(function (window) {

  StateMachine = {

    //---------------------------------------------------------------------------

    VERSION: "2.1.0",

    //---------------------------------------------------------------------------

    Result: {
      SUCCEEDED:    1, // the event transitioned successfully from one state to another
      NOTRANSITION: 2, // the event was successfull but no state transition was necessary
      CANCELLED:    3, // the event was cancelled by the caller in a beforeEvent callback
      ASYNC:        4, // the event is asynchronous and the caller is in control of when the transition occurs
    },

    Error: {
      INVALID_TRANSITION: 100, // caller tried to fire an event that was innapropriate in the current state
      PENDING_TRANSITION: 200, // caller tried to fire an event while an async transition was still pending
      INVALID_CALLBACK:   300, // caller provided callback function threw an exception
    },

    WILDCARD: '*',
    ASYNC: 'async',

    //---------------------------------------------------------------------------

    create: function(cfg, target) {

      var initial   = (typeof cfg.initial == 'string') ? { state: cfg.initial } : cfg.initial; // allow for a simple string, or an object with { state: 'foo', event: 'setup', defer: true|false }
      var fsm       = target || cfg.target  || {};
      var events    = cfg.events || [];
      var callbacks = cfg.callbacks || {};
      var map       = {};

      var add = function(e) {
        var from = (e.from instanceof Array) ? e.from : (e.from ? [e.from] : [StateMachine.WILDCARD]); // allow 'wildcard' transition if 'from' is not specified
        map[e.name] = map[e.name] || {};
        for (var n = 0 ; n < from.length ; n++)
          map[e.name][from[n]] = e.to || from[n]; // allow no-op transition if 'to' is not specified
      };

      if (initial) {
        initial.event = initial.event || 'startup';
        add({ name: initial.event, from: 'none', to: initial.state });
      }

      for(var n = 0 ; n < events.length ; n++)
        add(events[n]);

      for(var name in map) {
        if (map.hasOwnProperty(name))
          fsm[name] = StateMachine.buildEvent(name, map[name]);
      }

      for(var name in callbacks) {
        if (callbacks.hasOwnProperty(name))
          fsm[name] = callbacks[name]
      }

      fsm.current = 'none';
      fsm.is      = function(state) { return this.current == state; };
      fsm.can     = function(event) { return !this.transition && (map[event].hasOwnProperty(this.current) || map[event].hasOwnProperty(StateMachine.WILDCARD)); }
      fsm.cannot  = function(event) { return !this.can(event); };
      fsm.error   = cfg.error || function(name, from, to, args, error, msg) { throw msg; }; // default behavior when something unexpected happens is to throw an exception, but caller can override this behavior if desired (see github issue #3)

      if (initial && !initial.defer)
        fsm[initial.event]();

      return fsm;

    },

    //===========================================================================

    doCallback: function(fsm, func, name, from, to, args) {
      if (func) {
        try {
          return func.apply(fsm, [name, from, to].concat(args));
        }
        catch(e) {
          return fsm.error(name, from, to, args, StateMachine.Error.INVALID_CALLBACK, "an exception occurred in a caller-provided callback function");
        }
      }
    },

    beforeEvent: function(fsm, name, from, to, args) { return StateMachine.doCallback(fsm, fsm['onbefore' + name],                     name, from, to, args); },
    afterEvent:  function(fsm, name, from, to, args) { return StateMachine.doCallback(fsm, fsm['onafter'  + name] || fsm['on' + name], name, from, to, args); },
    leaveState:  function(fsm, name, from, to, args) { return StateMachine.doCallback(fsm, fsm['onleave'  + from],                     name, from, to, args); },
    enterState:  function(fsm, name, from, to, args) { return StateMachine.doCallback(fsm, fsm['onenter'  + to]   || fsm['on' + to],   name, from, to, args); },
    changeState: function(fsm, name, from, to, args) { return StateMachine.doCallback(fsm, fsm['onchangestate'],                       name, from, to, args); },


    buildEvent: function(name, map) {
      return function() {

        var from  = this.current;
        var to    = map[from] || map[StateMachine.WILDCARD] || from;
        var args  = Array.prototype.slice.call(arguments); // turn arguments into pure array

        if (this.transition)
          return this.error(name, from, to, args, StateMachine.Error.PENDING_TRANSITION, "event " + name + " inappropriate because previous transition did not complete");

        if (this.cannot(name))
          return this.error(name, from, to, args, StateMachine.Error.INVALID_TRANSITION, "event " + name + " inappropriate in current state " + this.current);

        if (false === StateMachine.beforeEvent(this, name, from, to, args))
          return StateMachine.CANCELLED;

        if (from === to) {
          StateMachine.afterEvent(this, name, from, to, args);
          return StateMachine.NOTRANSITION;
        }

        // prepare a transition method for use EITHER lower down, or by caller if they want an async transition (indicated by an ASYNC return value from leaveState)
        var fsm = this;
        this.transition = function() {
          fsm.transition = null; // this method should only ever be called once
          fsm.current = to;
          StateMachine.enterState( fsm, name, from, to, args);
          StateMachine.changeState(fsm, name, from, to, args);
          StateMachine.afterEvent( fsm, name, from, to, args);
        };

        var leave = StateMachine.leaveState(this, name, from, to, args);
        if (false === leave) {
          this.transition = null;
          return StateMachine.CANCELLED;
        }
        else if ("async" === leave) {
          return StateMachine.ASYNC;
        }
        else {
          if (this.transition)
            this.transition(); // in case user manually called transition() but forgot to return ASYNC
          return StateMachine.SUCCEEDED;
        }

      };
    }

  }; // StateMachine

  //===========================================================================

  if ("function" === typeof define) {
    define("statemachine", [], function() { return StateMachine; });
  }
  else {
    window.StateMachine = StateMachine;
  }

}(this));