore()
    assert.isNull(dbef.filename)
    dbef.inMemoryOnly.should.equal(true)
  })

  describe('Autoloading', function () {
    it('Can autoload a database and query it right away', function (done) {
      const fileStr = model.serialize({ _id: '1', a: 5, planet: 'Earth' }) + '\n' + model.serialize({
        _id: '2',
        a: 5,
        planet: 'Mars'
      }) + '\n'
      const autoDb = 'workspace/auto.db'

      fs.writeFileSync(autoDb, fileStr, 'utf8')
      const db = new Datastore({ filename: autoDb, autoload: true })

      db.find({}, function (err, docs) {
        assert.isNull(err)
        docs.length.should.equal(2)
        done()
      })
    })

    it('Throws if autoload fails', function (done) {
      const fileStr = model.serialize({ _id: '1', a: 5, planet: 'Earth' }) + '\n' + model.serialize({
        _id: '2',
        a: 5,
        planet: 'Mars'
      }) + '\n' + '{"$$indexCreated":{"fieldName":"a","unique":true}}'
      const autoDb = 'workspace/auto.db'

      fs.writeFileSync(autoDb, fileStr, 'utf8')

      // Check the loadDatabase generated an error
      function onload (err) {
        err.errorType.should.equal('uniqueViolated')
        done()
      }

      const db = new Datastore({ filename: autoDb, autoload: true, onload: onload })

      // eslint-disable-next-line node/handle-callback-err
      db.find({}, function (err, docs) {
        done(new Error('Find should not be executed since autoload failed'))
      })
    })
  })

  describe('Insert', function () {
    it('Able to insert a document in the database, setting an _id if none provided, and retrieve it even after a reload', function (done) {
      // eslint-disable-next-line node/handle-callback-err
      d.find({}, function (err, docs) {
        docs.length.should.equal(0)

        // eslint-disable-next-line node/handle-callback-err
        d.insert({ somedata: 'ok' }, function (err) {
          // The data was correctly updated
          d.find({}, function (err, docs) {
            assert.isNull(err)
            docs.length.should.equal(1)
            Object.keys(docs[0]).length.should.equal(2)
            docs[0].somedata.should.equal('ok')
            assert.isDefined(docs[0]._id)

            // After a reload the data has been correctly persisted
            // eslint-disable-next-line node/handle-callback-err
            d.loadDatabase(function (err) {
              d.find({}, function (err, docs) {
                assert.isNull(err)
                docs.length.should.equal(1)
                Object.keys(docs[0]).length.should.equal(2)
                docs[0].somedata.should.equal('ok')
                assert.isDefined(docs[0]._id)

                done()
              })
            })
          })
        })
      })
    })

    it('Can insert multiple documents in the database', function (done) {
      // eslint-disable-next-line node/handle-callback-err
      d.find({}, function (err, docs) {
        docs.length.should.equal(0)

        // eslint-disable-next-line node/handle-callback-err
        d.insert({ somedata: 'ok' }, function (err) {
          // eslint-disable-next-line node/handle-callback-err
          d.insert({ somedata: 'another' }, function (err) {
            // eslint-disable-next-line node/handle-callback-err
            d.insert({ somedata: 'again' }, function (err) {
              // eslint-disable-next-line node/handle-callback-err
              d.find({}, function (err, docs) {
                docs.length.should.equal(3)
                docs.map(x => x.somedata).should.contain('ok')
                docs.map(x => x.somedata).should.contain('another')
                docs.map(x => x.somedata).should.contain('again')
                done()
              })
            })
          })
        })
      })
    })

    it('Can insert and get back from DB complex objects with all primitive and secondary types', function (done) {
      const da = new Date()
      const obj = { a: ['ee', 'ff', 42], date: da, subobj: { a: 'b', b: 'c' } }

      // eslint-disable-next-line node/handle-callback-err
      d.insert(obj, function (err) {
        d.findOne({}, function (err, res) {
          assert.isNull(err)
          res.a.length.should.equal(3)
          res.a[0].should.equal('ee')
          res.a[1].should.equal('ff')
          res.a[2].should.equal(42)
          res.date.getTime().should.equal(da.getTime())
          res.subobj.a.should.equal('b')
          res.subobj.b.should.equal('c')

          done()
        })
      })
    })

    it('If an object returned from the DB is modified and refetched, the original value should be found', function (done) {
      d.insert({ a: 'something' }, function () {
        // eslint-disable-next-line node/handle-callback-err
        d.findOne({}, function (err, doc) {
          doc.a.should.equal('something')
          doc.a = 'another thing'
          doc.a.should.equal('another thing')

          // Re-fetching with findOne should yield the persisted value
          // eslint-disable-next-line node/handle-callback-err
          d.findOne({}, function (err, doc) {
            doc.a.should.equal('something')
            doc.a = 'another thing'
            doc.a.should.equal('another thing')

            // Re-fetching with find should yield the persisted value
            // eslint-disable-next-line node/handle-callback-err
            d.find({}, function (err, docs) {
              docs[0].a.should.equal('something')

              done()
            })
          })
        })
      })
    })

    it('Cannot insert a doc that has a field beginning with a $ sign', function (done) {
      d.insert({ $something: 'atest' }, function (err) {
        assert.isDefined(err)
        done()
      })
    })

    it('If an _id is already given when we insert a document, use that instead of generating a random one', function (done) {
      d.insert({ _id: 'test', stuff: true }, function (err, newDoc) {
        if (err) { return done(err) }

        newDoc.stuff.should.equal(true)
        newDoc._id.should.equal('test')

        d.insert({ _id: 'test', otherstuff: 42 }, function (err) {
          err.errorType.should.equal('uniqueViolated')

          done()
        })
      })
    })

    it('Modifying the insertedDoc after an insert doesnt change the copy saved in the database', function (done) {
      // eslint-disable-next-line node/handle-callback-err
      d.insert({ a: 2, hello: 'world' }, function (err, newDoc) {
        newDoc.hello = 'changed'

        // eslint-disable-next-line node/handle-callback-err
        d.findOne({ a: 2 }, function (err, doc) {
          doc.hello.should.equal('world')
          done()
        })
      })
    })

    it('Can insert an array of documents at once', function (done) {
      const docs = [{ a: 5, b: 'hello' }, { a: 42, b: 'world' }]

      // eslint-disable-next-line node/handle-callback-err
      d.insert(docs, function (err) {
        // eslint-disable-next-line node/handle-callback-err
        d.find({}, function (err, docs) {
          docs.length.should.equal(2)
          docs.find(function (doc) { return doc.a === 5 }).b.should.equal('hello')
          docs.find(function (doc) { return doc.a === 42 }).b.should.equal('world')

          // The data has been persisted correctly
          const data = fs.readFileSync(testDb, 'utf8').split('\n').filter(function (line) { return line.length > 0 })
          data.length.should.equal(2)
          model.deserialize(data[0]).a.should.equal(5)
          model.deserialize(data[0]).b.should.equal('hello')
          model.deserialize(data[1]).a.should.equal(42)
          model.deserialize(data[1]).b.should.equal('world')

          done()
        })
      })
    })

    it('If a bulk insert violates a constraint, all changes are rolled back', function (done) {
      const docs = [{ a: 5, b: 'hello' }, { a: 42, b: 'world' }, { a: 5, b: 'bloup' }, { a: 7 }]

      d.ensureIndex({ fieldName: 'a', unique: true }, function () { // Important to specify callback here to make sure filesystem synced
        d.insert(docs, function (err) {
          err.errorType.should.equal('uniqueViolated')

          // eslint-disable-next-line node/handle-callback-err
          d.find({}, function (err, docs) {
            // Datafile only contains index definition
            const datafileContents = model.deserialize(fs.readFileSync(testDb, 'utf8'))
            assert.deepStrictEqual(datafileContents, { $$indexCreated: { fieldName: 'a', unique: true } })

            docs.length.should.equal(0)

            done()
          })
        })
      })
    })

    it('If timestampData option is set, a createdAt field is added and persisted', function (done) {
      const newDoc = { hello: 'world' }; const beginning = Date.now()
      d = new Datastore({ filename: testDb, timestampData: true, autoload: true })
      d.find({}, function (err, docs) {
        assert.isNull(err)
        docs.length.should.equal(0)

        // eslint-disable-next-line node/handle-callback-err
        d.insert(newDoc, function (err, insertedDoc) {
          // No side effect on given input
          assert.deepStrictEqual(newDoc, { hello: 'world' })
          // Insert doc has two new fields, _id and createdAt
          insertedDoc.hello.should.equal('world')
          assert.isDefined(insertedDoc.createdAt)
          assert.isDefined(insertedDoc.updatedAt)
          insertedDoc.createdAt.should.equal(insertedDoc.updatedAt)
          assert.isDefined(insertedDoc._id)
          Object.keys(insertedDoc).length.should.equal(4)
          assert.isBelow(Math.abs(insertedDoc.createdAt.getTime() - beginning), reloadTimeUpperBound) // No more than 30ms should have elapsed (worst case, if there is a flush)

          // Modifying results of insert doesn't change the cache
          insertedDoc.bloup = 'another'
          Object.keys(insertedDoc).length.should.equal(5)

          // eslint-disable-next-line node/handle-callback-err
          d.find({}, function (err, docs) {
            docs.length.should.equal(1)
            assert.deepStrictEqual(newDoc, { hello: 'world' })
            assert.deepStrictEqual({
              hello: 'world',
              _id: insertedDoc._id,
              createdAt: insertedDoc.createdAt,
              updatedAt: insertedDoc.updatedAt
            }, docs[0])

            // All data correctly persisted on disk
            d.loadDatabase(function () {
              // eslint-disable-next-line node/handle-callback-err
              d.find({}, function (err, docs) {
                docs.length.should.equal(1)
                assert.deepStrictEqual(newDoc, { hello: 'world' })
                assert.deepStrictEqual({
                  hello: 'world',
                  _id: insertedDoc._id,
                  createdAt: insertedDoc.createdAt,
                  updatedAt: insertedDoc.updatedAt
                }, docs[0])

                done()
              })
            })
          })
        })
      })
    })

    it('If timestampData option not set, don\'t create a createdAt and a updatedAt field', function (done) {
      // eslint-disable-next-line node/handle-callback-err
      d.insert({ hello: 'world' }, function (err, insertedDoc) {
        Object.keys(insertedDoc).length.should.equal(2)
        assert.isUndefined(insertedDoc.createdAt)
        assert.isUndefined(insertedDoc.updatedAt)

        // eslint-disable-next-line node/handle-callback-err
        d.find({}, function (err, docs) {
          docs.length.should.equal(1)
          assert.deepStrictEqual(docs[0], insertedDoc)

          done()
        })
      })
    })

    it('If timestampData is set but createdAt is specified by user, don\'t change it', function (done) {
      const newDoc = { hello: 'world', createdAt: new Date(234) }; const beginning = Date.now()
      d = new Datastore({ filename: testDb, timestampData: true, autoload: true })
      // eslint-disable-next-line node/handle-callback-err
      d.insert(newDoc, function (err, insertedDoc) {
        Object.keys(insertedDoc).length.should.equal(4)
        insertedDoc.createdAt.getTime().should.equal(234) // Not modified
        assert.isBelow(insertedDoc.updatedAt.getTime() - beginning, reloadTimeUpperBound) // Created

        // eslint-disable-next-line node/handle-callback-err
        d.find({}, function (err, docs) {
          assert.deepStrictEqual(insertedDoc, docs[0])

          d.loadDatabase(function () {
            // eslint-disable-next-line node/handle-callback-err
            d.find({}, function (err, docs) {
              assert.deepStrictEqual(insertedDoc, docs[0])

              done()
            })
          })
        })
      })
    })

    it('If timestampData is set but updatedAt is specified by user, don\'t change it', function (done) {
      const newDoc = { hello: 'world', updatedAt: new Date(234) }; const beginning = Date.now()
      d = new Datastore({ filename: testDb, timestampData: true, autoload: true })
      // eslint-disable-next-line node/handle-callback-err
      d.insert(newDoc, function (err, insertedDoc) {
        Object.keys(insertedDoc).length.should.equal(4)
        insertedDoc.updatedAt.getTime().should.equal(234) // Not modified
        assert.isBelow(insertedDoc.createdAt.getTime() - beginning, reloadTimeUpperBound) // Created

        // eslint-disable-next-line node/handle-callback-err
        d.find({}, function (err, docs) {
          assert.deepStrictEqual(insertedDoc, docs[0])

          d.loadDatabase(function () {
            // eslint-disable-next-line node/handle-callback-err
            d.find({}, function (err, docs) {
              assert.deepStrictEqual(insertedDoc, docs[0])

              done()
            })
          })
        })
      })
    })

    it('Can insert a doc with id 0', function (done) {
      // eslint-disable-next-line node/handle-callback-err
      d.insert({ _id: 0, hello: 'world' }, function (err, doc) {
        doc._id.should.equal(0)
        doc.hello.should.equal('world')
        done()
      })
    })

    /**
     * Complicated behavior here. Basically we need to test that when a user function throws an exception, it is not caught
     * in NeDB and the callback called again, transforming a user error into a NeDB error.
     *
     * So we need a way to check that the callback is called only once and the exception thrown is indeed the client exception
     * Mocha's exception handling mechanism interferes with this since it already registers a listener on uncaughtException
     * which we need to use since findOne is not called in the same turn of the event loop (so no try/catch)
     * So we remove all current listeners, put our own which when called will register the former listeners (incl. Mocha's) again.
     *
     * Note: maybe using an in-memory only NeDB would give us an easier solution
     */
    it('If the callback throws an uncaught exception, do not catch it inside findOne, this is userspace concern', function (done) {
      let tryCount = 0
      const currentUncaughtExceptionHandlers = process.listeners('uncaughtException')

      let i

      process.removeAllListeners('uncaughtException')

      process.on('uncaughtException', function MINE (ex) {
        process.removeAllListeners('uncaughtException')

        for (i = 0; i < currentUncaughtExceptionHandlers.length; i += 1) {
          process.on('uncaughtException', currentUncaughtExceptionHandlers[i])
        }

        ex.message.should.equal('SOME EXCEPTION')
        done()
      })

      d.insert({ a: 5 }, function () {
        // eslint-disable-next-line node/handle-callback-err
        d.findOne({ a: 5 }, function (err, doc) {
          if (tryCount === 0) {
            tryCount += 1
            throw new Error('SOME EXCEPTION')
          } else {
            done(new Error('Callback was called twice'))
          }
        })
      })
    })
  }) // ==== End of 'Insert' ==== //

  describe('#getCandidates', function () {
    it('Can use an index to get docs with a basic match', function (done) {
      // eslint-disable-next-line node/handle-callback-err
      d.ensureIndex({ fieldName: 'tf' }, function (err) {
        // eslint-disable-next-line node/handle-callback-err
        d.insert({ tf: 4 }, function (err, _doc1) {
          d.insert({ tf: 6 }, function () {
            // eslint-disable-next-line node/handle-callback-err
            d.insert({ tf: 4, an: 'other' }, function (err, _doc2) {
              d.insert({ tf: 9 }, function () {
                // eslint-disable-next-line node/handle-callback-err
                callbackify(query => d._getCandidatesAsync(query))({ r: 6, tf: 4 }, function (err, data) {
                  const doc1 = data.find(function (d) { return d._id === _doc1._id })
                  const doc2 = data.find(function (d) { return d._id === _doc2._id })

                  data.length.should.equal(2)
                  assert.deepStrictEqual(doc1, { _id: doc1._id, tf: 4 })
                  assert.deepStrictEqual(doc2, { _id: doc2._id, tf: 4, an: 'other' })

                  done()
                })
              })
            })
          })
        })
      })
    })

    it('Can use a compound index to get docs with a basic match', function (done) {
      // eslint-disable-next-line node/handle-callback-err
      d.ensureIndex({ fieldName: ['tf', 'tg'] }, function (err) {
        d.insert({ tf: 4, tg: 0, foo: 1 }, function () {
          d.insert({ tf: 6, tg: 0, foo: 2 }, function () {
            // eslint-disable-next-line node/handle-callback-err
            d.insert({ tf: 4, tg: 1, foo: 3 }, function (err, _doc1) {
              d.insert({ tf: 6, tg: 1, foo: 4 }, function () {
                // eslint-disable-next-line node/handle-callback-err
                callbackify(query => d._getCandidatesAsync(query))({ tf: 4, tg: 1 }, function (err, data) {
                  const doc1 = data.find(function (d) { return d._id === _doc1._id })

                  data.length.should.equal(1)
                  assert.deepEqual(doc1, { _id: doc1._id, tf: 4, tg: 1, foo: 3 })

                  done()
                })
              })
            })
          })
        })
      })
    })

    it('Can use an index to get docs with a $in match', function (done) {
      // eslint-disable-next-line node/handle-callback-err
      d.ensureIndex({ fieldName: 'tf' }, function (err) {
        // eslint-disable-next-line node/handle-callback-err
        d.insert({ tf: 4 }, function (err) {
          // eslint-disable-next-line node/handle-callback-err
          d.insert({ tf: 6 }, function (err, _doc1) {
            // eslint-disable-next-line node/handle-callback-err
            d.insert({ tf: 4, an: 'other' }, function (err) {
              // eslint-disable-next-line node/handle-callback-err
              d.insert({ tf: 9 }, function (err, _doc2) {
                // eslint-disable-next-line node/handle-callback-err
                callbackify(query => d._getCandidatesAsync(query))({ r: 6, tf: { $in: [6, 9, 5] } }, function (err, data) {
                  const doc1 = data.find(function (d) { return d._id === _doc1._id })
                  const doc2 = data.find(function (d) { return d._id === _doc2._id })

                  data.length.should.equal(2)
                  assert.deepStrictEqual(doc1, { _id: doc1._id, tf: 6 })
                  assert.deepStrictEqual(doc2, { _id: doc2._id, tf: 9 })

                  done()
                })
              })
            })
          })
        })
      })
    })

    it('If no index can be used, return the whole database', function (done) {
      // eslint-disable-next-line node/handle-callback-err
      d.ensureIndex({ fieldName: 'tf' }, function (err) {
        // eslint-disable-next-line node/handle-callback-err
        d.insert({ tf: 4 }, function (err, _doc1) {
          // eslint-disable-next-line node/handle-callback-err
          d.insert({ tf: 6 }, function (err, _doc2) {
            // eslint-disable-next-line node/handle-callback-err
            d.insert({ tf: 4, an: 'other' }, function (err, _doc3) {
              // eslint-disable-next-line node/handle-callback-err
              d.insert({ tf: 9 }, function (err, _doc4) {
                // eslint-disable-next-line node/handle-callback-err
                callbackify(query => d._getCandidatesAsync(query))({ r: 6, notf: { $in: [6, 9, 5] } }, function (err, data) {
                  const doc1 = data.find(function (d) { return d._id === _doc1._id })
                  const doc2 = data.find(function (d) { return d._id === _doc2._id })
                  const doc3 = data.find(function (d) { return d._id === _doc3._id })
                  const doc4 = data.find(function (d) { return d._id === _doc4._id })

                  data.length.should.equal(4)
                  assert.deepStrictEqual(doc1, { _id: doc1._id, tf: 4 })
                  assert.deepStrictEqual(doc2, { _id: doc2._id, tf: 6 })
                  assert.deepStrictEqual(doc3, { _id: doc3._id, tf: 4, an: 'other' })
                  assert.deepStrictEqual(doc4, { _id: doc4._id, tf: 9 })

                  done()
                })
              })
            })
          })
        })
      })
    })

    it('Can use indexes for comparison matches', function (done) {
      // eslint-disable-next-line node/handle-callback-err
      d.ensureIndex({ fieldName: 'tf' }, function (err) {
        // eslint-disable-next-line node/handle-callback-err
        d.insert({ tf: 4 }, function (err, _doc1) {
          // eslint-disable-next-line node/handle-callback-err
          d.insert({ tf: 6 }, function (err, _doc2) {
            // eslint-disable-next-line node/handle-callback-err
            d.insert({ tf: 4, an: 'other' }, function (err, _doc3) {
              // eslint-disable-next-line node/handle-callback-err
              d.insert({ tf: 9 }, function (err, _doc4) {
                // eslint-disable-next-line node/handle-callback-err
                callbackify(query => d._getCandidatesAsync(query))({ r: 6, tf: { $lte: 9, $gte: 6 } }, function (err, data) {
                  const doc2 = data.find(function (d) { return d._id === _doc2._id })
                  const doc4 = data.find(function (d) { return d._id === _doc4._id })

                  data.length.should.equal(2)
                  assert.deepStrictEqual(doc2, { _id: doc2._id, tf: 6 })
                  assert.deepStrictEqual(doc4, { _id: doc4._id, tf: 9 })

                  done()
                })
              })
            })
          })
        })
      })
    })

    it('Can set a TTL index that expires documents', function (done) {
      d.ensureIndex({ fieldName: 'exp', expireAfterSeconds: 0.2 }, function () {
        d.insert({ hello: 'world', exp: new Date() }, function () {
          setTimeout(function () {
            d.findOne({}, function (err, doc) {
              assert.isNull(err)
              doc.hello.should.equal('world')

              setTimeout(function () {
                d.findOne({}, function (err, doc) {
                  assert.isNull(err)
                  assert.isNull(doc)

                  d.on('compaction.done', function () {
                    // After compaction, no more mention of the document, correctly removed
                    const datafileContents = fs.readFileSync(testDb, 'utf8')
                    datafileContents.split('\n').length.should.equal(2)
                    assert.isNull(datafileContents.match(/world/))

                    // New datastore on same datafile is empty
                    const d2 = new Datastore({ filename: testDb, autoload: true })
                    d2.findOne({}, function (err, doc) {
                      assert.isNull(err)
                      assert.isNull(doc)

                      done()
                    })
                  })

                  d.compactDatafile()
                })
              }, 101)
            })
          }, 100)
        })
      })
    })

    it('TTL indexes can expire multiple documents and only what needs to be expired', function (done) {
      d.ensureIndex({ fieldName: 'exp', expireAfterSeconds: 0.2 }, function () {
        d.insert({ hello: 'world1', exp: new Date() }, function () {
          d.insert({ hello: 'world2', exp: new Date() }, function () {
            d.insert({ hello: 'world3', exp: new Date((new Date()).getTime() + 100) }, function () {
              setTimeout(function () {
                d.find({}, function (err, docs) {
                  assert.isNull(err)
                  docs.length.should.equal(3)

                  setTimeout(function () {
                    d.find({}, function (err, docs) {
                      assert.isNull(err)
                      docs.length.should.equal(1)
                      docs[0].hello.should.equal('world3')

                      setTimeout(function () {
                        d.find({}, function (err, docs) {
                          assert.isNull(err)
                          docs.length.should.equal(0)

                          done()
                        })
                      }, 101)
                    })
                  }, 101)
                })
              }, 100)
            })
          })
        })
      })
    })

    it('Document where indexed field is absent or not a date are ignored', function (done) {
      d.ensureIndex({ fieldName: 'exp', expireAfterSeconds: 0.2 }, function () {
        d.insert({ hello: 'world1', exp: new Date() }, function () {
          d.insert({ hello: 'world2', exp: 'not a date' }, function () {
            d.insert({ hello: 'world3' }, function () {
              setTimeout(function () {
                d.find({}, function (err, docs) {
                  assert.isNull(err)
                  docs.length.should.equal(3)

                  setTimeout(function () {
                    d.find({}, function (err, docs) {
                      assert.isNull(err)
                      docs.length.should.equal(2)

                      docs[0].hello.should.not.equal('world1')
                      docs[1].hello.should.not.equal('world1')

                      done()
                    })
                  }, 101)
                })
              }, 100)
            })
          })
        })
      })
    })
  }) // ==== End of '#getCandidates' ==== //

  describe('Find', function () {
    it('Can find all documents if an empty query is used', function (done) {
      waterfall([
        function (cb) {
          // eslint-disable-next-line node/handle-callback-err
          d.insert({ somedata: 'ok' }, function (err) {
            // eslint-disable-next-line node/handle-callback-err
            d.insert({ somedata: 'another', plus: 'additional data' }, function (err) {
              d.insert({ somedata: 'again' }, function (err) { return cb(err) })
            })
          })
        },
        function (cb) { // Test with empty object
          d.find({}, function (err, docs) {
            assert.isNull(err)
            docs.length.should.equal(3)
            docs.map(x => x.somedata).should.contain('ok')
            docs.map(x => x.somedata).should.contain('another')
            docs.find(function (d) { return d.somedata === 'another' }).plus.should.equal('additional data')
            docs.map(x => x.somedata).should.contain('again')
            return cb()
          })
        }
      ], done)
    })

    it('Can find all documents matching a basic query', function (done) {
      waterfall([
        function (cb) {
          // eslint-disable-next-line node/handle-callback-err
          d.insert({ somedata: 'ok' }, function (err) {
            // eslint-disable-next-line node/handle-callback-err
            d.insert({ somedata: 'again', plus: 'additional data' }, function (err) {
              d.insert({ somedata: 'again' }, function (err) { return cb(err) })
            })
          })
        },
        function (cb) { // Test with query that will return docs
          d.find({ somedata: 'again' }, function (err, docs) {
            assert.isNull(err)
            docs.length.should.equal(2)
            docs.map(x => x.somedata).should.not.contain('ok')
            return cb()
          })
        },
        function (cb) { // Test with query that doesn't match anything
          d.find({ somedata: 'nope' }, function (err, docs) {
            assert.isNull(err)
            docs.length.should.equal(0)
            return cb()
          })
        }
      ], done)
    })

    it('Can find one document matching a basic query and return null if none is found', function (done) {
      waterfall([
        function (cb) {
          // eslint-disable-next-line node/handle-callback-err
          d.insert({ somedata: 'ok' }, function (err) {
            // eslint-disable-next-line node/handle-callback-err
            d.insert({ somedata: 'again', plus: 'additional data' }, function (err) {
              d.insert({ somedata: 'again' }, function (err) { return cb(err) })
            })
          })
        },
        function (cb) { // Test with query that will return docs
          d.findOne({ somedata: 'ok' }, function (err, doc) {
            assert.isNull(err)
            Object.keys(doc).length.should.equal(2)
            doc.somedata.should.equal('ok')
            assert.isDefined(doc._id)
            return cb()
          })
        },
        function (cb) { // Test with query that doesn't match anything
          d.findOne({ somedata: 'nope' }, function (err, doc) {
            assert.isNull(err)
            assert.isNull(doc)
            return cb()
          })
        }
      ], done)
    })

    it('Can find dates and objects (non JS-native types)', function (done) {
      const date1 = new Date(1234543)
      const date2 = new Date(9999)

      d.insert({ now: date1, sth: { name: 'nedb' } }, function () {
        d.findOne({ now: date1 }, function (err, doc) {
          assert.isNull(err)
          doc.sth.name.should.equal('nedb')

          d.findOne({ now: date2 }, function (err, doc) {
            assert.isNull(err)
            assert.isNull(doc)

            d.findOne({ sth: { name: 'nedb' } }, function (err, doc) {
              assert.isNull(err)
              doc.sth.name.should.equal('nedb')

              d.findOne({ sth: { name: 'other' } }, function (err, doc) {
                assert.isNull(err)
                assert.isNull(doc)

                done()
              })
            })
          })
        })
      })
    })

    it('Can use dot-notation to query subfields', function (done) {
      d.insert({ greeting: { english: 'hello' } }, function () {
        d.findOne({ 'greeting.english': 'hello' }, function (err, doc) {
          assert.isNull(err)
          doc.greeting.english.should.equal('hello')

          d.findOne({ 'greeting.english': 'hellooo' }, function (err, doc) {
            assert.isNull(err)
            assert.isNull(doc)

            d.findOne({ 'greeting.englis': 'hello' }, function (err, doc) {
              assert.isNull(err)
              assert.isNull(doc)

              done()
            })
          })
        })
      })
    })

    it('Array fields match if any element matches', function (done) {
      // eslint-disable-next-line node/handle-callback-err
      d.insert({ fruits: ['pear', 'apple', 'banana'] }, function (err, doc1) {
        // eslint-disable-next-line node/handle-callback-err
        d.insert({ fruits: ['coconut', 'orange', 'pear'] }, function (err, doc2) {
          // eslint-disable-next-line node/handle-callback-err
          d.insert({ fruits: ['banana'] }, function (err, doc3) {
            d.find({ fruits: 'pear' }, function (err, docs) {
              assert.isNull(err)
              docs.length.should.equal(2)
              docs.map(x => x._id).should.contain(doc1._id)
              docs.map(x => x._id).should.contain(doc2._id)

              d.find({ fruits: 'banana' }, function (err, docs) {
                assert.isNull(err)
                docs.length.should.equal(2)
                docs.map(x => x._id).should.contain(doc1._id)
                docs.map(x => x._id).should.contain(doc3._id)

                d.find({ fruits: 'doesntexist' }, function (err, docs) {
                  assert.isNull(err)
                  docs.length.should.equal(0)

                  done()
                })
              })
            })
          })
        })
      })
    })

    it('Returns an error if the query is not well formed', function (done) {
      d.insert({ hello: 'world' }, function () {
        d.find({ $or: { hello: 'world' } }, function (err, docs) {
          assert.isDefined(err)
          assert.isUndefined(docs)

          d.findOne({ $or: { hello: 'world' } }, function (err, doc) {
            assert.isDefined(err)
            assert.isUndefined(doc)

            done()
          })
        })
      })
    })

    it('Changing the documents returned by find or findOne do not change the database state', function (done) {
      d.insert({ a: 2, hello: 'world' }, function () {
        // eslint-disable-next-line node/handle-callback-err
        d.findOne({ a: 2 }, function (err, doc) {
          doc.hello = 'changed'

          // eslint-disable-next-line node/handle-callback-err
          d.findOne({ a: 2 }, function (err, doc) {
            doc.hello.should.equal('world')

            // eslint-disable-next-line node/handle-callback-err
            d.find({ a: 2 }, function (err, docs) {
              docs[0].hello = 'changed'

              // eslint-disable-next-line node/handle-callback-err
              d.findOne({ a: 2 }, function (err, doc) {
                doc.hello.should.equal('world')

                done()
              })
            })
          })
        })
      })
    })

    it('Can use sort, skip and limit if the callback is not passed to find but to exec', function (done) {
      d.insert({ a: 2, hello: 'world' }, function () {
        d.insert({ a: 24, hello: 'earth' }, function () {
          d.insert({ a: 13, hello: 'blueplanet' }, function () {
            d.insert({ a: 15, hello: 'home' }, function () {
              d.find({}).sort({ a: 1 }).limit(2).exec(function (err, docs) {
                assert.isNull(err)
                docs.length.should.equal(2)
                docs[0].hello.should.equal('world')
                docs[1].hello.should.equal('blueplanet')
                done()
              })
            })
          })
        })
      })
    })

    it('Can use sort and skip if the callback is not passed to findOne but to exec', function (done) {
      d.insert({ a: 2, hello: 'world' }, function () {
        d.insert({ a: 24, hello: 'earth' }, function () {
          d.insert({ a: 13, hello: 'blueplanet' }, function () {
            d.insert({ a: 15, hello: 'home' }, function () {
              // No skip no query
              d.findOne({}).sort({ a: 1 }).exec(function (err, doc) {
                assert.isNull(err)
                doc.hello.should.equal('world')

                // A query
                d.findOne({ a: { $gt: 14 } }).sort({ a: 1 }).exec(function (err, doc) {
                  assert.isNull(err)
                  doc.hello.should.equal('home')

                  // And a skip
                  d.findOne({ a: { $gt: 14 } }).sort({ a: 1 }).skip(1).exec(function (err, doc) {
                    assert.isNull(err)
                    doc.hello.should.equal('earth')

                    // No result
                    d.findOne({ a: { $gt: 14 } }).sort({ a: 1 }).skip(2).exec(function (err, doc) {
                      assert.isNull(err)
                      assert.isNull(doc)

                      done()
                    })
                  })
                })
              })
            })
          })
        })
      })
    })

    it('Can use projections in find, normal or cursor way', function (done) {
      // eslint-disable-next-line node/handle-callback-err
      d.insert({ a: 2, hello: 'world' }, function (err, doc0) {
        // eslint-disable-next-line node/handle-callback-err
        d.insert({ a: 24, hello: 'earth' }, function (err, doc1) {
          d.find({ a: 2 }, { a: 0, _id: 0 }, function (err, docs) {
            assert.isNull(err)
            docs.length.should.equal(1)
            assert.deepStrictEqual(docs[0], { hello: 'world' })

            d.find({ a: 2 }, { a: 0, _id: 0 }).exec(function (err, docs) {
              assert.isNull(err)
              docs.length.should.equal(1)
              assert.deepStrictEqual(docs[0], { hello: 'world' })

              // Can't use both modes at once if not _id
              d.find({ a: 2 }, { a: 0, hello: 1 }, function (err, docs) {
                assert.isNotNull(err)
                assert.isUndefined(docs)

                d.find({ a: 2 }, { a: 0, hello: 1 }).exec(function (err, docs) {
                  assert.isNotNull(err)
                  assert.isUndefined(docs)

                  done()
                })
              })
            })
          })
        })
      })
    })

    it('Can use projections in findOne, normal or cursor way', function (done) {
      // eslint-disable-next-line node/handle-callback-err
      d.insert({ a: 2, hello: 'world' }, function (err, doc0) {
        // eslint-disable-next-line node/handle-callback-err
        d.insert({ a: 24, hello: 'earth' }, function (err, doc1) {
          d.findOne({ a: 2 }, { a: 0, _id: 0 }, function (err, doc) {
            assert.isNull(err)
            assert.deepStrictEqual(doc, { hello: 'world' })

            d.findOne({ a: 2 }, { a: 0, _id: 0 }).exec(function (err, doc) {
              assert.isNull(err)
              assert.deepStrictEqual(doc, { hello: 'world' })

              // Can't use both modes at once if not _id
              d.findOne({ a: 2 }, { a: 0, hello: 1 }, function (err, doc) {
                assert.isNotNull(err)
                assert.isUndefined(doc)

                d.findOne({ a: 2 }, { a: 0, hello: 1 }).exec(function (err, doc) {
                  assert.isNotNull(err)
                  assert.isUndefined(doc)

                  done()
                })
              })
            })
          })
        })
      })
    })
  }) // ==== End of 'Find' ==== //

  describe('Count', function () {
    it('Count all documents if an empty query is used', function (done) {
      waterfall([
        function (cb) {
          // eslint-disable-next-line node/handle-callback-err
          d.insert({ somedata: 'ok' }, function (err) {
            // eslint-disable-next-line node/handle-callback-err
            d.insert({ somedata: 'another', plus: 'additional data' }, function (err) {
              d.insert({ somedata: 'again' }, function (err) { return cb(err) })
            })
          })
        },
        function (cb) { // Test with empty object
          d.count({}, function (err, docs) {
            assert.isNull(err)
            docs.should.equal(3)
            return cb()
          })
        }
      ], done)
    })

    it('Count all documents matching a basic query', function (done) {
      waterfall([
        function (cb) {
          // eslint-disable-next-line node/handle-callback-err
          d.insert({ somedata: 'ok' }, function (err) {
            // eslint-disable-next-line node/handle-callback-err
            d.insert({ somedata: 'again', plus: 'additional data' }, function (err) {
              d.insert({ somedata: 'again' }, function (err) { return cb(err) })
            })
          })
        },
        function (cb) { // Test with query that will return docs
          d.count({ somedata: 'again' }, function (err, docs) {
            assert.isNull(err)
            docs.should.equal(2)
            return cb()
          })
        },
        function (cb) { // Test with query that doesn't match anything
          d.count({ somedata: 'nope' }, function (err, docs) {
            assert.isNull(err)
            docs.should.equal(0)
            return cb()
          })
        }
      ], done)
    })

    it('Array fields match if any element matches', function (done) {
      // eslint-disable-next-line node/handle-callback-err
      d.insert({ fruits: ['pear', 'apple', 'banana'] }, function (err, doc1) {
        // eslint-disable-next-line node/handle-callback-err
        d.insert({ fruits: ['coconut', 'orange', 'pear'] }, function (err, doc2) {
          // eslint-disable-next-line node/handle-callback-err
          d.insert({ fruits: ['banana'] }, function (err, doc3) {
            d.count({ fruits: 'pear' }, function (err, docs) {
              assert.isNull(err)
              docs.should.equal(2)

              d.count({ fruits: 'banana' }, function (err, docs) {
                assert.isNull(err)
                docs.should.equal(2)

                d.count({ fruits: 'doesntexist' }, function (err, docs) {
                  assert.isNull(err)
                  docs.should.equal(0)

                  done()
                })
              })
            })
          })
        })
      })
    })

    it('Returns an error if the query is not well formed', function (done) {
      d.insert({ hello: 'world' }, function () {
        d.count({ $or: { hello: 'world' } }, function (err, docs) {
          assert.isDefined(err)
          assert.isUndefined(docs)

          done()
        })
      })
    })
  })

  describe('Update', function () {
    it('If the query doesn\'t match anything, database is not modified', function (done) {
      waterfall([
        function (cb) {
          // eslint-disable-next-line node/handle-callback-err
          d.insert({ somedata: 'ok' }, function (err) {
            // eslint-disable-next-line node/handle-callback-err
            d.insert({ somedata: 'again', plus: 'additional data' }, function (err) {
              d.insert({ somedata: 'another' }, function (err) { return cb(err) })
            })
          })
        },
        function (cb) { // Test with query that doesn't match anything
          d.update({ somedata: 'nope' }, { newDoc: 'yes' }, { multi: true }, function (err, n) {
            assert.isNull(err)
            n.should.equal(0)

            // eslint-disable-next-line node/handle-callback-err
            d.find({}, function (err, docs) {
              const doc1 = docs.find(function (d) { return d.somedata === 'ok' })
              const doc2 = docs.find(function (d) { return d.somedata === 'again' })
              const doc3 = docs.find(function (d) { return d.somedata === 'another' })

              docs.length.should.equal(3)
              assert.isUndefined(docs.find(function (d) { return d.newDoc === 'yes' }))

              assert.deepStrictEqual(doc1, { _id: doc1._id, somedata: 'ok' })
              assert.deepStrictEqual(doc2, { _id: doc2._id, somedata: 'again', plus: 'additional data' })
              assert.deepStrictEqual(doc3, { _id: doc3._id, somedata: 'another' })

              return cb()
            })
          })
        }
      ], done)
    })

    it('If timestampData option is set, update the updatedAt field', function (done) {
      const beginning = Date.now()
      d = new Datastore({ filename: testDb, autoload: true, timestampData: true })
      // eslint-disable-next-line node/handle-callback-err
      d.insert({ hello: 'world' }, function (err, insertedDoc) {
        assert.isBelow(insertedDoc.updatedAt.getTime() - beginning, reloadTimeUpperBound)
        assert.isBelow(insertedDoc.createdAt.getTime() - beginning, reloadTimeUpperBound)
        Object.keys(insertedDoc).length.should.equal(4)

        // Wait 100ms before performing the update
        setTimeout(function () {
          const step1 = Date.now()
          d.update({ _id: insertedDoc._id }, { $set: { hello: 'mars' } }, {}, function () {
            // eslint-disable-next-line node/handle-callback-err
            d.find({ _id: insertedDoc._id }, function (err, docs) {
              docs.length.should.equal(1)
              Object.keys(docs[0]).length.should.equal(4)
              docs[0]._id.should.equal(insertedDoc._id)
              docs[0].createdAt.should.equal(insertedDoc.createdAt)
              docs[0].hello.should.equal('mars')
              assert.isAbove(docs[0].updatedAt.getTime() - beginning, 99) // updatedAt modified
              assert.isBelow(docs[0].updatedAt.getTime() - step1, reloadTimeUpperBound) // updatedAt modified

              done()
            })
          })
        }, 100)
      })
    })

    it('Can update multiple documents matching the query', function (done) {
      let id1
      let id2
      let id3

      // Test DB state after update and reload
      function testPostUpdateState (cb) {
        // eslint-disable-next-line node/handle-callback-err
        d.find({}, function (err, docs) {
          const doc1 = docs.find(function (d) { return d._id === id1 })
          const doc2 = docs.find(function (d) { return d._id === id2 })
          const doc3 = docs.find(function (d) { return d._id === id3 })

          docs.length.should.equal(3)

          Object.keys(doc1).length.should.equal(2)
          doc1.somedata.should.equal('ok')
          doc1._id.should.equal(id1)

          Object.keys(doc2).length.should.equal(2)
          doc2.newDoc.should.equal('yes')
          doc2._id.should.equal(id2)

          Object.keys(doc3).length.should.equal(2)
          doc3.newDoc.should.equal('yes')
          doc3._id.should.equal(id3)

          return cb()
        })
      }

      // Actually launch the tests
      waterfall([
        function (cb) {
          // eslint-disable-next-line node/handle-callback-err
          d.insert({ somedata: 'ok' }, function (err, doc1) {
            id1 = doc1._id
            // eslint-disable-next-line node/handle-callback-err
            d.insert({ somedata: 'again', plus: 'additional data' }, function (err, doc2) {
              id2 = doc2._id
              d.insert({ somedata: 'again' }, function (err, doc3) {
                id3 = doc3._id
                return cb(err)
              })
            })
          })
        },
        function (cb) {
          d.update({ somedata: 'again' }, { newDoc: 'yes' }, { multi: true }, function (err, n) {
            assert.isNull(err)
            n.should.equal(2)
            return cb()
          })
        },
        apply(testPostUpdateState),
        function (cb) {
          d.loadDatabase(function (err) { cb(err) })
        },
        apply(testPostUpdateState)
      ], done)
    })

    it('Can update only one document matching the query', function (done) {
      let id1
      let id2
      let id3

      // Test DB state after update and reload
      function testPostUpdateState (cb) {
        // eslint-disable-next-line node/handle-callback-err
        d.find({}, function (err, docs) {
          const doc1 = docs.find(function (d) { return d._id === id1 })
          const doc2 = docs.find(function (d) { return d._id === id2 })
          const doc3 = docs.find(function (d) { return d._id === id3 })

          docs.length.should.equal(3)

          assert.deepStrictEqual(doc1, { somedata: 'ok', _id: doc1._id })

          // doc2 or doc3 was modified. Since we sort on _id and it is random
          // it can be either of two situations
          try {
            assert.deepStrictEqual(doc2, { newDoc: 'yes', _id: doc2._id })
            assert.deepStrictEqual(doc3, { somedata: 'again', _id: doc3._id })
          } catch (e) {
            assert.deepStrictEqual(doc2, { somedata: 'again', plus: 'additional data', _id: doc2._id })
            assert.deepStrictEqual(doc3, { newDoc: 'yes', _id: doc3._id })
          }

          return cb()
        })
      }

      // Actually launch the test
      waterfall([
        function (cb) {
          // eslint-disable-next-line node/handle-callback-err
          d.insert({ somedata: 'ok' }, function (err, doc1) {
            id1 = doc1._id
            // eslint-disable-next-line node/handle-callback-err
            d.insert({ somedata: 'again', plus: 'additional data' }, function (err, doc2) {
              id2 = doc2._id
              d.insert({ somedata: 'again' }, function (err, doc3) {
                id3 = doc3._id
                return cb(err)
              })
            })
          })
        },
        function (cb) { // Test with query that doesn't match anything
          d.update({ somedata: 'again' }, { newDoc: 'yes' }, { multi: false }, function (err, n) {
            assert.isNull(err)
            n.should.equal(1)
            return cb()
          })
        },
        apply(testPostUpdateState),
        function (cb) {
          d.loadDatabase(function (err) { return cb(err) })
        },
        apply(testPostUpdateState) // The persisted state has been updated
      ], done)
    })

    describe('Upserts', function () {
      it('Can perform upserts if needed', function (done) {
        d.update({ impossible: 'db is empty anyway' }, { newDoc: true }, {}, function (err, nr, affectedDocuments) {
          assert.isNull(err)
          nr.should.equal(0)
          assert.isNull(affectedDocuments)

          // eslint-disable-next-line node/handle-callback-err
          d.find({}, function (err, docs) {
            docs.length.should.equal(0) // Default option for upsert is false

            d.update({ impossible: 'db is empty anyway' }, { something: 'created ok' }, { upsert: true }, function (err, nr, newDoc) {
              assert.isNull(err)
              nr.should.equal(1)
              newDoc.something.should.equal('created ok')
              assert.isDefined(newDoc._id)

              // eslint-disable-next-line node/handle-callback-err
              d.find({}, function (err, docs) {
                docs.length.should.equal(1) // Default option for upsert is false
                docs[0].something.should.equal('created ok')

                // Modifying the returned upserted document doesn't modify the database
                newDoc.newField = true
                // eslint-disable-next-line node/handle-callback-err
                d.find({}, function (err, docs) {
                  docs[0].something.should.equal('created ok')
                  assert.isUndefined(docs[0].newField)

                  done()
                })
              })
            })
          })
        })
      })

      it('If the update query is a normal object with no modifiers, it is the doc that will be upserted', function (done) {
        // eslint-disable-next-line node/handle-callback-err
        d.update({ $or: [{ a: 4 }, { a: 5 }] }, { hello: 'world', bloup: 'blap' }, { upsert: true }, function (err) {
          d.find({}, function (err, docs) {
            assert.isNull(err)
            docs.length.should.equal(1)
            const doc = docs[0]
            Object.keys(doc).length.should.equal(3)
            doc.hello.should.equal('world')
            doc.bloup.should.equal('blap')
            done()
          })
        })
      })

      it('If the update query contains modifiers, it is applied to the object resulting from removing all operators from the find query 1', function (done) {
        d.update({ $or: [{ a: 4 }, { a: 5 }] }, {
          $set: { hello: 'world' },
          $inc: { bloup: 3 }
          // eslint-disable-next-line node/handle-callback-err
        }, { upsert: true }, function (err) {
          d.find({ hello: 'world' }, function (err, docs) {
            assert.isNull(err)
            docs.length.should.equal(1)
            const doc = docs[0]
            Object.keys(doc).length.should.equal(3)
            doc.hello.should.equal('world')
            doc.bloup.should.equal(3)
            done()
          })
        })
      })

      it('If the update query contains modifiers, it is applied to the object resulting from removing all operators from the find query 2', function (done) {
        d.update({ $or: [{ a: 4 }, { a: 5 }], cac: 'rrr' }, {
          $set: { hello: 'world' },
          $inc: { bloup: 3 }
          // eslint-disable-next-line node/handle-callback-err
        }, { upsert: true }, function (err) {
          d.find({ hello: 'world' }, function (err, docs) {
            assert.isNull(err)
            docs.length.should.equal(1)
            const doc = docs[0]
            Object.keys(doc).length.should.equal(4)
            doc.cac.should.equal('rrr')
            doc.hello.should.equal('world')
            doc.bloup.should.equal(3)
            done()
          })
        })
      })

      it('Performing upsert with badly formatted fields yields a standard error not an exception', function (done) {
        d.update({ _id: '1234' }, { $set: { $$badfield: 5 } }, { upsert: true }, function (err, doc) {
          assert.isDefined(err)
          done()
        })
      })
    }) // ==== End of 'Upserts' ==== //

    it('Cannot perform update if the update query is not either registered-modifiers-only or copy-only, or contain badly formatted fields', function (done) {
      d.insert({ something: 'yup' }, function () {
        d.update({}, { boom: { $badfield: 5 } }, { multi: false }, function (err) {
          assert.isDefined(err)

          d.update({}, { boom: { 'bad.field': 5 } }, { multi: false }, function (err) {
            assert.isDefined(err)

            d.update({}, { $inc: { test: 5 }, mixed: 'rrr' }, { multi: false }, function (err) {
              assert.isDefined(err)

              d.update({}, { $inexistent: { test: 5 } }, { multi: false }, function (err) {
                assert.isDefined(err)

                done()
              })
            })
          })
        })
      })
    })

    it('Can update documents using multiple modifiers', function (done) {
      let id

      // eslint-disable-next-line node/handle-callback-err
      d.insert({ something: 'yup', other: 40 }, function (err, newDoc) {
        id = newDoc._id

        d.update({}, { $set: { something: 'changed' }, $inc: { other: 10 } }, { multi: false }, function (err, nr) {
          assert.isNull(err)
          nr.should.equal(1)

          // eslint-disable-next-line node/handle-callback-err
          d.findOne({ _id: id }, function (err, doc) {
            Object.keys(doc).length.should.equal(3)
            doc._id.should.equal(id)
            doc.something.should.equal('changed')
            doc.other.should.equal(50)

            done()
          })
        })
      })
    })

    it('Can upsert a document even with modifiers', function (done) {
      d.update({ bloup: 'blap' }, { $set: { hello: 'world' } }, { upsert: true }, function (err, nr, newDoc) {
        assert.isNull(err)
        nr.should.equal(1)
        newDoc.bloup.should.equal('blap')
        newDoc.hello.should.equal('world')
        assert.isDefined(newDoc._id)

        // eslint-disable-next-line node/handle-callback-err
        d.find({}, function (err, docs) {
          docs.length.should.equal(1)
          Object.keys(docs[0]).length.should.equal(3)
          docs[0].hello.should.equal('world')
          docs[0].bloup.should.equal('blap')
          assert.isDefined(docs[0]._id)

          done()
        })
      })
    })

    it('When using modifiers, the only way to update subdocs is with the dot-notation', function (done) {
      d.insert({ bloup: { blip: 'blap', other: true } }, function () {
        // Correct methos
        d.update({}, { $set: { 'bloup.blip': 'hello' } }, {}, function () {
          // eslint-disable-next-line node/handle-callback-err
          d.findOne({}, function (err, doc) {
            doc.bloup.blip.should.equal('hello')
            doc.bloup.other.should.equal(true)

            // Wrong
            d.update({}, { $set: { bloup: { blip: 'ola' } } }, {}, function () {
              // eslint-disable-next-line node/handle-callback-err
              d.findOne({}, function (err, doc) {
                doc.bloup.blip.should.equal('ola')
                assert.isUndefined(doc.bloup.other) // This information was lost

                done()
              })
            })
          })
        })
      })
    })

    it('Returns an error if the query is not well formed', function (done) {
      d.insert({ hello: 'world' }, function () {
        d.update({ $or: { hello: 'world' } }, { a: 1 }, {}, function (err, nr, upsert) {
          assert.isDefined(err)
          assert.isUndefined(nr)
          assert.isUndefined(upsert)

          done()
        })
      })
    })

    it('If an error is thrown by a modifier, the database state is not changed', function (done) {
      // eslint-disable-next-line node/handle-callback-err
      d.insert({ hello: 'world' }, function (err, newDoc) {
        d.update({}, { $inc: { hello: 4 } }, {}, function (err, nr) {
          assert.isDefined(err)
          assert.isUndefined(nr)

          // eslint-disable-next-line node/handle-callback-err
          d.find({}, function (err, docs) {
            assert.deepStrictEqual(docs, [{ _id: newDoc._id, hello: 'world' }])

            done()
          })
        })
      })
    })

    it('Cant change the _id of a document', function (done) {
      // eslint-disable-next-line node/handle-callback-err
      d.insert({ a: 2 }, function (err, newDoc) {
        d.update({ a: 2 }, { a: 2, _id: 'nope' }, {}, function (err) {
          assert.isDefined(err)

          // eslint-disable-next-line node/handle-callback-err
          d.find({}, function (err, docs) {
            docs.length.should.equal(1)
            Object.keys(docs[0]).length.should.equal(2)
            docs[0].a.should.equal(2)
            docs[0]._id.should.equal(newDoc._id)

            d.update({ a: 2 }, { $set: { _id: 'nope' } }, {}, function (err) {
              assert.isDefined(err)

              // eslint-disable-next-line node/handle-callback-err
              d.find({}, function (err, docs) {
                docs.length.should.equal(1)
                Object.keys(docs[0]).length.should.equal(2)
                docs[0].a.should.equal(2)
                docs[0]._id.should.equal(newDoc._id)

                done()
              })
            })
          })
        })
      })
    })

    it('Non-multi updates are persistent', function (done) {
      // eslint-disable-next-line node/handle-callback-err
      d.insert({ a: 1, hello: 'world' }, function (err, doc1) {
        // eslint-disable-next-line node/handle-callback-err
        d.insert({ a: 2, hello: 'earth' }, function (err, doc2) {
          d.update({ a: 2 }, { $set: { hello: 'changed' } }, {}, function (err) {
            assert.isNull(err)

            // eslint-disable-next-line node/handle-callback-err
            d.find({}, function (err, docs) {
              docs.sort(function (a, b) { return a.a - b.a })
              docs.length.should.equal(2)
              assert.deepStrictEqual(docs[0], { _id: doc1._id, a: 1, hello: 'world' })
              assert.deepStrictEqual(docs[1], { _id: doc2._id, a: 2, hello: 'changed' })

              // Even after a reload the database state hasn't changed
              d.loadDatabase(function (err) {
                assert.isNull(err)

                // eslint-disable-next-line node/handle-callback-err
                d.find({}, function (err, docs) {
                  docs.sort(function (a, b) { return a.a - b.a })
                  docs.length.should.equal(2)
                  assert.deepStrictEqual(docs[0], { _id: doc1._id, a: 1, hello: 'world' })
                  assert.deepStrictEqual(docs[1], { _id: doc2._id, a: 2, hello: 'changed' })

                  done()
                })
              })
            })
          })
        })
      })
    })

    it('Multi updates are persistent', function (done) {
      // eslint-disable-next-line node/handle-callback-err
      d.insert({ a: 1, hello: 'world' }, function (err, doc1) {
        // eslint-disable-next-line node/handle-callback-err
        d.insert({ a: 2, hello: 'earth' }, function (err, doc2) {
          // eslint-disable-next-line node/handle-callback-err
          d.insert({ a: 5, hello: 'pluton' }, function (err, doc3) {
            d.update({ a: { $in: [1, 2] } }, { $set: { hello: 'changed' } }, { multi: true }, function (err) {
              assert.isNull(err)

              // eslint-disable-next-line node/handle-callback-err
              d.find({}, function (err, docs) {
                docs.sort(function (a, b) { return a.a - b.a })
                docs.length.should.equal(3)
                assert.deepStrictEqual(docs[0], { _id: doc1._id, a: 1, hello: 'changed' })
                assert.deepStrictEqual(docs[1], { _id: doc2._id, a: 2, hello: 'changed' })
                assert.deepStrictEqual(docs[2], { _id: doc3._id, a: 5, hello: 'pluton' })

                // Even after a reload the database state hasn't changed
                d.loadDatabase(function (err) {
                  assert.isNull(err)

                  // eslint-disable-next-line node/handle-callback-err
                  d.find({}, function (err, docs) {
                    docs.sort(function (a, b) { return a.a - b.a })
                    docs.length.should.equal(3)
                    assert.deepStrictEqual(docs[0], { _id: doc1._id, a: 1, hello: 'changed' })
                    assert.deepStrictEqual(docs[1], { _id: doc2._id, a: 2, hello: 'changed' })
                    assert.deepStrictEqual(docs[2], { _id: doc3._id, a: 5, hello: 'pluton' })

                    done()
                  })
                })
              })
            })
          })
        })
      })
    })

    it('Can update without the options arg (will use defaults then)', function (done) {
      // eslint-disable-next-line node/handle-callback-err
      d.insert({ a: 1, hello: 'world' }, function (err, doc1) {
        // eslint-disable-next-line node/handle-callback-err
        d.insert({ a: 2, hello: 'earth' }, function (err, doc2) {
          // eslint-disable-next-line node/handle-callback-err
          d.insert({ a: 5, hello: 'pluton' }, function (err, doc3) {
            d.update({ a: 2 }, { $inc: { a: 10 } }, function (err, nr) {
              assert.isNull(err)
              nr.should.equal(1)
              // eslint-disable-next-line node/handle-callback-err
              d.find({}, function (err, docs) {
                const d1 = docs.find(function (doc) { return doc._id === doc1._id })
                const d2 = docs.find(function (doc) { return doc._id === doc2._id })
                const d3 = docs.find(function (doc) { return doc._id === doc3._id })

                d1.a.should.equal(1)
                d2.a.should.equal(12)
                d3.a.should.equal(5)

                done()
              })
            })
          })
        })
      })
    })

    it('If a multi update fails on one document, previous updates should be rolled back', function (done) {
      d.ensureIndex({ fieldName: 'a' })
      // eslint-disable-next-line node/handle-callback-err
      d.insert({ a: 4 }, function (err, doc1) {
        // eslint-disable-next-line node/handle-callback-err
        d.insert({ a: 5 }, function (err, doc2) {
          // eslint-disable-next-line node/handle-callback-err
          d.insert({ a: 'abc' }, function (err, doc3) {
            // With this query, candidates are always returned in the order 4, 5, 'abc' so it's always the last one which fails
            d.update({ a: { $in: [4, 5, 'abc'] } }, { $inc: { a: 10 } }, { multi: true }, function (err) {
              assert.isDefined(err)

              // No index modified
              for (const key in d.indexes) {
                if (Object.prototype.hasOwnProperty.call(d.indexes, key)) {
                  const index = d.indexes[key]
                  const docs = index.getAll()
                  const d1 = docs.find(function (doc) { return doc._id === doc1._id })
                  const d2 = docs.find(function (doc) { return doc._id === doc2._id })
                  const d3 = docs.find(function (doc) { return doc._id === doc3._id })

                  // All changes rolled back, including those that didn't trigger an error
                  d1.a.should.equal(4)
                  d2.a.should.equal(5)
                  d3.a.should.equal('abc')
                }
              }
              done()
            })
          })
        })
      })
    })

    it('If an index constraint is violated by an update, all changes should be rolled back', function (done) {
      d.ensureIndex({ fieldName: 'a', unique: true })
      // eslint-disable-next-line node/handle-callback-err
      d.insert({ a: 4 }, function (err, doc1) {
        // eslint-disable-next-line node/handle-callback-err
        d.insert({ a: 5 }, function (err, doc2) {
          // With this query, candidates are always returned in the order 4, 5, 'abc' so it's always the last one which fails
          d.update({ a: { $in: [4, 5, 'abc'] } }, { $set: { a: 10 } }, { multi: true }, function (err) {
            assert.isDefined(err)

            // Check that no index was modified
            for (const key in d.indexes) {
              if (Object.prototype.hasOwnProperty.call(d.indexes, key)) {
                const index = d.indexes[key]
                const docs = index.getAll()
                const d1 = docs.find(function (doc) { return doc._id === doc1._id })
                const d2 = docs.find(function (doc) { return doc._id === doc2._id })

                d1.a.should.equal(4)
                d2.a.should.equal(5)
              }
            }
            done()
          })
        })
      })
    })

    it('If options.returnUpdatedDocs is true, return all matched docs', function (done) {
      // eslint-disable-next-line node/handle-callback-err
      d.insert([{ a: 4 }, { a: 5 }, { a: 6 }], function (err, docs) {
        docs.length.should.equal(3)

        d.update({ a: 7 }, { $set: { u: 1 } }, {
          multi: true,
          returnUpdatedDocs: true
          // eslint-disable-next-line node/handle-callback-err
        }, function (err, num, updatedDocs) {
          num.should.equal(0)
          updatedDocs.length.should.equal(0)

          d.update({ a: 5 }, { $set: { u: 2 } }, {
            multi: true,
            returnUpdatedDocs: true
            // eslint-disable-next-line node/handle-callback-err
          }, function (err, num, updatedDocs) {
            num.should.equal(1)
            updatedDocs.length.should.equal(1)
            updatedDocs[0].a.should.equal(5)
            updatedDocs[0].u.should.equal(2)

            d.update({ a: { $in: [4, 6] } }, { $set: { u: 3 } }, {
              multi: true,
              returnUpdatedDocs: true
              // eslint-disable-next-line node/handle-callback-err
            }, function (err, num, updatedDocs) {
              num.should.equal(2)
              updatedDocs.length.should.equal(2)
              updatedDocs[0].u.should.equal(3)
              updatedDocs[1].u.should.equal(3)
              if (updatedDocs[0].a === 4) {
                updatedDocs[0].a.should.equal(4)
                updatedDocs[1].a.should.equal(6)
              } else {
                updatedDocs[0].a.should.equal(6)
                updatedDocs[1].a.should.equal(4)
              }

              done()
            })
          })
        })
      })
    })

    it('createdAt property is unchanged and updatedAt correct after an update, even a complete document replacement', function (done) {
      const d2 = new Datastore({ inMemoryOnly: true, timestampData: true })
      d2.insert({ a: 1 })
      // eslint-disable-next-line node/handle-callback-err
      d2.findOne({ a: 1 }, function (err, doc) {
        const createdAt = doc.createdAt.getTime()

        // Modifying update
        setTimeout(function () {
          d2.update({ a: 1 }, { $set: { b: 2 } }, {})
          // eslint-disable-next-line node/handle-callback-err
          d2.findOne({ a: 1 }, function (err, doc) {
            doc.createdAt.getTime().should.equal(createdAt)
            assert.isBelow(Date.now() - doc.updatedAt.getTime(), 5)

            // Complete replacement
            setTimeout(function () {
              d2.update({ a: 1 }, { c: 3 }, {})
              // eslint-disable-next-line node/handle-callback-err
              d2.findOne({ c: 3 }, function (err, doc) {
                doc.createdAt.getTime().should.equal(createdAt)
                assert.isBelow(Date.now() - doc.updatedAt.getTime(), 5)

                done()
              })
            }, 20)
          })
        }, 20)
      })
    })

    describe('Callback signature', function () {
      it('Regular update, multi false', function (done) {
        d.insert({ a: 1 })
        d.insert({ a: 2 })

        // returnUpdatedDocs set to false
        d.update({ a: 1 }, { $set: { b: 20 } }, {}, function (err, numAffected, affectedDocuments, upsert) {
          assert.isNull(err)
          numAffected.should.equal(1)
          assert.isNull(affectedDocuments)
          assert.isFalse(upsert)

          // returnUpdatedDocs set to true
          d.update({ a: 1 }, { $set: { b: 21 } }, { returnUpdatedDocs: true }, function (err, numAffected, affectedDocuments, upsert) {
            assert.isNull(err)
            numAffected.should.equal(1)
            affectedDocuments.a.should.equal(1)
            affectedDocuments.b.should.equal(21)
            assert.isFalse(upsert)

            done()
          })
        })
      })

      it('Regular update, multi true', function (done) {
        d.insert({ a: 1 })
        d.insert({ a: 2 })

        // returnUpdatedDocs set to false
        d.update({}, { $set: { b: 20 } }, { multi: true }, function (err, numAffected, affectedDocuments, upsert) {
          assert.isNull(err)
          numAffected.should.equal(2)
          assert.isNull(affectedDocuments)
          assert.isFalse(upsert)

          // returnUpdatedDocs set to true
          d.update({}, { $set: { b: 21 } }, {
            multi: true,
            returnUpdatedDocs: true
          }, function (err, numAffected, affectedDocuments, upsert) {
            assert.isNull(err)
            numAffected.should.equal(2)
            affectedDocuments.length.should.equal(2)
            assert.isFalse(upsert)

            done()
          })
        })
      })

      it('Upsert', function (done) {
        d.insert({ a: 1 })
        d.insert({ a: 2 })

        // Upsert flag not set
        d.update({ a: 3 }, { $set: { b: 20 } }, {}, function (err, numAffected, affectedDocuments, upsert) {
          assert.isNull(err)
          numAffected.should.equal(0)
          assert.isNull(affectedDocuments)
          assert.isFalse(upsert)

          // Upsert flag set
          d.update({ a: 3 }, { $set: { b: 21 } }, { upsert: true }, function (err, numAffected, affectedDocuments, upsert) {
            assert.isNull(err)
            numAffected.should.equal(1)
            affectedDocuments.a.should.equal(3)
            affectedDocuments.b.should.equal(21)
            upsert.should.equal(true)

            // eslint-disable-next-line node/handle-callback-err
            d.find({}, function (err, docs) {
              docs.length.should.equal(3)
              done()
            })
          })
        })
      })
    }) // ==== End of 'Update - Callback signature' ==== //
  }) // ==== End of 'Update' ==== //

  describe('Remove', function () {
    it('Can remove multiple documents', function (done) {
      let id1

      // Test DB status
      function testPostUpdateState (cb) {
        // eslint-disable-next-line node/handle-callback-err
        d.find({}, function (err, docs) {
          docs.length.should.equal(1)

          Object.keys(docs[0]).length.should.equal(2)
          docs[0]._id.should.equal(id1)
          docs[0].somedata.should.equal('ok')

          return cb()
        })
      }

      // Actually launch the test
      waterfall([
        function (cb) {
          // eslint-disable-next-line node/handle-callback-err
          d.insert({ somedata: 'ok' }, function (err, doc1) {
            id1 = doc1._id
            // eslint-disable-next-line node/handle-callback-err
            d.insert({ somedata: 'again', plus: 'additional data' }, function (err, doc2) {
              d.insert({ somedata: 'again' }, function (err, doc3) {
                return cb(err)
              })
            })
          })
        },
        function (cb) { // Test with query that doesn't match anything
          d.remove({ somedata: 'again' }, { multi: true }, function (err, n) {
            assert.isNull(err)
            n.should.equal(2)
            return cb()
          })
        },
        apply(testPostUpdateState),
        function (cb) {
          d.loadDatabase(function (err) { return cb(err) })
        },
        apply(testPostUpdateState)
      ], done)
    })

    // This tests concurrency issues
    it('Remove can be called multiple times in parallel and everything that needs to be removed will be', function (done) {
      d.insert({ planet: 'Earth' }, function () {
        d.insert({ planet: 'Mars' }, function () {
          d.insert({ planet: 'Saturn' }, function () {
            // eslint-disable-next-line node/handle-callback-err
            d.find({}, function (err, docs) {
              docs.length.should.equal(3)

              // Remove two docs simultaneously
              const toRemove = ['Mars', 'Saturn']
              each(toRemove, function (planet, cb) {
                d.remove({ planet: planet }, function (err) { return cb(err) })
                // eslint-disable-next-line node/handle-callback-err
              }, function (err) {
                // eslint-disable-next-line node/handle-callback-err
                d.find({}, function (err, docs) {
                  docs.length.should.equal(1)

                  done()
                })
              })
            })
          })
        })
      })
    })

    it('Returns an error if the query is not well formed', function (done) {
      d.insert({ hello: 'world' }, function () {
        d.remove({ $or: { hello: 'world' } }, {}, function (err, nr, upsert) {
          assert.isDefined(err)
          assert.isUndefined(nr)
          assert.isUndefined(upsert)

          done()
        })
      })
    })

    it('Non-multi removes are persistent', function (done) {
      // eslint-disable-next-line node/handle-callback-err
      d.insert({ a: 1, hello: 'world' }, function (err, doc1) {
        // eslint-disable-next-line node/handle-callback-err
        d.insert({ a: 2, hello: 'earth' }, function (err, doc2) {
          // eslint-disable-next-line node/handle-callback-err
          d.insert({ a: 3, hello: 'moto' }, function (err, doc3) {
            d.remove({ a: 2 }, {}, function (err) {
              assert.isNull(err)

              // eslint-disable-next-line node/handle-callback-err
              d.find({}, function (err, docs) {
                docs.sort(function (a, b) { return a.a - b.a })
                docs.length.should.equal(2)
                assert.deepStrictEqual(docs[0], { _id: doc1._id, a: 1, hello: 'world' })
                assert.deepStrictEqual(docs[1], { _id: doc3._id, a: 3, hello: 'moto' })

                // Even after a reload the database state hasn't changed
                d.loadDatabase(function (err) {
                  assert.isNull(err)

                  // eslint-disable-next-line node/handle-callback-err
                  d.find({}, function (err, docs) {
                    docs.sort(function (a, b) { return a.a - b.a })
                    docs.length.should.equal(2)
                    assert.deepStrictEqual(docs[0], { _id: doc1._id, a: 1, hello: 'world' })
                    assert.deepStrictEqual(docs[1], { _id: doc3._id, a: 3, hello: 'moto' })

                    done()
                  })
                })
              })
            })
          })
        })
      })
    })

    it('Multi removes are persistent', function (done) {
      // eslint-disable-next-line node/handle-callback-err
      d.insert({ a: 1, hello: 'world' }, function (err, doc1) {
        // eslint-disable-next-line node/handle-callback-err
        d.insert({ a: 2, hello: 'earth' }, function (err, doc2) {
          // eslint-disable-next-line node/handle-callback-err
          d.insert({ a: 3, hello: 'moto' }, function (err, doc3) {
            d.remove({ a: { $in: [1, 3] } }, { multi: true }, function (err) {
              assert.isNull(err)

              // eslint-disable-next-line node/handle-callback-err
              d.find({}, function (err, docs) {
                docs.length.should.equal(1)
                assert.deepStrictEqual(docs[0], { _id: doc2._id, a: 2, hello: 'earth' })

                // Even after a reload the database state hasn't changed
                d.loadDatabase(function (err) {
                  assert.isNull(err)

                  // eslint-disable-next-line node/handle-callback-err
                  d.find({}, function (err, docs) {
                    docs.length.should.equal(1)
                    assert.deepStrictEqual(docs[0], { _id: doc2._id, a: 2, hello: 'earth' })

                    done()
                  })
                })
              })
            })
          })
        })
      })
    })

    it('Can remove without the options arg (will use defaults then)', function (done) {
      // eslint-disable-next-line node/handle-callback-err
      d.insert({ a: 1, hello: 'world' }, function (err, doc1) {
        // eslint-disable-next-line node/handle-callback-err
        d.insert({ a: 2, hello: 'earth' }, function (err, doc2) {
          // eslint-disable-next-line node/handle-callback-err
          d.insert({ a: 5, hello: 'pluton' }, function (err, doc3) {
            d.remove({ a: 2 }, function (err, nr) {
              assert.isNull(err)
              nr.should.equal(1)
              // eslint-disable-next-line node/handle-callback-err
              d.find({}, function (err, docs) {
                const d1 = docs.find(function (doc) { return doc._id === doc1._id })
                const d2 = docs.find(function (doc) { return doc._id === doc2._id })
                const d3 = docs.find(function (doc) { return doc._id === doc3._id })

                d1.a.should.equal(1)
                assert.isUndefined(d2)
                d3.a.should.equal(5)

                done()
              })
            })
          })
        })
      })
    })
  }) // ==== End of 'Remove' ==== //

  describe('Using indexes', function () {
    describe('ensureIndex and index initialization in database loading', function () {
      it('ensureIndex can be called right after a loadDatabase and be initialized and filled correctly', function (done) {
        const now = new Date()
        const rawData = model.serialize({ _id: 'aaa', z: '1', a: 2, ages: [1, 5, 12] }) + '\n' +
          model.serialize({ _id: 'bbb', z: '2', hello: 'world' }) + '\n' +
          model.serialize({ _id: 'ccc', z: '3', nested: { today: now } })

        d.getAllData().length.should.equal(0)

        fs.writeFile(testDb, rawData, 'utf8', function () {
          d.loadDatabase(function () {
            d.getAllData().length.should.equal(3)

            assert.deepStrictEqual(Object.keys(d.indexes), ['_id'])

            d.ensureIndex({ fieldName: 'z' })
            d.indexes.z.fieldName.should.equal('z')
            d.indexes.z.unique.should.equal(false)
            d.indexes.z.sparse.should.equal(false)
            d.indexes.z.tree.getNumberOfKeys().should.equal(3)
            d.indexes.z.tree.search('1')[0].should.equal(d.getAllData()[0])
            d.indexes.z.tree.search('2')[0].should.equal(d.getAllData()[1])
            d.indexes.z.tree.search('3')[0].should.equal(d.getAllData()[2])

            done()
          })
        })
      })

      it('ensureIndex can be called twice on the same field, the second call will have no effect', function (done) {
        Object.keys(d.indexes).length.should.equal(1)
        Object.keys(d.indexes)[0].should.equal('_id')

        d.insert({ planet: 'Earth' }, function () {
          d.insert({ planet: 'Mars' }, function () {
            // eslint-disable-next-line node/handle-callback-err
            d.find({}, function (err, docs) {
              docs.length.should.equal(2)

              d.ensureIndex({ fieldName: 'planet' }, function (err) {
                assert.isNull(err)
                Object.keys(d.indexes).length.should.equal(2)
                Object.keys(d.indexes)[0].should.equal('_id')
                Object.keys(d.indexes)[1].should.equal('planet')

                d.indexes.planet.getAll().length.should.equal(2)

                // This second call has no effect, documents don't get inserted twice in the index
                d.ensureIndex({ fieldName: 'planet' }, function (err) {
                  assert.isNull(err)
                  Object.keys(d.indexes).length.should.equal(2)
                  Object.keys(d.indexes)[0].should.equal('_id')
                  Object.keys(d.indexes)[1].should.equal('planet')

                  d.indexes.planet.getAll().length.should.equal(2)

                  done()
                })
              })
            })
          })
        })
      })

      it('ensureIndex can be called twice on the same compound fields, the second call will have no effect', function (done) {
        Object.keys(d.indexes).length.should.equal(1)
        Object.keys(d.indexes)[0].should.equal('_id')

        d.insert({ star: 'sun', planet: 'Earth' }, function () {
          d.insert({ star: 'sun', planet: 'Mars' }, function () {
            // eslint-disable-next-line node/handle-callback-err
            d.find({}, function (err, docs) {
              docs.length.should.equal(2)

              d.ensureIndex({ fieldName: ['star', 'planet'] }, function (err) {
                assert.isNull(err)
                Object.keys(d.indexes).length.should.equal(2)
                Object.keys(d.indexes)[0].should.equal('_id')
                Object.keys(d.indexes)[1].should.equal('planet,star')

                d.indexes['planet,star'].getAll().length.should.equal(2)

                // This second call has no effect, documents don't get inserted twice in the index
                d.ensureIndex({ fieldName: ['star', 'planet'] }, function (err) {
                  assert.isNull(err)
                  Object.keys(d.indexes).length.should.equal(2)
                  Object.keys(d.indexes)[0].should.equal('_id')
                  Object.keys(d.indexes)[1].should.equal('planet,star')

                  d.indexes['planet,star'].getAll().length.should.equal(2)

                  done()
                })
              })
            })
          })
        })
      })

      it('ensureIndex can be called twice on the same compound fields with a different order, the second call will have no effect', function (done) {
        Object.keys(d.indexes).length.should.equal(1)
        Object.keys(d.indexes)[0].should.equal('_id')

        d.insert({ star: 'sun', planet: 'Earth' }, function () {
          d.insert({ star: 'sun', planet: 'Mars' }, function () {
            // eslint-disable-next-line node/handle-callback-err
            d.find({}, function (err, docs) {
              docs.length.should.equal(2)

              d.ensureIndex({ fieldName: ['star', 'planet'] }, function (err) {
                assert.isNull(err)
                Object.keys(d.indexes).length.should.equal(2)
                Object.keys(d.indexes)[0].should.equal('_id')
                Object.keys(d.indexes)[1].should.equal('planet,star')

                d.indexes['planet,star'].getAll().length.should.equal(2)

                // This second call has no effect, documents don't get inserted twice in the index
                d.ensureIndex({ fieldName: ['planet', 'star'] }, function (err) {
                  assert.isNull(err)
                  Object.keys(d.indexes).length.should.equal(2)
                  Object.keys(d.indexes)[0].should.equal('_id')
                  Object.keys(d.indexes)[1].should.equal('planet,star')

                  d.indexes['planet,star'].getAll().length.should.equal(2)

                  done()
                })
              })
            })
          })
        })
      })

      it('ensureIndex cannot be called with an illegal field name', function (done) {
        d.ensureIndex({ fieldName: 'star,planet' }, function (err) {
          assert.isNotNull(err)
          d.ensureIndex({ fieldName: ['star,planet', 'other'] }, function (err) {
            assert.isNotNull(err)
            done()
          })
        })
      })

      it('ensureIndex can be called after the data set was modified and the index still be correct', function (done) {
        const rawData = model.serialize({ _id: 'aaa', z: '1', a: 2, ages: [1, 5, 12] }) + '\n' +
          model.serialize({ _id: 'bbb', z: '2', hello: 'world' })

        d.getAllData().length.should.equal(0)

        fs.writeFile(testDb, rawData, 'utf8', function () {
          d.loadDatabase(function () {
            d.getAllData().length.should.equal(2)

            assert.deepStrictEqual(Object.keys(d.indexes), ['_id'])

            // eslint-disable-next-line node/handle-callback-err
            d.insert({ z: '12', yes: 'yes' }, function (err, newDoc1) {
              // eslint-disable-next-line node/handle-callback-err
              d.insert({ z: '14', nope: 'nope' }, function (err, newDoc2) {
                d.remove({ z: '2' }, {}, function () {
                  d.update({ z: '1' }, { $set: { yes: 'yep' } }, {}, function () {
                    assert.deepStrictEqual(Object.keys(d.indexes), ['_id'])

                    d.ensureIndex({ fieldName: 'z' })
                    d.indexes.z.fieldName.should.equal('z')
                    d.indexes.z.unique.should.equal(false)
                    d.indexes.z.sparse.should.equal(false)
                    d.indexes.z.tree.getNumberOfKeys().should.equal(3)

                    // The pointers in the _id and z indexes are the same
                    d.indexes.z.tree.search('1')[0].should.equal(d.indexes._id.getMatching('aaa')[0])
                    d.indexes.z.tree.search('12')[0].should.equal(d.indexes._id.getMatching(newDoc1._id)[0])
                    d.indexes.z.tree.search('14')[0].should.equal(d.indexes._id.getMatching(newDoc2._id)[0])

                    // The data in the z index is correct
                    // eslint-disable-next-line node/handle-callback-err
                    d.find({}, function (err, docs) {
                      const doc0 = docs.find(function (doc) { return doc._id === 'aaa' })
                      const doc1 = docs.find(function (doc) { return doc._id === newDoc1._id })
                      const doc2 = docs.find(function (doc) { return doc._id === newDoc2._id })

                      docs.length.should.equal(3)

                      assert.deepStrictEqual(doc0, { _id: 'aaa', z: '1', a: 2, ages: [1, 5, 12], yes: 'yep' })
                      assert.deepStrictEqual(doc1, { _id: newDoc1._id, z: '12', yes: 'yes' })
                      assert.deepStrictEqual(doc2, { _id: newDoc2._id, z: '14', nope: 'nope' })

                      done()
                    })
                  })
                })
              })
            })
          })
        })
      })

      it('ensureIndex can be called before a loadDatabase and still be initialized and filled correctly', function (done) {
        const now = new Date()
        const rawData = model.serialize({ _id: 'aaa', z: '1', a: 2, ages: [1, 5, 12] }) + '\n' +
          model.serialize({ _id: 'bbb', z: '2', hello: 'world' }) + '\n' +
          model.serialize({ _id: 'ccc', z: '3', nested: { today: now } })

        d.getAllData().length.should.equal(0)

        d.ensureIndex({ fieldName: 'z' }, function () {
          d.indexes.z.fieldName.should.equal('z')
          d.indexes.z.unique.should.equal(false)
          d.indexes.z.sparse.should.equal(false)
          d.indexes.z.tree.getNumberOfKeys().should.equal(0)

          fs.writeFile(testDb, rawData, 'utf8', function () {
            d.loadDatabase(function () {
              const doc1 = d.getAllData().find(function (doc) { return doc.z === '1' })
              const doc2 = d.getAllData().find(function (doc) { return doc.z === '2' })
              const doc3 = d.getAllData().find(function (doc) { return doc.z === '3' })

              d.getAllData().length.should.equal(3)

              d.indexes.z.tree.getNumberOfKeys().should.equal(3)
              d.indexes.z.tree.search('1')[0].should.equal(doc1)
              d.indexes.z.tree.search('2')[0].should.equal(doc2)
              d.indexes.z.tree.search('3')[0].should.equal(doc3)

              done()
            })
          })
        })
      })

      it('Can initialize multiple indexes on a database load', function (done) {
        const now = new Date()
        const rawData = model.serialize({ _id: 'aaa', z: '1', a: 2, ages: [1, 5, 12] }) + '\n' +
          model.serialize({ _id: 'bbb', z: '2', a: 'world' }) + '\n' +
          model.serialize({ _id: 'ccc', z: '3', a: { today: now } })

        d.getAllData().length.should.equal(0)
        d.ensureIndex({ fieldName: 'z' }, function () {
          d.ensureIndex({ fieldName: 'a' }, function () {
            d.indexes.a.tree.getNumberOfKeys().should.equal(0)
            d.indexes.z.tree.getNumberOfKeys().should.equal(0)

            fs.writeFile(testDb, rawData, 'utf8', function () {
              d.loadDatabase(function (err) {
                const doc1 = d.getAllData().find(function (doc) { return doc.z === '1' })
                const doc2 = d.getAllData().find(function (doc) { return doc.z === '2' })
                const doc3 = d.getAllData().find(function (doc) { return doc.z === '3' })

                assert.isNull(err)
                d.getAllData().length.should.equal(3)

                d.indexes.z.tree.getNumberOfKeys().should.equal(3)
                d.indexes.z.tree.search('1')[0].should.equal(doc1)
                d.indexes.z.tree.search('2')[0].should.equal(doc2)
                d.indexes.z.tree.search('3')[0].should.equal(doc3)

                d.indexes.a.tree.getNumberOfKeys().should.equal(3)
                d.indexes.a.tree.search(2)[0].should.equal(doc1)
                d.indexes.a.tree.search('world')[0].should.equal(doc2)
                d.indexes.a.tree.search({ today: now })[0].should.equal(doc3)

                done()
              })
            })
          })
        })
      })

      it('If a unique constraint is not respected, database loading will not work and no data will be inserted', function (done) {
        const now = new Date()
        const rawData = model.serialize({ _id: 'aaa', z: '1', a: 2, ages: [1, 5, 12] }) + '\n' +
          model.serialize({ _id: 'bbb', z: '2', a: 'world' }) + '\n' +
          model.serialize({ _id: 'ccc', z: '1', a: { today: now } })

        d.getAllData().length.should.equal(0)

        d.ensureIndex({ fieldName: 'z', unique: true }, function () {
          d.indexes.z.tree.getNumberOfKeys().should.equal(0)

          fs.writeFile(testDb, rawData, 'utf8', function () {
            d.loadDatabase(function (err) {
              assert.isNotNull(err)
              err.errorType.should.equal('uniqueViolated')
              err.key.should.equal('1')
              d.getAllData().length.should.equal(0)
              d.indexes.z.tree.getNumberOfKeys().should.equal(0)

              done()
            })
          })
        })
      })

      it('If a unique constraint is not respected, ensureIndex will return an error and not create an index', function (done) {
        d.insert({ a: 1, b: 4 }, function () {
          d.insert({ a: 2, b: 45 }, function () {
            d.insert({ a: 1, b: 3 }, function () {
              d.ensureIndex({ fieldName: 'b' }, function (err) {
                assert.isNull(err)

                d.ensureIndex({ fieldName: 'a', unique: true }, function (err) {
                  err.errorType.should.equal('uniqueViolated')
                  assert.deepStrictEqual(Object.keys(d.indexes), ['_id', 'b'])

                  done()
                })
              })
            })
          })
        })
      })

      it('Can remove an index', function (done) {
        d.ensureIndex({ fieldName: 'e' }, function (err) {
          assert.isNull(err)

          Object.keys(d.indexes).length.should.equal(2)
          assert.isNotNull(d.indexes.e)

          d.removeIndex('e', function (err) {
            assert.isNull(err)
            Object.keys(d.indexes).length.should.equal(1)
            assert.isUndefined(d.indexes.e)

            done()
          })
        })
      })
    }) // ==== End of 'ensureIndex and index initialization in database loading' ==== //

    describe('Indexing newly inserted documents', function () {
      it('Newly inserted documents are indexed', function (done) {
        d.ensureIndex({ fieldName: 'z' })
        d.indexes.z.tree.getNumberOfKeys().should.equal(0)

        // eslint-disable-next-line node/handle-callback-err
        d.insert({ a: 2, z: 'yes' }, function (err, newDoc) {
          d.indexes.z.tree.getNumberOfKeys().should.equal(1)
          assert.deepStrictEqual(d.indexes.z.getMatching('yes'), [newDoc])

          // eslint-disable-next-line node/handle-callback-err
          d.insert({ a: 5, z: 'nope' }, function (err, newDoc) {
            d.indexes.z.tree.getNumberOfKeys().should.equal(2)
            assert.deepStrictEqual(d.indexes.z.getMatching('nope'), [newDoc])

            done()
          })
        })
      })

      it('If multiple indexes are defined, the document is inserted in all of them', function (done) {
        d.ensureIndex({ fieldName: 'z' })
        d.ensureIndex({ fieldName: 'ya' })
        d.indexes.z.tree.getNumberOfKeys().should.equal(0)

        // eslint-disable-next-line node/handle-callback-err
        d.insert({ a: 2, z: 'yes', ya: 'indeed' }, function (err, newDoc) {
          d.indexes.z.tree.getNumberOfKeys().should.equal(1)
          d.indexes.ya.tree.getNumberOfKeys().should.equal(1)
          assert.deepStrictEqual(d.indexes.z.getMatching('yes'), [newDoc])
          assert.deepStrictEqual(d.indexes.ya.getMatching('indeed'), [newDoc])

          // eslint-disable-next-line node/handle-callback-err
          d.insert({ a: 5, z: 'nope', ya: 'sure' }, function (err, newDoc2) {
            d.indexes.z.tree.getNumberOfKeys().should.equal(2)
            d.indexes.ya.tree.getNumberOfKeys().should.equal(2)
            assert.deepStrictEqual(d.indexes.z.getMatching('nope'), [newDoc2])
            assert.deepStrictEqual(d.indexes.ya.getMatching('sure'), [newDoc2])

            done()
          })
        })
      })

      it('Can insert two docs at the same key for a non unique index', function (done) {
        d.ensureIndex({ fieldName: 'z' })
        d.indexes.z.tree.getNumberOfKeys().should.equal(0)

        // eslint-disable-next-line node/handle-callback-err
        d.insert({ a: 2, z: 'yes' }, function (err, newDoc) {
          d.indexes.z.tree.getNumberOfKeys().should.equal(1)
          assert.deepStrictEqual(d.indexes.z.getMatching('yes'), [newDoc])

          // eslint-disable-next-line node/handle-callback-err
          d.insert({ a: 5, z: 'yes' }, function (err, newDoc2) {
            d.indexes.z.tree.getNumberOfKeys().should.equal(1)
            assert.deepStrictEqual(d.indexes.z.getMatching('yes'), [newDoc, newDoc2])

            done()
          })
        })
      })

      it('If the index has a unique constraint, an error is thrown if it is violated and the data is not modified', function (done) {
        d.ensureIndex({ fieldName: 'z', unique: true })
        d.indexes.z.tree.getNumberOfKeys().should.equal(0)

        // eslint-disable-next-line node/handle-callback-err
        d.insert({ a: 2, z: 'yes' }, function (err, newDoc) {
          d.indexes.z.tree.getNumberOfKeys().should.equal(1)
          assert.deepStrictEqual(d.indexes.z.getMatching('yes'), [newDoc])

          d.insert({ a: 5, z: 'yes' }, function (err) {
            err.errorType.should.equal('uniqueViolated')
            err.key.should.equal('yes')

            // Index didn't change
            d.indexes.z.tree.getNumberOfKeys().should.equal(1)
            assert.deepStrictEqual(d.indexes.z.getMatching('yes'), [newDoc])

            // Data didn't change
            assert.deepStrictEqual(d.getAllData(), [newDoc])
            d.loadDatabase(function () {
              d.getAllData().length.should.equal(1)
              assert.deepStrictEqual(d.getAllData()[0], newDoc)

              done()
            })
          })
        })
      })

      it('If an index has a unique constraint, other indexes cannot be modified when it raises an error', function (done) {
        d.ensureIndex({ fieldName: 'nonu1' })
        d.ensureIndex({ fieldName: 'uni', unique: true })
        d.ensureIndex({ fieldName: 'nonu2' })

        d.insert({ nonu1: 'yes', nonu2: 'yes2', uni: 'willfail' }, function (err, newDoc) {
          assert.isNull(err)
          d.indexes.nonu1.tree.getNumberOfKeys().should.equal(1)
          d.indexes.uni.tree.getNumberOfKeys().should.equal(1)
          d.indexes.nonu2.tree.getNumberOfKeys().should.equal(1)

          d.insert({ nonu1: 'no', nonu2: 'no2', uni: 'willfail' }, function (err) {
            err.errorType.should.equal('uniqueViolated')

            // No index was modified
            d.indexes.nonu1.tree.getNumberOfKeys().should.equal(1)
            d.indexes.uni.tree.getNumberOfKeys().should.equal(1)
            d.indexes.nonu2.tree.getNumberOfKeys().should.equal(1)

            assert.deepStrictEqual(d.indexes.nonu1.getMatching('yes'), [newDoc])
            assert.deepStrictEqual(d.indexes.uni.getMatching('willfail'), [newDoc])
            assert.deepStrictEqual(d.indexes.nonu2.getMatching('yes2'), [newDoc])

            done()
          })
        })
      })

      it('Unique indexes prevent you from inserting two docs where the field is undefined except if theyre sparse', function (done) {
        d.ensureIndex({ fieldName: 'zzz', unique: true })
        d.indexes.zzz.tree.getNumberOfKeys().should.equal(0)

        // eslint-disable-next-line node/handle-callback-err
        d.insert({ a: 2, z: 'yes' }, function (err, newDoc) {
          d.indexes.zzz.tree.getNumberOfKeys().should.equal(1)
          assert.deepStrictEqual(d.indexes.zzz.getMatching(undefined), [newDoc])

          d.insert({ a: 5, z: 'other' }, function (err) {
            err.errorType.should.equal('uniqueViolated')
            assert.isUndefined(err.key)

            d.ensureIndex({ fieldName: 'yyy', unique: true, sparse: true })

            d.insert({ a: 5, z: 'other', zzz: 'set' }, function (err) {
              assert.isNull(err)
              d.indexes.yyy.getAll().length.should.equal(0) // Nothing indexed
              d.indexes.zzz.getAll().length.should.equal(2)

              done()
            })
          })
        })
      })

      it('Insertion still works as before with indexing', function (done) {
        d.ensureIndex({ fieldName: 'a' })
        d.ensureIndex({ fieldName: 'b' })

        // eslint-disable-next-line node/handle-callback-err
        d.insert({ a: 1, b: 'hello' }, function (err, doc1) {
          // eslint-disable-next-line node/handle-callback-err
          d.insert({ a: 2, b: 'si' }, function (err, doc2) {
            // eslint-disable-next-line node/handle-callback-err
            d.find({}, function (err, docs) {
              assert.deepStrictEqual(doc1, docs.find(function (d) { return d._id === doc1._id }))
              assert.deepStrictEqual(doc2, docs.find(function (d) { return d._id === doc2._id }))

              done()
            })
          })
        })
      })

      it('All indexes point to the same data as the main index on _id', function (done) {
        d.ensureIndex({ fieldName: 'a' })

        // eslint-disable-next-line node/handle-callback-err
        d.insert({ a: 1, b: 'hello' }, function (err, doc1) {
          // eslint-disable-next-line node/handle-callback-err
          d.insert({ a: 2, b: 'si' }, function (err, doc2) {
            // eslint-disable-next-line node/handle-callback-err
            d.find({}, function (err, docs) {
              docs.length.should.equal(2)
              d.getAllData().length.should.equal(2)

              d.indexes._id.getMatching(doc1._id).length.should.equal(1)
              d.indexes.a.getMatching(1).length.should.equal(1)
              d.indexes._id.getMatching(doc1._id)[0].should.equal(d.indexes.a.getMatching(1)[0])

              d.indexes._id.getMatching(doc2._id).length.should.equal(1)
              d.indexes.a.getMatching(2).length.should.equal(1)
              d.indexes._id.getMatching(doc2._id)[0].should.equal(d.indexes.a.getMatching(2)[0])

              done()
            })
          })
        })
      })

      it('If a unique constraint is violated, no index is changed, including the main one', function (done) {
        d.ensureIndex({ fieldName: 'a', unique: true })

        // eslint-disable-next-line node/handle-callback-err
        d.insert({ a: 1, b: 'hello' }, function (err, doc1) {
          d.insert({ a: 1, b: 'si' }, function (err) {
            assert.isDefined(err)

            // eslint-disable-next-line node/handle-callback-err
            d.find({}, function (err, docs) {
              docs.length.should.equal(1)
              d.getAllData().length.should.equal(1)

              d.indexes._id.getMatching(doc1._id).length.should.equal(1)
              d.indexes.a.getMatching(1).length.should.equal(1)
              d.indexes._id.getMatching(doc1._id)[0].should.equal(d.indexes.a.getMatching(1)[0])

              d.indexes.a.getMatching(2).length.should.equal(0)

              done()
            })
          })
        })
      })
    }) // ==== End of 'Indexing newly inserted documents' ==== //

    describe('Updating indexes upon document update', function () {
      it('Updating docs still works as before with indexing', function (done) {
        d.ensureIndex({ fieldName: 'a' })

        // eslint-disable-next-line node/handle-callback-err
        d.insert({ a: 1, b: 'hello' }, function (err, _doc1) {
          // eslint-disable-next-line node/handle-callback-err
          d.insert({ a: 2, b: 'si' }, function (err, _doc2) {
            d.update({ a: 1 }, { $set: { a: 456, b: 'no' } }, {}, function (err, nr) {
              const data = d.getAllData()
              const doc1 = data.find(function (doc) { return doc._id === _doc1._id })
              const doc2 = data.find(function (doc) { return doc._id === _doc2._id })

              assert.isNull(err)
              nr.should.equal(1)

              data.length.should.equal(2)
              assert.deepStrictEqual(doc1, { a: 456, b: 'no', _id: _doc1._id })
              assert.deepStrictEqual(doc2, { a: 2, b: 'si', _id: _doc2._id })

              d.update({}, { $inc: { a: 10 }, $set: { b: 'same' } }, { multi: true }, function (err, nr) {
                const data = d.getAllData()
                const doc1 = data.find(function (doc) { return doc._id === _doc1._id })
                const doc2 = data.find(function (doc) { return doc._id === _doc2._id })

                assert.isNull(err)
                nr.should.equal(2)

                data.length.should.equal(2)
                assert.deepStrictEqual(doc1, { a: 466, b: 'same', _id: _doc1._id })
                assert.deepStrictEqual(doc2, { a: 12, b: 'same', _id: _doc2._id })

                done()
              })
            })
          })
        })
      })

      it('Indexes get updated when a document (or multiple documents) is updated', function (done) {
        d.ensureIndex({ fieldName: 'a' })
        d.ensureIndex({ fieldName: 'b' })

        // eslint-disable-next-line node/handle-callback-err
        d.insert({ a: 1, b: 'hello' }, function (err, doc1) {
          // eslint-disable-next-line node/handle-callback-err
          d.insert({ a: 2, b: 'si' }, function (err, doc2) {
            // Simple update
            d.update({ a: 1 }, { $set: { a: 456, b: 'no' } }, {}, function (err, nr) {
              assert.isNull(err)
              nr.should.equal(1)

              d.indexes.a.tree.getNumberOfKeys().should.equal(2)
              d.indexes.a.getMatching(456)[0]._id.should.equal(doc1._id)
              d.indexes.a.getMatching(2)[0]._id.should.equal(doc2._id)

              d.indexes.b.tree.getNumberOfKeys().should.equal(2)
              d.indexes.b.getMatching('no')[0]._id.should.equal(doc1._id)
              d.indexes.b.getMatching('si')[0]._id.should.equal(doc2._id)

              // The same pointers are shared between all indexes
              d.indexes.a.tree.getNumberOfKeys().should.equal(2)
              d.indexes.b.tree.getNumberOfKeys().should.equal(2)
              d.indexes._id.tree.getNumberOfKeys().should.equal(2)
              d.indexes.a.getMatching(456)[0].should.equal(d.indexes._id.getMatching(doc1._id)[0])
              d.indexes.b.getMatching('no')[0].should.equal(d.indexes._id.getMatching(doc1._id)[0])
              d.indexes.a.getMatching(2)[0].should.equal(d.indexes._id.getMatching(doc2._id)[0])
              d.indexes.b.getMatching('si')[0].should.equal(d.indexes._id.getMatching(doc2._id)[0])

              // Multi update
              d.update({}, { $inc: { a: 10 }, $set: { b: 'same' } }, { multi: true }, function (err, nr) {
                assert.isNull(err)
                nr.should.equal(2)

                d.indexes.a.tree.getNumberOfKeys().should.equal(2)
                d.indexes.a.getMatching(466)[0]._id.should.equal(doc1._id)
                d.indexes.a.getMatching(12)[0]._id.should.equal(doc2._id)

                d.indexes.b.tree.getNumberOfKeys().should.equal(1)
                d.indexes.b.getMatching('same').length.should.equal(2)
                d.indexes.b.getMatching('same').map(x => x._id).should.contain(doc1._id)
                d.indexes.b.getMatching('same').map(x => x._id).should.contain(doc2._id)

                // The same pointers are shared between all indexes
                d.indexes.a.tree.getNumberOfKeys().should.equal(2)
                d.indexes.b.tree.getNumberOfKeys().should.equal(1)
                d.indexes.b.getAll().length.should.equal(2)
                d.indexes._id.tree.getNumberOfKeys().should.equal(2)
                d.indexes.a.getMatching(466)[0].should.equal(d.indexes._id.getMatching(doc1._id)[0])
                d.indexes.a.getMatching(12)[0].should.equal(d.indexes._id.getMatching(doc2._id)[0])
                // Can't test the pointers in b as their order is randomized, but it is the same as with a

                done()
              })
            })
          })
        })
      })

      it('If a simple update violates a contraint, all changes are rolled back and an error is thrown', function (done) {
        d.ensureIndex({ fieldName: 'a', unique: true })
        d.ensureIndex({ fieldName: 'b', unique: true })
        d.ensureIndex({ fieldName: 'c', unique: true })

        // eslint-disable-next-line node/handle-callback-err
        d.insert({ a: 1, b: 10, c: 100 }, function (err, _doc1) {
          // eslint-disable-next-line node/handle-callback-err
          d.insert({ a: 2, b: 20, c: 200 }, function (err, _doc2) {
            // eslint-disable-next-line node/handle-callback-err
            d.insert({ a: 3, b: 30, c: 300 }, function (err, _doc3) {
              // Will conflict with doc3
              d.update({ a: 2 }, { $inc: { a: 10, c: 1000 }, $set: { b: 30 } }, {}, function (err) {
                const data = d.getAllData()
                const doc1 = data.find(function (doc) { return doc._id === _doc1._id })
                const doc2 = data.find(function (doc) { return doc._id === _doc2._id })
                const doc3 = data.find(function (doc) { return doc._id === _doc3._id })

                err.errorType.should.equal('uniqueViolated')

                // Data left unchanged
                data.length.should.equal(3)
                assert.deepStrictEqual(doc1, { a: 1, b: 10, c: 100, _id: _doc1._id })
                assert.deepStrictEqual(doc2, { a: 2, b: 20, c: 200, _id: _doc2._id })
                assert.deepStrictEqual(doc3, { a: 3, b: 30, c: 300, _id: _doc3._id })

                // All indexes left unchanged and pointing to the same docs
                d.indexes.a.tree.getNumberOfKeys().should.equal(3)
                d.indexes.a.getMatching(1)[0].should.equal(doc1)
                d.indexes.a.getMatching(2)[0].should.equal(doc2)
                d.indexes.a.getMatching(3)[0].should.equal(doc3)

                d.indexes.b.tree.getNumberOfKeys().should.equal(3)
                d.indexes.b.getMatching(10)[0].should.equal(doc1)
                d.indexes.b.getMatching(20)[0].should.equal(doc2)
                d.indexes.b.getMatching(30)[0].should.equal(doc3)

                d.indexes.c.tree.getNumberOfKeys().should.equal(3)
                d.indexes.c.getMatching(100)[0].should.equal(doc1)
                d.indexes.c.getMatching(200)[0].should.equal(doc2)
                d.indexes.c.getMatching(300)[0].should.equal(doc3)

                done()
              })
            })
          })
        })
      })

      it('If a multi update violates a contraint, all changes are rolled back and an error is thrown', function (done) {
        d.ensureIndex({ fieldName: 'a', unique: true })
        d.ensureIndex({ fieldName: 'b', unique: true })
        d.ensureIndex({ fieldName: 'c', unique: true })

        // eslint-disable-next-line node/handle-callback-err
        d.insert({ a: 1, b: 10, c: 100 }, function (err, _doc1) {
          // eslint-disable-next-line node/handle-callback-err
          d.insert({ a: 2, b: 20, c: 200 }, function (err, _doc2) {
            // eslint-disable-next-line node/handle-callback-err
            d.insert({ a: 3, b: 30, c: 300 }, function (err, _doc3) {
              // Will conflict with doc3
              d.update({ a: { $in: [1, 2] } }, {
                $inc: { a: 10, c: 1000 },
                $set: { b: 30 }
              }, { multi: true }, function (err) {
                const data = d.getAllData()
                const doc1 = data.find(function (doc) { return doc._id === _doc1._id })
                const doc2 = data.find(function (doc) { return doc._id === _doc2._id })
                const doc3 = data.find(function (doc) { return doc._id === _doc3._id })

                err.errorType.should.equal('uniqueViolated')

                // Data left unchanged
                data.length.should.equal(3)
                assert.deepStrictEqual(doc1, { a: 1, b: 10, c: 100, _id: _doc1._id })
                assert.deepStrictEqual(doc2, { a: 2, b: 20, c: 200, _id: _doc2._id })
                assert.deepStrictEqual(doc3, { a: 3, b: 30, c: 300, _id: _doc3._id })

                // All indexes left unchanged and pointing to the same docs
                d.indexes.a.tree.getNumberOfKeys().should.equal(3)
                d.indexes.a.getMatching(1)[0].should.equal(doc1)
                d.indexes.a.getMatching(2)[0].should.equal(doc2)
                d.indexes.a.getMatching(3)[0].should.equal(doc3)

                d.indexes.b.tree.getNumberOfKeys().should.equal(3)
                d.indexes.b.getMatching(10)[0].should.equal(doc1)
                d.indexes.b.getMatching(20)[0].should.equal(doc2)
                d.indexes.b.getMatching(30)[0].should.equal(doc3)

                d.indexes.c.tree.getNumberOfKeys().should.equal(3)
                d.indexes.c.getMatching(100)[0].should.equal(doc1)
                d.indexes.c.getMatching(200)[0].should.equal(doc2)
                d.indexes.c.getMatching(300)[0].should.equal(doc3)

                done()
              })
            })
          })
        })
      })
    }) // ==== End of 'Updating indexes upon document update' ==== //

    describe('Updating indexes upon document remove', function () {
      it('Removing docs still works as before with indexing', function (done) {
        d.ensureIndex({ fieldName: 'a' })

        // eslint-disable-next-line node/handle-callback-err
        d.insert({ a: 1, b: 'hello' }, function (err, _doc1) {
          // eslint-disable-next-line node/handle-callback-err
          d.insert({ a: 2, b: 'si' }, function (err, _doc2) {
            // eslint-disable-next-line node/handle-callback-err
            d.insert({ a: 3, b: 'coin' }, function (err, _doc3) {
              d.remove({ a: 1 }, {}, function (err, nr) {
                const data = d.getAllData()
                const doc2 = data.find(function (doc) { return doc._id === _doc2._id })
                const doc3 = data.find(function (doc) { return doc._id === _doc3._id })

                assert.isNull(err)
                nr.should.equal(1)

                data.length.should.equal(2)
                assert.deepStrictEqual(doc2, { a: 2, b: 'si', _id: _doc2._id })
                assert.deepStrictEqual(doc3, { a: 3, b: 'coin', _id: _doc3._id })

                d.remove({ a: { $in: [2, 3] } }, { multi: true }, function (err, nr) {
                  const data = d.getAllData()

                  assert.isNull(err)
                  nr.should.equal(2)
                  data.length.should.equal(0)

                  done()
                })
              })
            })
          })
        })
      })

      it('Indexes get updated when a document (or multiple documents) is removed', function (done) {
        d.ensureIndex({ fieldName: 'a' })
        d.ensureIndex({ fieldName: 'b' })

        // eslint-disable-next-line node/handle-callback-err
        d.insert({ a: 1, b: 'hello' }, function (err, doc1) {
          // eslint-disable-next-line node/handle-callback-err
          d.insert({ a: 2, b: 'si' }, function (err, doc2) {
            // eslint-disable-next-line node/handle-callback-err
            d.insert({ a: 3, b: 'coin' }, function (err, doc3) {
              // Simple remove
              d.remove({ a: 1 }, {}, function (err, nr) {
                assert.isNull(err)
                nr.should.equal(1)

                d.indexes.a.tree.getNumberOfKeys().should.equal(2)
                d.indexes.a.getMatching(2)[0]._id.should.equal(doc2._id)
                d.indexes.a.getMatching(3)[0]._id.should.equal(doc3._id)

                d.indexes.b.tree.getNumberOfKeys().should.equal(2)
                d.indexes.b.getMatching('si')[0]._id.should.equal(doc2._id)
                d.indexes.b.getMatching('coin')[0]._id.should.equal(doc3._id)

                // The same pointers are shared between all indexes
                d.indexes.a.tree.getNumberOfKeys().should.equal(2)
                d.indexes.b.tree.getNumberOfKeys().should.equal(2)
                d.indexes._id.tree.getNumberOfKeys().should.equal(2)
                d.indexes.a.getMatching(2)[0].should.equal(d.indexes._id.getMatching(doc2._id)[0])
                d.indexes.b.getMatching('si')[0].should.equal(d.indexes._id.getMatching(doc2._id)[0])
                d.indexes.a.getMatching(3)[0].should.equal(d.indexes._id.getMatching(doc3._id)[0])
                d.indexes.b.getMatching('coin')[0].should.equal(d.indexes._id.getMatching(doc3._id)[0])

                // Multi remove
                d.remove({}, { multi: true }, function (err, nr) {
                  assert.isNull(err)
                  nr.should.equal(2)

                  d.indexes.a.tree.getNumberOfKeys().should.equal(0)
                  d.indexes.b.tree.getNumberOfKeys().should.equal(0)
                  d.indexes._id.tree.getNumberOfKeys().should.equal(0)

                  done()
                })
              })
            })
          })
        })
      })
    }) // ==== End of 'Updating indexes upon document remove' ==== //

    describe('Persisting indexes', function () {
      it('Indexes are persisted to a separate file and recreated upon reload', function (done) {
        const persDb = 'workspace/persistIndexes.db'
        let db

        if (fs.existsSync(persDb)) { fs.writeFileSync(persDb, '', 'utf8') }
        db = new Datastore({ filename: persDb, autoload: true })

        Object.keys(db.indexes).length.should.equal(1)
        Object.keys(db.indexes)[0].should.equal('_id')

        db.insert({ planet: 'Earth' }, function (err) {
          assert.isNull(err)
          db.insert({ planet: 'Mars' }, function (err) {
            assert.isNull(err)

            // eslint-disable-next-line node/handle-callback-err
            db.ensureIndex({ fieldName: 'planet' }, function (err) {
              Object.keys(db.indexes).length.should.equal(2)
              Object.keys(db.indexes)[0].should.equal('_id')
              Object.keys(db.indexes)[1].should.equal('planet')
              db.indexes._id.getAll().length.should.equal(2)
              db.indexes.planet.getAll().length.should.equal(2)
              db.indexes.planet.fieldName.should.equal('planet')

              // After a reload the indexes are recreated
              db = new Datastore({ filename: persDb })
              db.loadDatabase(function (err) {
                assert.isNull(err)
                Object.keys(db.indexes).length.should.equal(2)
                Object.keys(db.indexes)[0].should.equal('_id')
                Object.keys(db.indexes)[1].should.equal('planet')
                db.indexes._id.getAll().length.should.equal(2)
                db.indexes.planet.getAll().length.should.equal(2)
                db.indexes.planet.fieldName.should.equal('planet')

                // After another reload the indexes are still there (i.e. they are preserved during autocompaction)
                db = new Datastore({ filename: persDb })
                db.loadDatabase(function (err) {
                  assert.isNull(err)
                  Object.keys(db.indexes).length.should.equal(2)
                  Object.keys(db.indexes)[0].should.equal('_id')
                  Object.keys(db.indexes)[1].should.equal('planet')
                  db.indexes._id.getAll().length.should.equal(2)
                  db.indexes.planet.getAll().length.should.equal(2)
                  db.indexes.planet.fieldName.should.equal('planet')

                  done()
                })
              })
            })
          })
        })
      })

      it('Indexes are persisted with their options and recreated even if some db operation happen between loads', function (done) {
        const persDb = 'workspace/persistIndexes.db'
        let db

        if (fs.existsSync(persDb)) { fs.writeFileSync(persDb, '', 'utf8') }
        db = new Datastore({ filename: persDb, autoload: true })

        Object.keys(db.indexes).length.should.equal(1)
        Object.keys(db.indexes)[0].should.equal('_id')

        db.insert({ planet: 'Earth' }, function (err) {
          assert.isNull(err)
          db.insert({ planet: 'Mars' }, function (err) {
            assert.isNull(err)

            // eslint-disable-next-line node/handle-callback-err
            db.ensureIndex({ fieldName: 'planet', unique: true, sparse: false }, function (err) {
              Object.keys(db.indexes).length.should.equal(2)
              Object.keys(db.indexes)[0].should.equal('_id')
              Object.keys(db.indexes)[1].should.equal('planet')
              db.indexes._id.getAll().length.should.equal(2)
              db.indexes.planet.getAll().length.should.equal(2)
              db.indexes.planet.unique.should.equal(true)
              db.indexes.planet.sparse.should.equal(false)

              db.insert({ planet: 'Jupiter' }, function (err) {
                assert.isNull(err)

                // After a reload the indexes are recreated
                db = new Datastore({ filename: persDb })
                db.loadDatabase(function (err) {
                  assert.isNull(err)
                  Object.keys(db.indexes).length.should.equal(2)
                  Object.keys(db.indexes)[0].should.equal('_id')
                  Object.keys(db.indexes)[1].should.equal('planet')
                  db.indexes._id.getAll().length.should.equal(3)
                  db.indexes.planet.getAll().length.should.equal(3)
                  db.indexes.planet.unique.should.equal(true)
                  db.indexes.planet.sparse.should.equal(false)

                  db.ensureIndex({ fieldName: 'bloup', unique: false, sparse: true }, function (err) {
                    assert.isNull(err)
                    Object.keys(db.indexes).length.should.equal(3)
                    Object.keys(db.indexes)[0].should.equal('_id')
                    Object.keys(db.indexes)[1].should.equal('planet')
                    Object.keys(db.indexes)[2].should.equal('bloup')
                    db.indexes._id.getAll().length.should.equal(3)
                    db.indexes.planet.getAll().length.should.equal(3)
                    db.indexes.bloup.getAll().length.should.equal(0)
                    db.indexes.planet.unique.should.equal(true)
                    db.indexes.planet.sparse.should.equal(false)
                    db.indexes.bloup.unique.should.equal(false)
                    db.indexes.bloup.sparse.should.equal(true)

                    // After another reload the indexes are still there (i.e. they are preserved during autocompaction)
                    db = new Datastore({ filename: persDb })
                    db.loadDatabase(function (err) {
                      assert.isNull(err)
                      Object.keys(db.indexes).length.should.equal(3)
                      Object.keys(db.indexes)[0].should.equal('_id')
                      Object.keys(db.indexes)[1].should.equal('planet')
                      Object.keys(db.indexes)[2].should.equal('bloup')
                      db.indexes._id.getAll().length.should.equal(3)
                      db.indexes.planet.getAll().length.should.equal(3)
                      db.indexes.bloup.getAll().length.should.equal(0)
                      db.indexes.planet.unique.should.equal(true)
                      db.indexes.planet.sparse.should.equal(false)
                      db.indexes.bloup.unique.should.equal(false)
                      db.indexes.bloup.sparse.should.equal(true)

                      done()
                    })
                  })
                })
              })
            })
          })
        })
      })

      it('Indexes can also be removed and the remove persisted', function (done) {
        const persDb = 'workspace/persistIndexes.db'
        let db

        if (fs.existsSync(persDb)) { fs.writeFileSync(persDb, '', 'utf8') }
        db = new Datastore({ filename: persDb, autoload: true })

        Object.keys(db.indexes).length.should.equal(1)
        Object.keys(db.indexes)[0].should.equal('_id')

        db.insert({ planet: 'Earth' }, function (err) {
          assert.isNull(err)
          db.insert({ planet: 'Mars' }, function (err) {
            assert.isNull(err)

            db.ensureIndex({ fieldName: 'planet' }, function (err) {
              assert.isNull(err)
              db.ensureIndex({ fieldName: 'another' }, function (err) {
                assert.isNull(err)
                Object.keys(db.indexes).length.should.equal(3)
                Object.keys(db.indexes)[0].should.equal('_id')
                Object.keys(db.indexes)[1].should.equal('planet')
                Object.keys(db.indexes)[2].should.equal('another')
                db.indexes._id.getAll().length.should.equal(2)
                db.indexes.planet.getAll().length.should.equal(2)
                db.indexes.planet.fieldName.should.equal('planet')

                // After a reload the indexes are recreated
                db = new Datastore({ filename: persDb })
                db.loadDatabase(function (err) {
                  assert.isNull(err)
                  Object.keys(db.indexes).length.should.equal(3)
                  Object.keys(db.indexes)[0].should.equal('_id')
                  Object.keys(db.indexes)[1].should.equal('planet')
                  Object.keys(db.indexes)[2].should.equal('another')
                  db.indexes._id.getAll().length.should.equal(2)
                  db.indexes.planet.getAll().length.should.equal(2)
                  db.indexes.planet.fieldName.should.equal('planet')

                  // Index is removed
                  db.removeIndex('planet', function (err) {
                    assert.isNull(err)
                    Object.keys(db.indexes).length.should.equal(2)
                    Object.keys(db.indexes)[0].should.equal('_id')
                    Object.keys(db.indexes)[1].should.equal('another')
                    db.indexes._id.getAll().length.should.equal(2)

                    // After a reload indexes are preserved
                    db = new Datastore({ filename: persDb })
                    db.loadDatabase(function (err) {
                      assert.isNull(err)
                      Object.keys(db.indexes).length.should.equal(2)
                      Object.keys(db.indexes)[0].should.equal('_id')
                      Object.keys(db.indexes)[1].should.equal('another')
                      db.indexes._id.getAll().length.should.equal(2)

                      // After another reload the indexes are still there (i.e. they are preserved during autocompaction)
                      db = new Datastore({ filename: persDb })
                      db.loadDatabase(function (err) {
                        assert.isNull(err)
                        Object.keys(db.indexes).length.should.equal(2)
                        Object.keys(db.indexes)[0].should.equal('_id')
                        Object.keys(db.indexes)[1].should.equal('another')
                        db.indexes._id.getAll().length.should.equal(2)

                        done()
                      })
                    })
                  })
                })
              })
            })
          })
        })
      })
    }) // ==== End of 'Persisting indexes' ====

    it('Results of getMatching should never contain duplicates', function (done) {
      d.ensureIndex({ fieldName: 'bad' })
      d.insert({ bad: ['a', 'b'] }, function () {
        // eslint-disable-next-line node/handle-callback-err
        callbackify(query => d._getCandidatesAsync(query))({ bad: { $in: ['a', 'b'] } }, function (err, res) {
          res.length.should.equal(1)
          done()
        })
      })
    })
  }) // ==== End of 'Using indexes' ==== //
})