Chord.TRIGGER_KEY = 17; // ctrl
Chord.MAX_DELAY = 500; // half second or less between chord members

// eg: new Chord("kc");
function Chord(chordWord) {
    chordWord = chordWord.toUpperCase();

    this.members = [];
    
    for (var i = 0; i < chordWord.length; i++)
        this.members[i] = chordWord.charCodeAt(i);

    this.chordWord = chordWord;
    this.onComplete = new Function();
    this.onReset = new Function();

    var self = this;
    var currentMember, currentKey, lockedOn, timerId, started;

    reset();

    this.start = function() {
        ev_attach("keydown", handleKeyDown);
        ev_attach("keyup", handleKeyUp);
    }

    this.stop = function() {
        reset();
        ev_detach("keydown", handleKeyDown);
        ev_detach("keyup", handleKeyUp);
    }

    function handleKeyDown(e) {
        e = ev_fix(e);

        if (e.keyCode == Chord.TRIGGER_KEY) {
            lockedOn = true;
        }
        else if (lockedOn) {
            var number = findInArray(self.members, e.keyCode);

            if (number == currentKey + 1) {
                killResetTimer();

                if (!started) {
                    started = true;
                }

                currentKey = number;
                e.preventDefault();

                if (currentKey == self.members.length - 1) {
                    self.onComplete();
                    reset();
                }

                setResetTimer();
            }
            else if (started) {
                reset();
                self.onReset();
            }
        }
    }

    function handleKeyUp(e) {
        e = ev_fix(e);

        if (e.keyCode == Chord.TRIGGER_KEY) {
            reset();

            if (started) {
                self.onReset();
            }
        }
    }

    function reset() {
        killResetTimer();
        currentMember = -1;
        currentKey = -1;
        lockedOn = false;
        started = false;
        timerId = null;
    }

    function setResetTimer() {
        killResetTimer();
        timerId = window.setTimeout(reset, Chord.MAX_DELAY);
    }

    function killResetTimer() {
        if (timerId != null) {
            window.clearTimeout(timerId);
            timerId = null;
        }
    }

    function findInArray(arr, thing) {
        var l = arr.length;
        
        for (var i = 0; i < l; i++)
            if (arr[i] == thing)
                return i;

        return -1;
    }

    function ev_attach(eventName, fp) {
        if (document.attachEvent) document.attachEvent("on"+eventName, fp);
        else if (document.addEventListener) document.addEventListener(eventName, fp, false);
    }

    function ev_detach(eventName, fp) {
        if (document.detachEvent) document.detachEvent("on"+eventName, fp);
        else if (document.removeEventListener) document.removeEventListener(eventName, fp, false);
    }

    function ev_fix(e) {
        if (!e && window.event) {
            e = window.event;
        }

        if (!e.preventDefault) {
            e.preventDefault = function() {
                this.returnValue = false;
                this.keyCode = 0;
            }
        }

        return e;
    }
}