(function() {
  const isCommonJS = typeof module !== 'undefined' && module.exports;
  const isNode = !(typeof window !== 'undefined' && this === window);
  var setImmediate =
    setImmediate ||
    function(cb) {
      setTimeout(cb, 0);
    };
  const Worker = isNode ? require(`${__dirname}/Worker.js`) : self.Worker;
  const URL =
    typeof self !== 'undefined' ? (self.URL ? self.URL : self.webkitURL) : null;
  const _supports = !!(isNode || self.Worker); // node always supports parallel

  function extend(from, to) {
    if (!to) to = {};
    for (const i in from) {
      if (to[i] === undefined) to[i] = from[i];
    }
    return to;
  }

  function Operation() {
    this._callbacks = [];
    this._errCallbacks = [];

    this._resolved = 0;
    this._result = null;
  }

  Operation.prototype.resolve = function(err, res) {
    if (!err) {
      this._resolved = 1;
      this._result = res;

      for (let i = 0; i < this._callbacks.length; ++i) {
        this._callbacks[i](res);
      }
    } else {
      this._resolved = 2;
      this._result = err;

      for (let iE = 0; iE < this._errCallbacks.length; ++iE) {
        this._errCallbacks[iE](err);
      }
    }

    this._callbacks = [];
    this._errCallbacks = [];
  };

  Operation.prototype.then = function(cb, errCb) {
    if (this._resolved === 1) {
      // result
      if (cb) {
        cb(this._result);
      }

      return;
    }
    if (this._resolved === 2) {
      // error
      if (errCb) {
        errCb(this._result);
      }
      return;
    }

    if (cb) {
      this._callbacks[this._callbacks.length] = cb;
    }

    if (errCb) {
      this._errCallbacks[this._errCallbacks.length] = errCb;
    }
    return this;
  };

  const defaults = {
    evalPath: isNode ? `${__dirname}/eval.js` : null,
    maxWorkers: isNode
      ? require('os').cpus().length
      : navigator.hardwareConcurrency || 4,
    synchronous: true,
    env: {},
    envNamespace: 'env'
  };

  function Parallel(data, options) {
    this.data = data;
    this.options = extend(defaults, options);
    this.operation = new Operation();
    this.operation.resolve(null, this.data);
    this.requiredScripts = [];
    this.requiredFunctions = [];
  }

  // static method
  Parallel.isSupported = function() {
    return _supports;
  };

  Parallel.prototype.getWorkerSource = function(cb, env) {
    const that = this;
    let preStr = '';
    let i = 0;
    if (!isNode && this.requiredScripts.length !== 0) {
      preStr += `importScripts("${this.requiredScripts.join('","')}");\r\n`;
    }

    for (i = 0; i < this.requiredFunctions.length; ++i) {
      if (this.requiredFunctions[i].name) {
        preStr += `var ${
          this.requiredFunctions[i].name
        } = ${this.requiredFunctions[i].fn.toString()};`;
      } else {
        preStr += this.requiredFunctions[i].fn.toString();
      }
    }

    env = JSON.stringify(env || {});

    const ns = this.options.envNamespace;

    if (isNode) {
      return `${preStr}process.on("message", function(e) {global.${ns} = ${env};process.send(JSON.stringify((${cb.toString()})(JSON.parse(e).data)))})`;
    }
    return `${preStr}self.onmessage = function(e) {var global = {}; global.${ns} = ${env};self.postMessage((${cb.toString()})(e.data))}`;
  };

  Parallel.prototype.require = function() {
    const args = Array.prototype.slice.call(arguments, 0);
    let func;

    for (let i = 0; i < args.length; i++) {
      func = args[i];

      if (typeof func === 'string') {
        this.requiredScripts.push(func);
      } else if (typeof func === 'function') {
        this.requiredFunctions.push({ fn: func });
      } else if (typeof func === 'object') {
        this.requiredFunctions.push(func);
      }
    }

    return this;
  };

  Parallel.prototype._spawnWorker = function(cb, env) {
    let wrk;
    const src = this.getWorkerSource(cb, env);
    if (isNode) {
      wrk = new Worker(this.options.evalPath);
      wrk.postMessage(src);
    } else {
      if (Worker === undefined) {
        return undefined;
      }

      try {
        if (this.requiredScripts.length !== 0) {
          if (this.options.evalPath !== null) {
            wrk = new Worker(this.options.evalPath);
            wrk.postMessage(src);
          } else {
            throw new Error("Can't use required scripts without eval.js!");
          }
        } else if (!URL) {
          throw new Error("Can't create a blob URL in this browser!");
        } else {
          const blob = new Blob([src], { type: 'text/javascript' });
          const url = URL.createObjectURL(blob);

          wrk = new Worker(url);
        }
      } catch (e) {
        if (this.options.evalPath !== null) {
          // blob/url unsupported, cross-origin error
          wrk = new Worker(this.options.evalPath);
          wrk.postMessage(src);
        } else {
          throw e;
        }
      }
    }

    return wrk;
  };

  Parallel.prototype.spawn = function(cb, env) {
    const that = this;
    const newOp = new Operation();
    let timeout;

    env = extend(this.options.env, env || {});

    this.operation.then(() => {

      if(env.timeout) {
        timeout = setTimeout(function() {
          if(!newOp.resolved) {
            wrk.terminate();
            newOp.resolve(new Error('Operation timed out!'), null);
          }
        }, env.timeout);
      }
      
      const wrk = that._spawnWorker(cb, env);
      if (wrk !== undefined) {
        wrk.onmessage = function(msg) {
          if(timeout) clearTimeout(timeout);
          wrk.terminate();
          that.data = msg.data;
          newOp.resolve(null, that.data);
        };
        wrk.onerror = function(e) {
          if(timeout) clearTimeout(timeout);
          wrk.terminate();
          newOp.resolve(e, null);
        };
        wrk.postMessage(that.data);
      } else if (that.options.synchronous) {
        setImmediate(() => {
          try {
            that.data = cb(that.data);
            newOp.resolve(null, that.data);
          } catch (e) {
            newOp.resolve(e, null);
          }
        });
      } else {
        throw new Error(
          'Workers do not exist and synchronous operation not allowed!'
        );
      }
    });
    this.operation = newOp;
    return this;
  };

  Parallel.prototype._spawnMapWorker = function(i, cb, done, env, wrk) {
    const that = this;

    if (!wrk) wrk = that._spawnWorker(cb, env);

    if (wrk !== undefined) {
      wrk.onmessage = function(msg) {
        that.data[i] = msg.data;
        done(null, wrk);
      };
      wrk.onerror = function(e) {
        wrk.terminate();
        done(e);
      };
      wrk.postMessage(that.data[i]);
    } else if (that.options.synchronous) {
      setImmediate(() => {
        that.data[i] = cb(that.data[i]);
        done();
      });
    } else {
      throw new Error(
        'Workers do not exist and synchronous operation not allowed!'
      );
    }
  };

  Parallel.prototype.map = function(cb, env) {
    env = extend(this.options.env, env || {});

    if (!this.data.length) {
      return this.spawn(cb, env);
    }

    const that = this;
    let startedOps = 0;
    let doneOps = 0;
    function done(err, wrk) {
      if (err) {
        newOp.resolve(err, null);
      } else if (++doneOps === that.data.length) {
        newOp.resolve(null, that.data);
        if (wrk) wrk.terminate();
      } else if (startedOps < that.data.length) {
        that._spawnMapWorker(startedOps++, cb, done, env, wrk);
      } else if (wrk) wrk.terminate();
    }

    var newOp = new Operation();
    this.operation.then(
      () => {
        for (
          ;
          startedOps - doneOps < that.options.maxWorkers &&
          startedOps < that.data.length;
          ++startedOps
        ) {
          that._spawnMapWorker(startedOps, cb, done, env);
        }
      },
      err => {
        newOp.resolve(err, null);
      }
    );
    this.operation = newOp;
    return this;
  };

  Parallel.prototype._spawnReduceWorker = function(data, cb, done, env, wrk) {
    const that = this;
    if (!wrk) wrk = that._spawnWorker(cb, env);

    if (wrk !== undefined) {
      wrk.onmessage = function(msg) {
        that.data[that.data.length] = msg.data;
        done(null, wrk);
      };
      wrk.onerror = function(e) {
        wrk.terminate();
        done(e, null);
      };
      wrk.postMessage(data);
    } else if (that.options.synchronous) {
      setImmediate(() => {
        that.data[that.data.length] = cb(data);
        done();
      });
    } else {
      throw new Error(
        'Workers do not exist and synchronous operation not allowed!'
      );
    }
  };

  Parallel.prototype.reduce = function(cb, env) {
    env = extend(this.options.env, env || {});

    if (!this.data.length) {
      throw new Error("Can't reduce non-array data");
    }

    let runningWorkers = 0;
    const that = this;
    function done(err, wrk) {
      --runningWorkers;
      if (err) {
        newOp.resolve(err, null);
      } else if (that.data.length === 1 && runningWorkers === 0) {
        that.data = that.data[0];
        newOp.resolve(null, that.data);
        if (wrk) wrk.terminate();
      } else if (that.data.length > 1) {
        ++runningWorkers;
        that._spawnReduceWorker(
          [that.data[0], that.data[1]],
          cb,
          done,
          env,
          wrk
        );
        that.data.splice(0, 2);
      } else if (wrk) wrk.terminate();
    }

    var newOp = new Operation();
    this.operation.then(() => {
      if (that.data.length === 1) {
        newOp.resolve(null, that.data[0]);
      } else {
        for (
          var i = 0;
          i < that.options.maxWorkers && i < Math.floor(that.data.length / 2);
          ++i
        ) {
          ++runningWorkers;
          that._spawnReduceWorker(
            [that.data[i * 2], that.data[i * 2 + 1]],
            cb,
            done,
            env
          );
        }

        that.data.splice(0, i * 2);
      }
    });
    this.operation = newOp;
    return this;
  };

  Parallel.prototype.then = function(cb, errCb) {
    const that = this;
    const newOp = new Operation();
    errCb = typeof errCb === 'function' ? errCb : function() {};

    this.operation.then(
      () => {
        let retData;

        try {
          if (cb) {
            retData = cb(that.data);
            if (retData !== undefined) {
              that.data = retData;
            }
          }
          newOp.resolve(null, that.data);
        } catch (e) {
          if (errCb) {
            retData = errCb(e);
            if (retData !== undefined) {
              that.data = retData;
            }

            newOp.resolve(null, that.data);
          } else {
            newOp.resolve(null, e);
          }
        }
      },
      err => {
        if (errCb) {
          const retData = errCb(err);
          if (retData !== undefined) {
            that.data = retData;
          }

          newOp.resolve(null, that.data);
        } else {
          newOp.resolve(null, err);
        }
      }
    );
    this.operation = newOp;
    return this;
  };

  if (isCommonJS) {
    module.exports = Parallel;
  } else {
    self.Parallel = Parallel;
  }
})();