'use strict';

/**
 * @namespace Chart.helpers
 */
var helpers = {
	/**
	 * An empty function that can be used, for example, for optional callback.
	 */
	noop: function() {},

	/**
	 * Returns a unique id, sequentially generated from a global variable.
	 * @returns {Number}
	 * @function
	 */
	uid: (function() {
		var id = 0;
		return function() {
			return id++;
		};
	}()),

	/**
	 * Returns true if `value` is neither null nor undefined, else returns false.
	 * @param {*} value - The value to test.
	 * @returns {Boolean}
	 * @since 2.7.0
	 */
	isNullOrUndef: function(value) {
		return value === null || typeof value === 'undefined';
	},

	/**
	 * Returns true if `value` is an array, else returns false.
	 * @param {*} value - The value to test.
	 * @returns {Boolean}
	 * @function
	 */
	isArray: Array.isArray ? Array.isArray : function(value) {
		return Object.prototype.toString.call(value) === '[object Array]';
	},

	/**
	 * Returns true if `value` is an object (excluding null), else returns false.
	 * @param {*} value - The value to test.
	 * @returns {Boolean}
	 * @since 2.7.0
	 */
	isObject: function(value) {
		return value !== null && Object.prototype.toString.call(value) === '[object Object]';
	},

	/**
	 * Returns `value` if defined, else returns `defaultValue`.
	 * @param {*} value - The value to return if defined.
	 * @param {*} defaultValue - The value to return if `value` is undefined.
	 * @returns {*}
	 */
	valueOrDefault: function(value, defaultValue) {
		return typeof value === 'undefined' ? defaultValue : value;
	},

	/**
	 * Returns value at the given `index` in array if defined, else returns `defaultValue`.
	 * @param {Array} value - The array to lookup for value at `index`.
	 * @param {Number} index - The index in `value` to lookup for value.
	 * @param {*} defaultValue - The value to return if `value[index]` is undefined.
	 * @returns {*}
	 */
	valueAtIndexOrDefault: function(value, index, defaultValue) {
		return helpers.valueOrDefault(helpers.isArray(value) ? value[index] : value, defaultValue);
	},

	/**
	 * Calls `fn` with the given `args` in the scope defined by `thisArg` and returns the
	 * value returned by `fn`. If `fn` is not a function, this method returns undefined.
	 * @param {Function} fn - The function to call.
	 * @param {Array|undefined|null} args - The arguments with which `fn` should be called.
	 * @param {Object} [thisArg] - The value of `this` provided for the call to `fn`.
	 * @returns {*}
	 */
	callback: function(fn, args, thisArg) {
		if (fn && typeof fn.call === 'function') {
			return fn.apply(thisArg, args);
		}
	},

	/**
	 * Note(SB) for performance sake, this method should only be used when loopable type
	 * is unknown or in none intensive code (not called often and small loopable). Else
	 * it's preferable to use a regular for() loop and save extra function calls.
	 * @param {Object|Array} loopable - The object or array to be iterated.
	 * @param {Function} fn - The function to call for each item.
	 * @param {Object} [thisArg] - The value of `this` provided for the call to `fn`.
	 * @param {Boolean} [reverse] - If true, iterates backward on the loopable.
	 */
	each: function(loopable, fn, thisArg, reverse) {
		var i, len, keys;
		if (helpers.isArray(loopable)) {
			len = loopable.length;
			if (reverse) {
				for (i = len - 1; i >= 0; i--) {
					fn.call(thisArg, loopable[i], i);
				}
			} else {
				for (i = 0; i < len; i++) {
					fn.call(thisArg, loopable[i], i);
				}
			}
		} else if (helpers.isObject(loopable)) {
			keys = Object.keys(loopable);
			len = keys.length;
			for (i = 0; i < len; i++) {
				fn.call(thisArg, loopable[keys[i]], keys[i]);
			}
		}
	},

	/**
	 * Returns true if the `a0` and `a1` arrays have the same content, else returns false.
	 * @see http://stackoverflow.com/a/14853974
	 * @param {Array} a0 - The array to compare
	 * @param {Array} a1 - The array to compare
	 * @returns {Boolean}
	 */
	arrayEquals: function(a0, a1) {
		var i, ilen, v0, v1;

		if (!a0 || !a1 || a0.length !== a1.length) {
			return false;
		}

		for (i = 0, ilen = a0.length; i < ilen; ++i) {
			v0 = a0[i];
			v1 = a1[i];

			if (v0 instanceof Array && v1 instanceof Array) {
				if (!helpers.arrayEquals(v0, v1)) {
					return false;
				}
			} else if (v0 !== v1) {
				// NOTE: two different object instances will never be equal: {x:20} != {x:20}
				return false;
			}
		}

		return true;
	},

	/**
	 * Returns a deep copy of `source` without keeping references on objects and arrays.
	 * @param {*} source - The value to clone.
	 * @returns {*}
	 */
	clone: function(source) {
		if (helpers.isArray(source)) {
			return source.map(helpers.clone);
		}

		if (helpers.isObject(source)) {
			var target = {};
			var keys = Object.keys(source);
			var klen = keys.length;
			var k = 0;

			for (; k < klen; ++k) {
				target[keys[k]] = helpers.clone(source[keys[k]]);
			}

			return target;
		}

		return source;
	},

	/**
	 * The default merger when Chart.helpers.merge is called without merger option.
	 * Note(SB): this method is also used by configMerge and scaleMerge as fallback.
	 * @private
	 */
	_merger: function(key, target, source, options) {
		var tval = target[key];
		var sval = source[key];

		if (helpers.isObject(tval) && helpers.isObject(sval)) {
			helpers.merge(tval, sval, options);
		} else {
			target[key] = helpers.clone(sval);
		}
	},

	/**
	 * Merges source[key] in target[key] only if target[key] is undefined.
	 * @private
	 */
	_mergerIf: function(key, target, source) {
		var tval = target[key];
		var sval = source[key];

		if (helpers.isObject(tval) && helpers.isObject(sval)) {
			helpers.mergeIf(tval, sval);
		} else if (!target.hasOwnProperty(key)) {
			target[key] = helpers.clone(sval);
		}
	},

	/**
	 * Recursively deep copies `source` properties into `target` with the given `options`.
	 * IMPORTANT: `target` is not cloned and will be updated with `source` properties.
	 * @param {Object} target - The target object in which all sources are merged into.
	 * @param {Object|Array(Object)} source - Object(s) to merge into `target`.
	 * @param {Object} [options] - Merging options:
	 * @param {Function} [options.merger] - The merge method (key, target, source, options)
	 * @returns {Object} The `target` object.
	 */
	merge: function(target, source, options) {
		var sources = helpers.isArray(source) ? source : [source];
		var ilen = sources.length;
		var merge, i, keys, klen, k;

		if (!helpers.isObject(target)) {
			return target;
		}

		options = options || {};
		merge = options.merger || helpers._merger;

		for (i = 0; i < ilen; ++i) {
			source = sources[i];
			if (!helpers.isObject(source)) {
				continue;
			}

			keys = Object.keys(source);
			for (k = 0, klen = keys.length; k < klen; ++k) {
				merge(keys[k], target, source, options);
			}
		}

		return target;
	},

	/**
	 * Recursively deep copies `source` properties into `target` *only* if not defined in target.
	 * IMPORTANT: `target` is not cloned and will be updated with `source` properties.
	 * @param {Object} target - The target object in which all sources are merged into.
	 * @param {Object|Array(Object)} source - Object(s) to merge into `target`.
	 * @returns {Object} The `target` object.
	 */
	mergeIf: function(target, source) {
		return helpers.merge(target, source, {merger: helpers._mergerIf});
	}
};

module.exports = helpers;

// DEPRECATIONS

/**
 * Provided for backward compatibility, use Chart.helpers.callback instead.
 * @function Chart.helpers.callCallback
 * @deprecated since version 2.6.0
 * @todo remove at version 3
 * @private
 */
helpers.callCallback = helpers.callback;

/**
 * Provided for backward compatibility, use Array.prototype.indexOf instead.
 * Array.prototype.indexOf compatibility: Chrome, Opera, Safari, FF1.5+, IE9+
 * @function Chart.helpers.indexOf
 * @deprecated since version 2.7.0
 * @todo remove at version 3
 * @private
 */
helpers.indexOf = function(array, item, fromIndex) {
	return Array.prototype.indexOf.call(array, item, fromIndex);
};

/**
 * Provided for backward compatibility, use Chart.helpers.valueOrDefault instead.
 * @function Chart.helpers.getValueOrDefault
 * @deprecated since version 2.7.0
 * @todo remove at version 3
 * @private
 */
helpers.getValueOrDefault = helpers.valueOrDefault;

/**
 * Provided for backward compatibility, use Chart.helpers.valueAtIndexOrDefault instead.
 * @function Chart.helpers.getValueAtIndexOrDefault
 * @deprecated since version 2.7.0
 * @todo remove at version 3
 * @private
 */
helpers.getValueAtIndexOrDefault = helpers.valueAtIndexOrDefault;
