(function() {

    if(typeof libutil!="object") {
        if(typeof loadfail=="function") {
            loadfail("libtransition.js：object libutil(type of "+(typeof libutil)+") is not defined");
        } else {
            window.alert("libtransition.js：object libutil is not defined");
        }
        return;
    }

    if(typeof Bezier!="function") {
        if(typeof loadfail=="function") {
            loadfail("libtransition.js：class Bezier(type of "+(typeof Bezier)+") is not defined");
        } else {
            window.alert("libtransition.js：class Bezier is not defined");
        }
        return;
    }

    if(typeof requestAnimationFrame!="function") {
        if(typeof loadfail=="function") {
            loadfail("libtransition.js：function requestAnimationFrame(type of "+(typeof requestAnimationFrame)+") is not defined");
        } else {
            window.alert("libtransition.js：function requestAnimationFrame is not defined");
        }
        return;
    }

    class Transition {

        static linear=new Bezier(0, 0, 1, 1);

        constructor() {
            // static fields (set by user)
            this.obj = null;
            this.key = null;
            this.startval = 0.0;
            this.endval = 0.0;
            this.duration = 0;
            this.animfunc = Transition.linear;
            this.stoponend=true;
            this.onend = null;
            // dynamic fields (set by this program)
            this.elapsed = 0;
            this.carryover = 0;
        }

        start() {
            this.stop();
            transition_update_list.push(this);
        }

        stop() {
            var index=-1;
            do {
                index = transition_update_list.indexOf(this);
                if(index > -1) {
                    transition_update_list.splice(index, 1);
                }
            } while(index!=-1);
        }

        update(et) {
            if(window.EnableDebugMode) {
                if(!(this.key in this.obj)) {
                    this.stop();
                    console.error("the key", this.key, "is not in the obj", this.obj);
                    return;
                }
                if(typeof this.animfunc!="function") {
                    this.stop();
                    console.error("(a instance of transition).animfunc is not a function");
                    return;
                }
                if(!libutil.isNumber(et)) {
                    et=0;
                }
            }
            // this.carryover is for this.onend() only, not for the animation itself
            this.carryover=0;
            this.elapsed+=et;
            if(this.elapsed>=this.duration) {
                this.carryover=this.elapsed-this.duration;
                this.elapsed=this.duration;
                this.obj[this.key]=this.endval;
                if(this.onend!==null&&typeof this.onend=="function") {
                    try {
                        this.onend();
                    } catch(e) {
                        console.error(e);
                    }
                }
                if(this.stoponend) {
                    this.stop();
                }
                return;
            }
            this.obj[this.key]=(this.endval-this.startval)*libutil.clamp(this.animfunc(this.elapsed/this.duration), 0, 1);
        }

    }

    var transition_update_list=[];

    var ticker_lasttime=Date.now();

    var run_ticker=function(ts) {
        requestAnimationFrame(run_ticker);
        var et = ts - ticker_lasttime;
        ticker_lasttime = ts;
        transition_update_list.forEach(function(elem) {
            elem.update(et);
        });
    };

    run_ticker(ticker_lasttime);

    window.Transition=Transition;
})();