productionline/Monitor.js

An extendable class for creating common build pipelines.

const EventEmitter = require('events').EventEmitter
const path = require('path')

/**
 * Watch the source directory for changes. Any time a change occurs,
 * the callback is executed. Running this will prevent the build from
 * exiting, so it should only be used for development automation.
 * @param  {Function} callback
 * The method to execute when a file change is detected.
 * @param {String} callback.action
 * The type of action detected. This will be `create`, `update`, or `delete`.
 * @param {String} callback.path
 * The absolute path of the file or directory that changed.
 * @return {Object}
 * Returns the monitoring object (chokidar). This has a `close()` method to
 * stop watching.
 */
class Monitor extends EventEmitter {
  constructor (builder, callback) {
    super()

    Object.defineProperties(this, {
      callback: {
        enumerable: false,
        configurable: false,
        writable: false,
        value: callback
      },

      BUILDER: {
        enumerable: false,
        configurable: false,
        writable: false,
        value: builder
      },

      WATCHER: {
        enumerable: false,
        configurable: false,
        writable: true,
        value: null
      }
    })

    let chokidar = require('chokidar')

    this.WATCHER = chokidar.watch(path.join(this.BUILDER.SOURCE, path.sep), {
      ignored: this.BUILDER.IGNOREDLIST,
      ignoreInitial: true,
      persistent: true
    }).on('add', filepath => this.reset('create', filepath))
      .on('change', filepath => this.reset('update', filepath))
      .on('unlink', filepath => this.reset('delete', filepath))
      .on('error', error => console.error(error))
      .on('ready', () => this.emit('ready', this.WATCHER))
  }

  stop () {
    this.WATCHER.close()
    this.emit('close')
  }

  reset () {
    this.BUILDER.tasks.steps = []

    try {
      this.callback && this.callback(...arguments)
    } catch (e) {
      this.emit('error', e)
    }
  }
}

module.exports = Monitor