From 176d53c4ee220beca360ac4c6f46428068c59e39 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timoth=C3=A9e=20Rebours?= <tim@seald.io>
Date: Thu, 21 Oct 2021 15:48:07 +0200
Subject: [PATCH] WIP: rewrite executor without async

---
 lib/datastore.js    | 31 ++++++++++------
 lib/executor.js     | 87 +++++++++++++++++++++++++++++++++------------
 test/cursor.test.js | 10 +++---
 3 files changed, 89 insertions(+), 39 deletions(-)

diff --git a/lib/datastore.js b/lib/datastore.js
index 57dccc6..8d45b89 100755
--- a/lib/datastore.js
+++ b/lib/datastore.js
@@ -89,6 +89,15 @@ class Datastore extends EventEmitter {
     this.executor.push({ this: this.persistence, fn: this.persistence.loadDatabase, arguments: arguments }, true)
   }
 
+  loadDatabaseAsync () {
+    return this.executor.push({
+      this: this.persistence,
+      fn: this.persistence.loadDatabaseAsync,
+      arguments: arguments,
+      async: true
+    }, true)
+  }
+
   /**
    * Get an array of all the data in the database
    */
@@ -343,19 +352,15 @@ class Datastore extends EventEmitter {
    * @private
    */
   _insert (newDoc, callback = () => {}) {
-    let preparedDoc
+    return callbackify(this._insertAsync.bind(this))(newDoc, callback)
+  }
 
-    try {
-      preparedDoc = this._prepareDocumentForInsertion(newDoc)
-      this._insertInCache(preparedDoc)
-    } catch (e) {
-      return callback(e)
-    }
+  async _insertAsync (newDoc) {
+    const preparedDoc = this._prepareDocumentForInsertion(newDoc)
+    this._insertInCache(preparedDoc)
 
-    this.persistence.persistNewState(Array.isArray(preparedDoc) ? preparedDoc : [preparedDoc], err => {
-      if (err) return callback(err)
-      return callback(null, model.deepCopy(preparedDoc))
-    })
+    await this.persistence.persistNewStateAsync(Array.isArray(preparedDoc) ? preparedDoc : [preparedDoc])
+    return model.deepCopy(preparedDoc)
   }
 
   /**
@@ -433,6 +438,10 @@ class Datastore extends EventEmitter {
     this.executor.push({ this: this, fn: this._insert, arguments: arguments })
   }
 
+  insertAsync () {
+    this.executor.push({ this: this, fn: this._insertAsync, arguments: arguments, async: true })
+  }
+
   /**
    * Count all documents matching the query
    * @param {Query} query MongoDB-style query
diff --git a/lib/executor.js b/lib/executor.js
index 98a9c4c..dd866ec 100755
--- a/lib/executor.js
+++ b/lib/executor.js
@@ -1,41 +1,84 @@
 /**
  * Responsible for sequentially executing actions on the database
  */
-const async = require('async')
+
+const makeQueue = execute => {
+  const tasks = new Map()
+  let running = false
+  let drainPromise = Promise.resolve()
+  const executeNextTask = async (self = false) => {
+    if (!tasks.size) {
+      running = false
+      return
+    } else if (running && !self) {
+      return
+    }
+    running = true
+    const [task, { resolve, reject }] = tasks[Symbol.iterator]().next().value
+
+    tasks.delete(task)
+    try {
+      resolve(await execute(task))
+    } catch (err) {
+      reject(err)
+    }
+    drainPromise = executeNextTask(true)
+  }
+
+  return {
+    push (task) {
+      let _resolve, _reject
+      const promise = new Promise((resolve, reject) => {
+        _reject = reject
+        _resolve = resolve
+      })
+      tasks.set(task, { resolve: _resolve, reject: _reject })
+      if (!running) drainPromise = executeNextTask()
+      return promise
+    },
+    async drain () {
+      return drainPromise
+    }
+  }
+}
 
 class Executor {
   constructor () {
     this.buffer = []
     this.ready = false
 
-    // This queue will execute all commands, one-by-one in order
-    this.queue = async.queue((task, cb) => {
+    this.queue = makeQueue(async task => {
       // task.arguments is an array-like object on which adding a new field doesn't work, so we transform it into a real array
       const newArguments = Array.from(task.arguments)
 
-      const lastArg = newArguments[newArguments.length - 1]
-
-      // Always tell the queue task is complete. Execute callback if any was given.
-      if (typeof lastArg === 'function') {
-        // Callback was supplied
-        newArguments[newArguments.length - 1] = function () {
-          if (typeof setImmediate === 'function') {
-            setImmediate(cb)
+      // If the task isn't async, let's proceed with the old handler
+      if (!task.async) {
+        const lastArg = newArguments[newArguments.length - 1]
+        await new Promise(resolve => {
+          if (typeof lastArg === 'function') {
+            // We got a callback
+            newArguments.pop() // remove original callback
+            task.fn.apply(task.this, [...newArguments, function () {
+              resolve() // triggers next task after next tick
+              lastArg.apply(null, arguments) // call original callback
+            }])
+          } else if (!lastArg && task.arguments.length !== 0) {
+            // We got a falsy callback
+            newArguments.pop() // remove original callback
+            task.fn.apply(task.this, [...newArguments, () => {
+              resolve()
+            }])
           } else {
-            process.nextTick(cb)
+            // We don't have a callback
+            task.fn.apply(task.this, [...newArguments, () => {
+              resolve()
+            }])
           }
-          lastArg.apply(null, arguments)
-        }
-      } else if (!lastArg && task.arguments.length !== 0) {
-        // false/undefined/null supplied as callback
-        newArguments[newArguments.length - 1] = () => { cb() }
+        })
       } else {
-        // Nothing supplied as callback
-        newArguments.push(() => { cb() })
+        await task.fn.apply(task.this, newArguments)
       }
-
-      task.fn.apply(task.this, newArguments)
-    }, 1)
+    })
   }
 
   /**
diff --git a/test/cursor.test.js b/test/cursor.test.js
index f1fe16d..42d8566 100755
--- a/test/cursor.test.js
+++ b/test/cursor.test.js
@@ -29,12 +29,10 @@ describe('Cursor', function () {
           })
         })
       },
-      function (cb) {
-        d.loadDatabase(function (err) {
-          assert.isNull(err)
-          d.getAllData().length.should.equal(0)
-          return cb()
-        })
+      async function (cb) {
+        await d.loadDatabaseAsync()
+        d.getAllData().length.should.equal(0)
+        cb()
       }
     ], done)
   })