(function (ns) {

    var Bird = ns.Bird = Hilo.Class.create({
        Extends: Hilo.Sprite,
        constructor: function (properties) {
            Bird.superclass.constructor.call(this, properties);

            this.addFrame(properties.atlas.getSprite('bird'));
            this.interval = 6;
            this.pivotX = 43;
            this.pivotY = 30;

            this.gravity = 10 / 1000 * 0.3;
            this.flyHeight = 80;
            this.initVelocity = Math.sqrt(2 * this.flyHeight * this.gravity);
        },

        startX: 0, //小鸟的起始x坐标
        startY: 0, //小鸟的起始y坐标
        groundY: 0, //地面的坐标
        gravity: 0, //重力加速度
        flyHeight: 0, //小鸟每次往上飞的高度
        initVelocity: 0, //小鸟往上飞的初速度

        isDead: true, //小鸟是否已死亡
        isUp: false, //小鸟是在往上飞阶段，还是下落阶段
        flyStartY: 0, //小鸟往上飞的起始y轴坐标
        flyStartTime: 0, //小鸟飞行起始时间

        getReady: function () {
            //设置起始坐标
            this.x = this.startX;
            this.y = this.startY;

            this.rotation = 0;
            this.interval = 6;
            this.play();
            this.tween = Hilo.Tween.to(this, { y: this.y + 10, rotation: -8 }, { duration: 400, reverse: true, loop: true });
        },

        startFly: function () {
            this.isDead = false;
            this.interval = 3;
            this.flyStartY = this.y;
            this.flyStartTime = +new Date();
            if (this.tween) this.tween.stop();
        },

        onUpdate: function () {
            if (this.isDead) return;

            //飞行时间
            var time = (+new Date()) - this.flyStartTime;
            //飞行距离
            var distance = this.initVelocity * time - 0.5 * this.gravity * time * time;
            //y轴坐标
            var y = this.flyStartY - distance;

            if (y <= this.groundY) {
                //小鸟未落地
                this.y = y;
                if (distance > 0 && !this.isUp) {
                    //往上飞时，角度上仰20度
                    this.tween = Hilo.Tween.to(this, { rotation: -20 }, { duration: 200 });
                    this.isUp = true;
                } else if (distance < 0 && this.isUp) {
                    //往下跌落时，角度往下90度
                    this.tween = Hilo.Tween.to(this, { rotation: 90 }, { duration: this.groundY - this.y });
                    this.isUp = false;
                }
            } else {
                //小鸟已经落地，即死亡
                this.y = this.groundY;
                this.isDead = true;
            }
        }
    });

})(window.game);