/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements.  See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership.  The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License.  You may obtain a copy of the License at
*
*   http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied.  See the License for the
* specific language governing permissions and limitations
* under the License.
*/

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.
 */
export function throttle(fn, delay, debounce) {
	var currCall;
	var lastCall = 0;
	var lastExec = 0;
	var timer = null;
	var diff;
	var scope;
	var args;
	var debounceNextCall;

	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;
		var thisDelay = debounceNextCall || delay;
		var thisDebounce = debounceNextCall || debounce;
		debounceNextCall = null;
		diff = currCall - (thisDebounce ? lastCall : lastExec) - thisDelay;

		clearTimeout(timer);

		// Here we should make sure that: the `exec` SHOULD NOT be called later
		// than a new call of `cb`, that is, preserving the command order. Consider
		// calculating "scale rate" when roaming as an example. When a call of `cb`
		// happens, either the `exec` is called dierectly, or the call is delayed.
		// But the delayed call should never be later than next call of `cb`. Under
		// this assurance, we can simply update view state each time `dispatchAction`
		// triggered by user roaming, but not need to add extra code to avoid the
		// state being "rolled-back".
		if (thisDebounce) {
			timer = setTimeout(exec, thisDelay);
		} else {
			if (diff >= 0) {
				exec();
			} else {
				timer = setTimeout(exec, -diff);
			}
		}

		lastCall = currCall;
	};

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

	/**
     * Enable debounce once.
     */
	cb.debounceNextCall = function(debounceDelay) {
		debounceNextCall = debounceDelay;
	};

	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.
 */
export function createOrUpdate(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] = 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
 */
export function clear(obj, fnAttr) {
	var fn = obj[fnAttr];
	if (fn && fn[ORIGIN_METHOD]) {
		obj[fnAttr] = fn[ORIGIN_METHOD];
	}
}