define(function () {

    var lib = {};

    var ORIGIN_METHOD = '\0__throttleOriginMethod';
    var RATE = '\0__throttleRate';
    var THROTTLE_TYPE = '\0__throttleType';

    /**
     * @public
     * @param {(Function)} fn
     * @param {number} [delay=0] Unit: ms.
     * @param {boolean} [debounce=false]
     *        true: If call interval less than `delay`, only the last call works.
     *        false: If call interval less than `delay, call works on fixed rate.
     * @return {(Function)} throttled fn.
     */
    lib.throttle = function (fn, delay, debounce) {

        var currCall;
        var lastCall = 0;
        var lastExec = 0;
        var timer = null;
        var diff;
        var scope;
        var args;

        delay = delay || 0;

        function exec() {
            lastExec = (new Date()).getTime();
            timer = null;
            fn.apply(scope, args || []);
        }

        var cb = function () {
            currCall = (new Date()).getTime();
            scope = this;
            args = arguments;
            diff = currCall - (debounce ? lastCall : lastExec) - delay;

            clearTimeout(timer);

            if (debounce) {
                timer = setTimeout(exec, delay);
            }
            else {
                if (diff >= 0) {
                    exec();
                }
                else {
                    timer = setTimeout(exec, -diff);
                }
            }

            lastCall = currCall;
        };

        /**
         * Clear throttle.
         * @public
         */
        cb.clear = function () {
            if (timer) {
                clearTimeout(timer);
                timer = null;
            }
        };

        return cb;
    };

    /**
     * Create throttle method or update throttle rate.
     *
     * @example
     * ComponentView.prototype.render = function () {
     *     ...
     *     throttle.createOrUpdate(
     *         this,
     *         '_dispatchAction',
     *         this.model.get('throttle'),
     *         'fixRate'
     *     );
     * };
     * ComponentView.prototype.remove = function () {
     *     throttle.clear(this, '_dispatchAction');
     * };
     * ComponentView.prototype.dispose = function () {
     *     throttle.clear(this, '_dispatchAction');
     * };
     *
     * @public
     * @param {Object} obj
     * @param {string} fnAttr
     * @param {number} [rate]
     * @param {string} [throttleType='fixRate'] 'fixRate' or 'debounce'
     * @return {Function} throttled function.
     */
    lib.createOrUpdate = function (obj, fnAttr, rate, throttleType) {
        var fn = obj[fnAttr];

        if (!fn) {
            return;
        }

        var originFn = fn[ORIGIN_METHOD] || fn;
        var lastThrottleType = fn[THROTTLE_TYPE];
        var lastRate = fn[RATE];

        if (lastRate !== rate || lastThrottleType !== throttleType) {
            if (rate == null || !throttleType) {
                return (obj[fnAttr] = originFn);
            }

            fn = obj[fnAttr] = lib.throttle(
                originFn, rate, throttleType === 'debounce'
            );
            fn[ORIGIN_METHOD] = originFn;
            fn[THROTTLE_TYPE] = throttleType;
            fn[RATE] = rate;
        }

        return fn;
    };

    /**
     * Clear throttle. Example see throttle.createOrUpdate.
     *
     * @public
     * @param {Object} obj
     * @param {string} fnAttr
     */
    lib.clear = function (obj, fnAttr) {
        var fn = obj[fnAttr];
        if (fn && fn[ORIGIN_METHOD]) {
            obj[fnAttr] = fn[ORIGIN_METHOD];
        }
    };

    return lib;
});
