feat: add promise support (#18) (#19)

* return Promise if 'parseChangelog()' is invoked without a callback.

* stub out tests for Promise functonality/support.

* update 'parseChangelog()' so that concurrent invocations do not mutate the same global vars.

* update tests: ensure that 'callback' and 'Promise' approaches return same value.

* docs(readme): update 'Usage' section with Promise info.

* fix linting errors.

Author: jrmykolyn

README.md

@@ -23,12 +23,25 @@ npm install changelog-parser
 ```js
 var parseChangelog = require('changelog-parser')
 
+// CALLBACK
+// If provided with a callback, `parseChangelog` will invoke the function with the parsed changelog.
 parseChangelog('path/to/CHANGELOG.md', function (err, result) {
   if (err) throw err
 
   // changelog object
   console.log(result)
 })
+
+// Promise
+// If no callback is provided, `parseChangelog` will return a Promise.
+parseChangelog('path/to/CHANGELOG.md')
+    .then(function(result) {
+        // changelog object
+        console.log(result)
+    })
+    .catch(() {
+        // Whoops, something went wrong!
+    })
 ```
 
 ### Command-line interface

index.js

@@ -2,22 +2,39 @@ var EOL = require('os').EOL
 var lineReader = require('line-reader')
 var semver = /\[?v?([\w\d.-]+\.[\w\d.-]+[a-zA-Z0-9])\]?/
 var date = /.*([\d]{4}-[\d]{2}-[\d]{2}).*/
-var log
-var current
 
 function parseChangelog (file, callback) {
-  log = { versions: [] }
-  current = null
+  // return a Promise if invoked without a `callback`
+  if (!callback || typeof callback !== 'function') {
+    return doParse(file)
+  }
 
-  lineReader.eachLine(file, handleLine, EOL).then(function () {
-    // push last version into log
-    pushCurrent()
+  // otherwise, parse log and invoke callback
+  doParse(file).then(function (log) {
+    callback(null, log)
+  })
+}
 
-    // clean up description
-    log.description = clean(log.description)
-    if (log.description === '') delete log.description
+function doParse (file) {
+  var data = {
+    log: { versions: [] },
+    current: null
+  }
 
-    callback(null, log)
+  // allow `handleLine` to mutate log/current data as `this`.
+  var cb = handleLine.bind(data)
+
+  return new Promise(function (resolve, reject) {
+    lineReader.eachLine(file, cb, EOL).then(function () {
+      // push last version into log
+      pushCurrent(data)
+
+      // clean up description
+      data.log.description = clean(data.log.description)
+      if (data.log.description === '') delete data.log.description
+
+      resolve(data.log)
+    })
   })
 }
 
@@ -26,31 +43,31 @@ function handleLine (line) {
   if (line.match(/^\[[^[\]]*\] *?:/)) return
 
   // set title if it's there
-  if (!log.title && line.match(/^# ?[^#]/)) {
-    log.title = line.substring(1).trim()
+  if (!this.log.title && line.match(/^# ?[^#]/)) {
+    this.log.title = line.substring(1).trim()
     return
   }
 
   // new version found!
   if (line.match(/^## ?[^#]/)) {
-    if (current && current.title) pushCurrent()
+    if (this.current && this.current.title) pushCurrent(this)
 
-    current = versionFactory()
+    this.current = versionFactory()
 
-    if (semver.exec(line)) current.version = semver.exec(line)[1]
+    if (semver.exec(line)) this.current.version = semver.exec(line)[1]
 
-    current.title = line.substring(2).trim()
+    this.current.title = line.substring(2).trim()
 
-    if (current.title && date.exec(current.title)) current.date = date.exec(current.title)[1]
+    if (this.current.title && date.exec(this.current.title)) this.current.date = date.exec(this.current.title)[1]
 
     return
   }
 
   // deal with body or description content
-  if (current) {
-    current.body += line + EOL
+  if (this.current) {
+    this.current.body += line + EOL
   } else {
-    log.description = (log.description || '') + line + EOL
+    this.log.description = (this.log.description || '') + line + EOL
   }
 }
 
@@ -63,9 +80,9 @@ function versionFactory () {
   }
 }
 
-function pushCurrent () {
-  current.body = clean(current.body)
-  log.versions.push(current)
+function pushCurrent (data) {
+  data.current.body = clean(data.current.body)
+  data.log.versions.push(data.current)
 }
 
 function clean (str) {

test/index.js

@@ -48,3 +48,36 @@ test('meet expectations', function (t) {
     t.end()
   })
 })
+
+test('returns a Promise when invoked without a valid `callback`', function (t) {
+  t.plan(2)
+
+  var result = parseChangelog(path.join(__dirname, 'CHANGELOG.md'))
+
+  t.true(typeof result === 'object')
+  t.true(result instanceof Promise)
+})
+
+test('resolved Promise contains a "CHANGELOG" object', function (t) {
+  t.plan(1)
+
+  parseChangelog(path.join(__dirname, 'CHANGELOG.md')).then(function (result) {
+    t.deepEqual(result, expected)
+    t.end()
+  })
+})
+
+test('callback and Promise methods should yield identical values', function (t) {
+  t.plan(1)
+
+  parseChangelog(path.join(__dirname, 'CHANGELOG.md'), function (err, resultA) {
+    if (err) t.fail()
+
+    parseChangelog(path.join(__dirname, 'CHANGELOG.md'))
+            .then(function (resultB) {
+              t.deepEqual(resultA, resultB)
+              t.end()
+            })
+            .catch(t.fail)
+  })
+})