Resolves #362: replace generator functions with promises

lib/helpers.js

@@ -1,6 +1,6 @@
 const fs = require('fs')
 const { promisify } = require('util')
-const { resolve, relative, normalize } = require('path')
+const { resolve, relative, normalize, dirname } = require('path')
 const rmrf = require('rimraf')
 const micromatch = require('micromatch')
 
@@ -67,11 +67,11 @@ function rm(p) {
 
 /**
  * Recursive readdir with support for ignores
+ * @private
  * @param {String} dir
  * @param {Array<String|Function>} ignores
- * @param {Function} callback - Callback for thunkify @TODO remove in the future
  */
-function readdir(dir, ignores, callback) {
+function readdir(dir, ignores) {
   if (Array.isArray(ignores)) {
     ignores = {
       str: ignores.filter(isString),
@@ -122,15 +122,47 @@ function readdir(dir, ignores, callback) {
         .sort()
       return result
     })
+    .catch((err) => {
+      throw err
+    })
+
+  return result
+}
+
+/**
+ * Run `fn` in parallel on #`concurrency` number of `items`, spread over #`items / concurrency` sequential batches
+ * @private
+ * @param {() => Promise} fn
+ * @param {*[]} items
+ * @param {number} concurrency
+ * @returns {Promise<*[]>}
+ */
+function batchAsync(fn, items, concurrency) {
+  let batches = Promise.resolve([])
+  items = [...items]
 
-  if (callback) {
-    result.then(
-      (files) => callback(null, files),
-      (err) => callback(err)
-    )
-  } else {
-    return result
+  while (items.length) {
+    const slice = items.splice(0, concurrency)
+    batches = batches.then((previousBatch) => {
+      return Promise.all(slice.map((...args) => fn(...args))).then((currentBatch) => [
+        ...previousBatch,
+        ...currentBatch
+      ])
+    })
   }
+
+  return batches
+}
+
+/**
+ * Output a file and create any non-existing directories in the process
+ * @private
+ **/
+function outputFile(file, data, mode) {
+  const writeFile = promisify(fs.writeFile)
+  return promisify(fs.mkdir)(dirname(file), { recursive: true }).then(() => {
+    return writeFile(file, data, mode ? { mode } : undefined)
+  })
 }
 
 const helpers = {
@@ -139,9 +171,12 @@ const helpers = {
   isString,
   isObject,
   isUndefined,
+  isFunction,
   match,
   rm,
-  readdir
+  readdir,
+  outputFile,
+  batchAsync
 }
 
 module.exports = helpers