Added changelog generation to build in gruntfile

Fixes #291

Incorporated new task into gruntfile which generates a markdown formatted
changelog from the git commit messages of the last 14 git tags, corresponding
to two weeks of nightly releases.

The changelog is saved in __dirname/CHANGELOG.md.

At this stage, the code is a fair bit too complex to be left in the gruntfile
and should be split out into a separate module, but this is a first bash at the
function which can be improved later.

Additionally, several additions have been made to the generator to improve
reliability:

- Now generates changelog based on log output with --graph (thx hannah)
- Grabs tag refs from git
- Added changelog to gitignore
- Added message for builds without any changes
- Ignores any commits which have not been incorporated into a build

.gitignore

@@ -37,3 +37,6 @@ projectFilesBackup
 /core/server/data/export/exported*
 /docs
 /_site
+
+# Changelog, which is autogenerated, not committed
+CHANGELOG.md

Gruntfile.js

@@ -1,4 +1,9 @@
 var path = require('path'),
+    when = require('when'),
+    semver = require("semver"),
+    fs = require("fs"),
+    path = require("path"),
+    spawn = require("child_process").spawn,
     buildDirectory = path.resolve(process.cwd(), '.build'),
     distDirectory =  path.resolve(process.cwd(), '.dist'),
     configureGrunt = function (grunt) {
@@ -34,7 +39,9 @@ var path = require('path'),
                         // allow unused parameters
                         unparam: true,
                         // don't require use strict pragma
-                        sloppy: true
+                        sloppy: true,
+                        // allow bitwise operators
+                        bitwise: true
                     },
                     files: {
                         src: [
@@ -300,9 +307,253 @@ var path = require('path'),
         // Generate Docs
         grunt.registerTask("docs", ["groc"]);
 
+        /* Generate Changelog
+         * - Pulls changelog from git, excluding merges.
+         * - Uses first line of commit message. Includes committer name.
+         */
+        grunt.registerTask("changelog", "Generate changelog from Git", function () {
+            // TODO: Break the contents of this task out into a separate module,
+            // put on npm. (@cgiffard)
+
+            var done = this.async();
+
+            function git(args, callback, depth) {
+                depth = depth || 0;
+
+                if (!depth) {
+                    grunt.log.writeln("git " + args.join(" "));
+                }
+
+                var buffer = [];
+                spawn("git", args, {
+                    // We can reasonably assume the gruntfile will be in the root of the repo.
+                    cwd : __dirname,
+
+                    stdio : ["ignore", "pipe", process.stderr]
+
+                }).on("exit", function (code) {
+
+                    // Process exited correctly but we got no output.
+                    // Spawn again, but make sure we don't spiral out of control.
+                    // Hack to work around an apparent node bug.
+                    //
+                    // Frustratingly, it's impossible to distinguish this
+                    // bug from a genuine empty log.
+
+                    if (!buffer.length && code === 0 && depth < 20) {
+                        return setImmediate(function () {
+                            git(args, callback, depth ? depth + 1 : 1);
+                        });
+                    }
+
+                    if (code === 0) {
+                        return callback(buffer.join(""));
+                    }
+
+                    // We failed. Git returned a non-standard exit code.
+                    grunt.log.error('Git returned a non-zero exit code.');
+                    done(false);
+
+                // Push returned data into the buffer
+                }).stdout.on("data", buffer.push.bind(buffer));
+            }
+
+            // Crazy function for getting around inconsistencies in tagging
+            function sortTags(a, b) {
+                a = a.tag;
+                b = b.tag;
+
+                // NOTE: Accounting for different tagging method for
+                // 0.2.1 and up.
+
+                // If we didn't have this issue I'd just pass rcompare
+                // into sort directly. Could be something to think about
+                // in future.
+
+                if (semver.rcompare(a, "0.2.0") < 0 ||
+                        semver.rcompare(b, "0.2.0") < 0) {
+
+                    return semver.rcompare(a, b);
+                }
+
+                a = a.split("-");
+                b = b.split("-");
+
+                if (semver.rcompare(a[0], b[0]) !== 0) {
+                    return semver.rcompare(a[0], b[0]);
+                }
+
+                // Using this janky looking integerising-method
+                // because it's faster and doesn't result in NaN, which
+                // breaks sorting
+                return (+b[1] | 0) - (+a[1] | 0);
+            }
+
+            // Gets tags in master branch, sorts them with semver,
+            function getTags(callback) {
+                git(["show-ref", "--tags"], function (results) {
+                    results = results
+                        .split(/\n+/)
+                        .filter(function (tag) {
+                            return tag.length && tag.match(/\/\d+\.\d+/);
+                        })
+                        .map(function (tag) {
+                            return {
+                                "tag": tag.split(/tags\//).pop().trim(),
+                                "ref": tag.split(/\s+/).shift().trim(),
+                            };
+                        })
+                        .sort(sortTags);
+
+                    callback(results);
+                });
+            }
+
+            // Parses log to extract commit data.
+            function parseLog(data) {
+                var commits = [],
+                    commitRegex =
+                        new RegExp(
+                            "\\n*[|\\*\\s]*commit\\s+([a-f0-9]+)" +
+                                "\\n[|\\*\\s]*Author:\\s+([^<\\n]+)<([^>\\n]+)>" +
+                                "\\n[|\\*\\s]*Date:\\s+([^\\n]+)" +
+                                "\\n+[|\\*\\s]*[ ]{4}([^\\n]+)",
+                            "ig"
+                        );
+
+                // Using String.prototype.replace as a kind of poor-man's substitute
+                // for a streaming parser.
+                data.replace(
+                    commitRegex,
+                    function (wholeCommit, hash, author, email, date, message) {
+
+                        // The author name and commit message may have trailing space.
+                        author = author.trim();
+                        message = message.trim();
+
+                        // Reformat date to make it parse-able by JS
+                        date =
+                            date.replace(
+                                /^(\w+)\s(\w+)\s(\d+)\s([\d\:]+)\s(\d+)\s([\+\-\d]+)$/,
+                                "$1, $2 $3 $5 $4 $6"
+                            );
+
+                        commits.push({
+                            "hash": hash,
+                            "author": author,
+                            "email": email,
+                            "date": date,
+                            "parsedDate": new Date(Date.parse(date)),
+                            "message": message
+                        });
+
+                        return null;
+                    }
+                );
+
+                return commits;
+            }
+
+            // Gets git log for specified range.
+            function getLog(to, from, callback) {
+                var range = from && to ? from + ".." + to : "",
+                    args = [ "log", "master", "--no-color", "--no-merges", "--graph" ];
+
+                if (range) {
+                    args.push(range);
+                }
+
+                git(args, function (data) {
+                    callback(parseLog(data));
+                });
+            }
+
+            // Run the job
+            getTags(function (tags) {
+                var logPath = path.join(__dirname, "CHANGELOG.md"),
+                    log = fs.createWriteStream(logPath),
+                    commitCache = {};
+
+                function processTag(tag, callback) {
+                    var buffer = "",
+                        peek = tag[1];
+
+                    tag = tag[0];
+
+                    getLog(tag.tag, peek.tag, function (commits) {
+
+                        // Use the comparison with HEAD to remove commits which
+                        // haven't been included in a build/release yet.
+
+                        if (tag.tag === "HEAD") {
+                            commits.forEach(function (commit) {
+                                commitCache[commit.hash] = true;
+                            });
+
+                            return callback("");
+                        }
+
+                        buffer += "## Release " + tag.tag + "\n";
+
+                        commits = commits
+                            .filter(function (commit) {
+
+                                // Get rid of jenkins' release tagging commits
+                                // Remove commits we've already spat out
+                                return (
+                                    commit.author !== "TryGhost-Jenkins" &&
+                                    !commitCache[commit.hash]
+                                );
+                            })
+                            .map(function (commit) {
+                                buffer += "\n* " + commit.message + " (_" + commit.author + "_)";
+                                commitCache[commit.hash] = true;
+                            });
+
+                        if (!commits.length) {
+                            buffer += "\nNo changes were made in this build.\n";
+                        }
+
+                        callback(buffer + "\n");
+                    });
+                }
+
+                // Get two weeks' worth of tags
+                tags.unshift({"tag": "HEAD"});
+
+                tags =
+                    tags
+                        .slice(0, 14)
+                        .map(function (tag, index) {
+                        return [
+                            tag,
+                            tags[index + 1] || tags[index]
+                        ];
+                    });
+
+                log.write("# Ghost Changelog\n\n");
+                log.write("_Showing " + tags.length + " releases._\n");
+
+                when.reduce(tags,
+                    function (prev, tag, idx) {
+                        return when.promise(function (resolve) {
+                            processTag(tag, function (releaseData) {
+                                resolve(prev + "\n" + releaseData);
+                            });
+                        });
+                    }, "")
+                    .then(function (reducedChangelog) {
+                        log.write(reducedChangelog);
+                        log.close();
+                        done(true);
+                    });
+            });
+        });
+
         /* Nightly builds
          * - Do our standard build steps (sass, handlebars, etc)
          * - Bump patch version in package.json, commit, tag and push
+         * - Generate changelog for the past 14 releases
          * - Copy files to build-folder/#/#{version} directory
          * - Clean out unnecessary files (travis, .git*, .af*, .groc*)
          * - Zip files in build folder to dist-folder/#{version} directory
@@ -314,6 +565,7 @@ var path = require('path'),
             "handlebars",
             "bump:build",
             "updateCurrentPackageInfo",
+            "changelog",
             "copy:nightly",
             "compress:nightly"
         ]);
@@ -325,6 +577,7 @@ var path = require('path'),
             "handlebars",
             "bump:build",
             "updateCurrentPackageInfo",
+            "changelog",
             "copy:weekly",
             "compress:weekly"
         ]);
@@ -333,6 +586,7 @@ var path = require('path'),
             "shell:bourbon",
             "sass:admin",
             "handlebars",
+            "changelog",
             "copy:build",
             "compress:build"
         ]);