/* eslint-env mocha */
const chai = require('chai')
const testDb = 'workspace/test.db'
const fs = require('fs')
const { waterfall } = require('./utils.test.js')
const Datastore = require('../lib/datastore')
const Persistence = require('../lib/persistence')
const { callbackify } = require('util')

const { assert } = chai
chai.should()

// Test that even if a callback throws an exception, the next DB operations will still be executed
// We prevent Mocha from catching the exception we throw on purpose by remembering all current handlers, remove them and register them back after test ends
function testThrowInCallback (d, done) {
  const currentUncaughtExceptionHandlers = process.listeners('uncaughtException')
  const currentUnhandledRejectionHandlers = process.listeners('unhandledRejection')

  process.removeAllListeners('uncaughtException')
  process.removeAllListeners('unhandledRejection')

  // eslint-disable-next-line n/handle-callback-err
  process.on('uncaughtException', function (err) {
    // Do nothing with the error which is only there to test we stay on track
  })

  process.on('unhandledRejection', function MINE (ex) {
    // Do nothing with the error which is only there to test we stay on track
  })

  // eslint-disable-next-line n/handle-callback-err
  d.find({}, function (err) {
    process.nextTick(function () {
      // eslint-disable-next-line n/handle-callback-err
      d.insert({ bar: 1 }, function (err) {
        process.removeAllListeners('uncaughtException')
        process.removeAllListeners('unhandledRejection')
        for (let i = 0; i < currentUncaughtExceptionHandlers.length; i += 1) {
          process.on('uncaughtException', currentUncaughtExceptionHandlers[i])
        }
        for (let i = 0; i < currentUnhandledRejectionHandlers.length; i += 1) {
          process.on('unhandledRejection', currentUnhandledRejectionHandlers[i])
        }

        done()
      })
    })

    throw new Error('Some error')
  })
}

// Test that if the callback is falsy, the next DB operations will still be executed
function testFalsyCallback (d, done) {
  d.insert({ a: 1 }, null)
  process.nextTick(function () {
    d.update({ a: 1 }, { a: 2 }, {}, null)
    process.nextTick(function () {
      d.update({ a: 2 }, { a: 1 }, null)
      process.nextTick(function () {
        d.remove({ a: 2 }, {}, null)
        process.nextTick(function () {
          d.remove({ a: 2 }, null)
          process.nextTick(function () {
            d.find({}, done)
          })
        })
      })
    })
  })
}

// Test that operations are executed in the right order
// We prevent Mocha from catching the exception we throw on purpose by remembering all current handlers, remove them and register them back after test ends
function testRightOrder (d, done) {
  const currentUncaughtExceptionHandlers = process.listeners('uncaughtException')

  process.removeAllListeners('uncaughtException')

  // eslint-disable-next-line n/handle-callback-err
  process.on('uncaughtException', function (err) {
    // Do nothing with the error which is only there to test we stay on track
  })

  // eslint-disable-next-line n/handle-callback-err
  d.find({}, function (err, docs) {
    docs.length.should.equal(0)

    d.insert({ a: 1 }, function () {
      d.update({ a: 1 }, { a: 2 }, {}, function () {
        // eslint-disable-next-line n/handle-callback-err
        d.find({}, function (err, docs) {
          docs[0].a.should.equal(2)

          process.nextTick(function () {
            d.update({ a: 2 }, { a: 3 }, {}, function () {
              // eslint-disable-next-line n/handle-callback-err
              d.find({}, function (err, docs) {
                docs[0].a.should.equal(3)

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

                done()
              })
            })
          })

          throw new Error('Some error')
        })
      })
    })
  })
}

// Note:  The following test does not have any assertion because it
// is meant to address the deprecation warning:
// (node) warning: Recursive process.nextTick detected. This will break in the next version of node. Please use setImmediate for recursive deferral.
// see
const testEventLoopStarvation = function (d, done) {
  const times = 1001
  let i = 0
  while (i < times) {
    i++
    // eslint-disable-next-line n/handle-callback-err
    d.find({ bogus: 'search' }, function (err, docs) {
    })
  }
  done()
}

// Test that operations are executed in the right order even with no callback
function testExecutorWorksWithoutCallback (d, done) {
  d.insert({ a: 1 })
  d.insert({ a: 2 }, false)
  // eslint-disable-next-line n/handle-callback-err
  d.find({}, function (err, docs) {
    docs.length.should.equal(2)
    done()
  })
}

describe('Executor', function () {
  describe('With persistent 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((filename) => Persistence.ensureParentDirectoryExistsAsync(filename))(testDb, function () {
            fs.access(testDb, fs.constants.F_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('A throw in a callback doesnt prevent execution of next operations', function (done) {
      testThrowInCallback(d, done)
    })

    it('A falsy callback doesnt prevent execution of next operations', function (done) {
      testFalsyCallback(d, done)
    })

    it('Operations are executed in the right order', function (done) {
      testRightOrder(d, done)
    })

    it('Does not starve event loop and raise warning when more than 1000 callbacks are in queue', function (done) {
      testEventLoopStarvation(d, done)
    })

    it('Works in the right order even with no supplied callback', function (done) {
      testExecutorWorksWithoutCallback(d, done)
    })
  }) // ==== End of 'With persistent database' ====

  describe('With non persistent database', function () {
    let d

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

      d.loadDatabase(function (err) {
        assert.isNull(err)
        d.getAllData().length.should.equal(0)
        return done()
      })
    })

    it('A throw in a callback doesnt prevent execution of next operations', function (done) {
      testThrowInCallback(d, done)
    })

    it('A falsy callback doesnt prevent execution of next operations', function (done) {
      testFalsyCallback(d, done)
    })

    it('Operations are executed in the right order', function (done) {
      testRightOrder(d, done)
    })

    it('Works in the right order even with no supplied callback', function (done) {
      testExecutorWorksWithoutCallback(d, done)
    })
  }) // ==== End of 'With non persistent database' ====
})