pastafarian.js

;(function (root) {
  function ITE(prev, next) {
    var error = Error.call(this, 'Transition from ' + prev + ' to ' + next + ' is not allowed');
    error.name = 'IllegalTransitionException';
    error.prev = prev;
    error.attempt = next;
    return error;
  }

  function FSM(config) {
    var events = {};
    var fsm = {
      transitions : config.states,
      current     : config.initial,
      error       : config.error,
    };
    fsm.bind = function(evt, fn) {
      events[evt] = events[evt] || [];
      events[evt] = events[evt].concat(fn);
      return fsm;
    };
    fsm.unbind = function(evt, fn) {
      if (evt in events && events[evt].indexOf(fn) > -1)
        events[evt].splice(events[evt].indexOf(fn), 1);
      return fsm;
    };
    fsm.on = fsm.bind;

    function onError(args) {
      if (typeof fsm.error === 'function')
        fsm.error.apply(this, args);
      else
        throw args[0];
    }

    function emit(evt, args) {
      if (evt in events) {
        for (var i = 0; i < events[evt].length; ++i) {
          try {
            events[evt][i].apply(this, args);
          } catch (e) {
            onError([e]);
          }
        }
      }
    };

    fsm.go = function(next) {
      var prev = fsm.current;
      var params = Array.prototype.slice.call(arguments, 1);

      if (fsm.transitions[prev].indexOf(next) > -1) {
        emit('after:' + prev, [next].concat(params));
        emit('before:' + next, [prev].concat(params));
        fsm.current = next;
        emit(next, [prev].concat(params));
        emit('*', [prev, next].concat(params));
      } else {
        onError([new ITE(prev, next), prev, next].concat(params));
      }
      return fsm;
    };

    return fsm;
  }

  if (typeof define == 'function' && typeof define.amd == 'object' && define.amd) {
    define(function () { return FSM; });
  } else if (typeof module === 'object' && module.exports) {
    module.exports = FSM;
  } else if (typeof self !== 'undefined') {
    self.StateMachine = FSM;
  } else {
    root.StateMachine = FSM;
  }
}(this));