/**
 * Copyright 2020 Google LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
const URL = require('url');
const VM = require('vm');
const threads = require('worker_threads');
const WORKER = Symbol.for('worker');
const EVENTS = Symbol.for('events');
class EventTarget {
  constructor() {
    Object.defineProperty(this, EVENTS, {
      value: new Map()
    });
  }
  dispatchEvent(event) {
    event.target = event.currentTarget = this;
    if (this['on' + event.type]) {
      try {
        this['on' + event.type](event);
      } catch (err) {
        console.error(err);
      }
    }
    const list = this[EVENTS].get(event.type);
    if (list == null) return;
    list.forEach(handler => {
      try {
        handler.call(this, event);
      } catch (err) {
        console.error(err);
      }
    });
  }
  addEventListener(type, fn) {
    let events = this[EVENTS].get(type);
    if (!events) this[EVENTS].set(type, events = []);
    events.push(fn);
  }
  removeEventListener(type, fn) {
    let events = this[EVENTS].get(type);
    if (events) {
      const index = events.indexOf(fn);
      if (index !== -1) events.splice(index, 1);
    }
  }
}
function Event(type, target) {
  this.type = type;
  this.timeStamp = Date.now();
  this.target = this.currentTarget = this.data = null;
}

// this module is used self-referentially on both sides of the
// thread boundary, but behaves differently in each context.
module.exports = threads.isMainThread ? mainThread() : workerThread();
const baseUrl = URL.pathToFileURL(process.cwd() + '/');
function mainThread() {
  /**
   * A web-compatible Worker implementation atop Node's worker_threads.
   *  - uses DOM-style events (Event.data, Event.type, etc)
   *  - supports event handler properties (worker.onmessage)
   *  - Worker() constructor accepts a module URL
   *  - accepts the {type:'module'} option
   *  - emulates WorkerGlobalScope within the worker
   * @param {string} url  The URL or module specifier to load
   * @param {object} [options]  Worker construction options
   * @param {string} [options.name]  Available as `self.name` within the Worker
   * @param {string} [options.type="classic"]  Pass "module" to create a Module Worker.
   */
  class Worker extends EventTarget {
    constructor(url, options) {
      super();
      const {
        name,
        type
      } = options || {};
      url += '';
      let mod;
      if (/^data:/.test(url)) {
        mod = url;
      } else {
        mod = URL.fileURLToPath(new URL.URL(url, baseUrl));
      }
      const worker = new threads.Worker(__filename, {
        workerData: {
          mod,
          name,
          type
        }
      });
      Object.defineProperty(this, WORKER, {
        value: worker
      });
      worker.on('message', data => {
        const event = new Event('message');
        event.data = data;
        this.dispatchEvent(event);
      });
      worker.on('error', error => {
        error.type = 'error';
        this.dispatchEvent(error);
      });
      worker.on('exit', () => {
        this.dispatchEvent(new Event('close'));
      });
    }
    postMessage(data, transferList) {
      this[WORKER].postMessage(data, transferList);
    }
    terminate() {
      this[WORKER].terminate();
    }
  }
  Worker.prototype.onmessage = Worker.prototype.onerror = Worker.prototype.onclose = null;
  return Worker;
}
function workerThread() {
  let {
    mod,
    name,
    type
  } = threads.workerData || {};
  if (!mod) return mainThread();

  // turn global into a mock WorkerGlobalScope
  const self = global.self = global;

  // enqueue messages to dispatch after modules are loaded
  let q = [];
  function flush() {
    const buffered = q;
    q = null;
    buffered.forEach(event => {
      self.dispatchEvent(event);
    });
  }
  threads.parentPort.on('message', data => {
    const event = new Event('message');
    event.data = data;
    if (q == null) self.dispatchEvent(event);else q.push(event);
  });
  threads.parentPort.on('error', err => {
    err.type = 'Error';
    self.dispatchEvent(err);
  });
  class WorkerGlobalScope extends EventTarget {
    postMessage(data, transferList) {
      threads.parentPort.postMessage(data, transferList);
    }
    // Emulates https://developer.mozilla.org/en-US/docs/Web/API/DedicatedWorkerGlobalScope/close
    close() {
      process.exit();
    }
  }
  let proto = Object.getPrototypeOf(global);
  delete proto.constructor;
  Object.defineProperties(WorkerGlobalScope.prototype, proto);
  proto = Object.setPrototypeOf(global, new WorkerGlobalScope());
  ['postMessage', 'addEventListener', 'removeEventListener', 'dispatchEvent'].forEach(fn => {
    proto[fn] = proto[fn].bind(global);
  });
  global.name = name;
  const isDataUrl = /^data:/.test(mod);
  if (type === 'module') {
    import(mod).catch(err => {
      if (isDataUrl && err.message === 'Not supported') {
        console.warn('Worker(): Importing data: URLs requires Node 12.10+. Falling back to classic worker.');
        return evaluateDataUrl(mod, name);
      }
      console.error(err);
    }).then(flush);
  } else {
    try {
      if (/^data:/.test(mod)) {
        evaluateDataUrl(mod, name);
      } else {
        require(mod);
      }
    } catch (err) {
      console.error(err);
    }
    Promise.resolve().then(flush);
  }
}
function evaluateDataUrl(url, name) {
  const {
    data
  } = parseDataUrl(url);
  return VM.runInThisContext(data, {
    filename: 'worker.<' + (name || 'data:') + '>'
  });
}
function parseDataUrl(url) {
  let [m, type, encoding, data] = url.match(/^data: *([^;,]*)(?: *; *([^,]*))? *,(.*)$/) || [];
  if (!m) throw Error('Invalid Data URL.');
  if (encoding) switch (encoding.toLowerCase()) {
    case 'base64':
      data = Buffer.from(data, 'base64').toString();
      break;
    default:
      throw Error('Unknown Data URL encoding "' + encoding + '"');
  }
  return {
    type,
    data
  };
}