Update Changelog in README.md when dependencies are updated in package.json

changelog-add-dependencies.js

#!/usr/bin/env node

/**
 * In private projects I usually keep changelog in README.md.
 *
 * It looks like:
 *
 *   ## Changelog
 *
 *   ### Version
 *
 *   DESCRIPTION
 *
 *   * feature1
 *   * feature2
 *   * Updated dependencies:
 *       * Updated `async` to `1.4.2`
 *       * Added `redis@1.0.0`
 *       * Removed `socket.io`
 *
 * The idea is dependency updates are reflected
 * in changelog too in the end of each version
 * description.
 *
 * This script assumes only dependencies
 * are changed in package.json file and are
 * not committed yet.
 *
 * What it does:
 *   - Updates changelog record for given version
 *     with dependencies update info
 *   - Commits package.json using Angular commit style:
 *     chore(npm): update dependencies
 *   - Updates package.json with new version (does not
 *     commit though)
 *
 * Run:
 *   changelog-add-dependencies.js [major|minor|patch|d.d.d-s]
 */

var execSync = require('child_process').execSync;
var fs = require('fs');
var path = require('path');
var util = require('util');

var PACKAGE_JSON_PATH = path.resolve(process.cwd(), 'package.json');
var PACKAGE_JSON = JSON.parse(fs.readFileSync(PACKAGE_JSON_PATH).toString('utf8'));
var VERSION = detectVersion(process.argv[2] || 'patch'); 

var CHANGELOG_LINE = '## Changelog\n';
var VERSION_LINE = '### ' + VERSION + '\n';

var stdout = execSync('git diff package.json | grep -E \'^[-+] \'').toString('utf8').split('\n').filter(Boolean);
var mapped = stdout.map(extract).reduce(group, []);
var markdown = mapped.filter(equalVersion).sort(byPackage).map(toMarkdown);
markdown.unshift('* Updated dependencies:');
markdown.push('');
insertInfo(markdown);

function extract(line) {
  var match = line.match(/^([-+])\s+"([^"]+)": "\^([^"]+)",?$/);
  return {
    isNew: match[1] === '+',
    packageName: match[2],
    version: match[3]
  };
}

function group(out, dep) {
  var rec;
  if (!(rec = getByPackage(out, dep.packageName))) {
    rec = {
      packageName: dep.packageName
    };
    out.push(rec);
  }
  if (dep.isNew) {
    rec.new = dep.version;
  }
  else {
    rec.old = dep.version;
  }
  return out;
}

function equalVersion(rec) {
  return rec.new !== rec.old;
}

function getByPackage(arr, packageName) {
  var i = 0;
  var rec;
  while ((rec = arr[i++])) {
    if (rec.packageName === packageName) {
      return rec;
    }
  }
}

function byPackage(a, b) {
  if (a.packageName < b.packageName) {
	  return -1;
	}
	else if (a.packageName === b.packageName) {
		return 0;
	}
	return 1;
}

function toMarkdown(rec) {
  var out = [];
  if (rec.new && rec.old) {
    out.push(util.format('    * Updated `%s` to `%s`', rec.packageName, rec.new));
  }
  else if (rec.new) {
    out.push(util.format('    * Added `%s@%s`', rec.packageName, rec.new));
  }
  else if (rec.old) {
    out.push(util.format('    * Removed `%s`', rec.packageName));
  }
  return out.join('\n');
}

function getIndex(str) {
  return function reduce(out, line, idx) {
    if (line.indexOf(str) === 0) {
      return idx;
    }
    else {
      return out;
    }
  };
}

function insertInfo(lines) {
  var readme = fs.readFileSync('./README.md').toString('utf8');
  var sections = readme.split(/\n## /);
  var changelogIdx = sections.reduce(getIndex('Changelog'), -1);
  var changelog;
  var versions;
  var versionIdx = -1;
  var version;
  var depIdx = -1;
  if (~changelogIdx) {
    changelog = sections[changelogIdx];
    versions = changelog.split('### ');
    versionIdx = versions.reduce(getIndex(VERSION), -1);
  }
  if (~versionIdx) {
    version = versions[versionIdx];
    depIdx = version.indexOf('* Updated dependencies:');
  }
  if (~depIdx) {
    version = version.substring(0, depIdx);
  }
  if (~versionIdx) {
    versions[versionIdx] = version.replace(/\n*$/, '\n') + lines.join('\n') + '\n';
    sections[changelogIdx] = versions.join('### ');
    readme = sections.join('\n## ');
  }
  else if (~changelogIdx) {
    lines.unshift(VERSION_LINE);
    var parts = changelog.split('\n');
    parts.splice(2, 0, lines.join('\n'));
    sections[changelogIdx] = parts.join('\n');
    readme = sections.join('\n## ');
  }
  else {
    lines.unshift(CHANGELOG_LINE, VERSION_LINE);
    readme = sections.join('\n## ').replace(/\n$/, '') + '\n\n' + lines.join('\n');
  }
  fs.unlinkSync('./README.md');
  fs.writeFileSync('./README.md', readme);
  execSync('git reset ./*');
  execSync('git add package.json');
  execSync('git commit -m "chore(npm): update dependencies"');
  PACKAGE_JSON.version = VERSION;
  fs.writeFileSync(PACKAGE_JSON_PATH, JSON.stringify(PACKAGE_JSON, null, '  ') + '\n');
}

function detectVersion(version) {
  if (/^\d+\.\d+\.\d+$/.test(version)) {
    return version;
  }

  var idx = ['major', 'minor', 'patch'].indexOf(version);
  if (!~idx) {
    throw new Error('Wrong version identifier: ' + version);
  }

	var vvv = PACKAGE_JSON.version.replace(/-.*$/g, '').split('.').map(toInt);
  function toInt(str) {
    return parseInt(str, 10);
  }

  vvv[idx]++;
	while (++idx < 3) {
    vvv[idx] = 0;
	}
  return vvv.join('.');
}