Determine whether to run patternlab build based on changed files in a compilation

compilation-files-changed-plugin.js

import patternEngines from 'patternlab-node/core/lib/pattern_engines';
import plConfig from '../../../patternlab-config.json';

const pluginName = 'CompilationFilesChangedPlugin';

class CompilationFilesChangedPlugin {
  constructor({ patternlab }) {
    this.startTime = Date.now();
    this.prevTimestamps = new Map();
    this.pluginIterator = 0;
    this.supportedTemplateExtensions = patternEngines.getSupportedFileExtensions();
    // the following method does not exist - how to get this list from PL?
    this.supportedDataExtensions = plConfig.supportedDataExtensions || [];
    this.cleanPublic = plConfig.cleanPublic || false;
    process.argv.forEach((val, index) => {
      if (val.includes('cleanPublic')) {
        val = val.split('=');
        this.cleanPublic = JSON.parse(val[1]);
      }
    });
    this.plCore = patternlab;
    this.checkBuildNecessary = this.checkBuildNecessary.bind(this);
  }

  apply(compiler) {
    if (compiler.hooks) {
      compiler.hooks.afterEmit.tapAsync(pluginName, this.checkBuildNecessary);
    } else {
      compiler.plugin('after-emit', this.checkBuildNecessary);
    }
  }

  checkBuildNecessary(compilation, callback = () => {}) {
    let buildPatterns = false;
    let changedPatternFilesArr = [];
    const hasPrevTimestamps = this.prevTimestamps.size > 0;
    // remove leading dot from each filetype extension before creating regex,
    // then concat the data (or content) types from a hard-coded string array
    const patternFileTypes = this.supportedTemplateExtensions
      .map(ext => ext.slice(1))
      .concat(this.supportedDataExtensions)
      .join('|');
    const patternFiletypeTextRegex = new RegExp(`.*\\.(${patternFileTypes})$`);
    const changedFileKeys = [...compilation.fileTimestamps.keys()];
    const changedFiles = changedFileKeys.filter(
      function(watchfile) {
        if (typeof this === 'undefined' || !hasPrevTimestamps) {
          return false;
        }
        return (
          (this.prevTimestamps.get(watchfile) || this.startTime) <
          (compilation.fileTimestamps.get(watchfile) || Infinity)
        );
      }.bind(this)
    );

    changedPatternFilesArr =
      (this.supportedTemplateExtensions.length > 0 || this.supportedDataExtensions.length > 0)
        ? changedFiles.filter(filePath =>
            patternFiletypeTextRegex.test(filePath)
          )
        : changedFiles;

    // Assumption: Build only when timestamps show that a pattern file (template file) has changed
    // First iteration always assumes that patterns need to be built:

    buildPatterns =
      this.pluginIterator === 0 || changedPatternFilesArr.length > 0;

    this.prevTimestamps = compilation.fileTimestamps; // update the timestamps for next iteration
    this.pluginIterator++;

    buildPatterns ? this.plCore.build(callback, this.cleanPublic) : callback();
  }
}

export default CompilationFilesChangedPlugin;