/**
 *
 * Wordpress like hook system for javascript.
 *
 * The purpose of this library is to make code extensible by using hooks like in
 * the Wordpress CMS.
 *
 * The functions in this library shall help other developers hook their code
 * into a generic code using their callbacks.
 *
 * USAGE ------------------------------------------
 *
 * Add filter
 *
 * 		add_filter(tag, callback, priority);
 *
 * Apply filters
 *
 * 		apply_filtes(tag, value, options);
 *
 * ------------------------------------------------
 *
 * Add action
 *
 * 		add_action(tag, callback, priority);
 *
 * Apply action
 *
 * 		apply_filters(tag, options);
 *
 * ------------------------------------------------
 *
 * @author IAmRDhar
 * @ver 1.0
 */

// functional class for hooks
function _jsHooks() {

	// instance
	var _jsH = this;

	// will contain data structure for actions
	this.actions = [];

	// will contain data structure for filters
	this.filters = [];

	// object that contains functions that can
	// be used for adding callbacks to actions
	// and filters with a certain priority
	this.add = {

		action : function(tag, callback, priority) {
			if (typeof priority === "undefined") {
				priority = 10; // default priority
			}

			// empty array if not already initialized
			_jsH.actions[tag] = _jsH.actions[tag] || [];
			// empty array if not already initialized
			_jsh.actions[tag][priority] = _jsH.actions[tag][priority] || [];

			// add callback at the right place in ds
			// with respect to tag and priority
			_jsH.actions[tag][priority].push(callback);
		},

		filter : function(tag, callback, priority) {
			if (typeof priority === "undefined") {
				priority = 10;
			}

			// empty array if not already initialized
			_jsH.filters[tag] = _jsH.filters[tag] || [];
			// empty array if not already initialized
			_jsH.filters[tag][priority] = _jsH.filters[tag][priority] || [];

			// add callback at the right place in ds
			// with respect to tag and priority
			_jsH.filters[tag][priority].push(callback);
		}
	};

	// object that contains functions that can
	// be used for removing callbacks from actions
	// and filters
	this.remove = {

		action : function(tag, callback) {
			// empty array if not already initialized
			_jsH.actions[tag] = _jsH.actions[tag] || [];

			// looping over all the priorities for the specified tag
			_jsH.actions[tag].forEach(function(priority, i) {
				// looping over all the callback
				priority.forEach(function(_callback, j) {
					// checking callback to remove
					if (_callback === callback) {
						// removing callback from ds
						_jsH.actions[tag][i].splice(j, 1);
					}
				});
			});
		},
		filter : function(tag, callback) {
			// empty array if not already initialized
			_jsH.filters[tag] = _jsH.filters[tag] || [];

			// looping over all the priorities for the specified tag
			_jsH.filters[tag].forEach(function(priority, i) {
				// looping over all the callback
				priority.forEach(function(_callback, j) {
					// checking callback to remove
					if (_callback === callback) {
						// removing callback from ds
						_jsH.filters[tag][i].splice(j, 1);
					}
				});
			});
		}
	};

	// object that contains functions that can
	// be used for applying or processing callbacks
	// from actions and filters
	this.process = {

		action : function(tag, options) {
			// check if tag is valid
			if (typeof _jsH.actions[tag] !== "undefined"
					&& _jsH.actions[tag].length > 0) {

				// looping over all priorities
				_jsH.actions[tag].forEach(function(priorities) {
					// looping over all callbacks
					priorities.forEach(function(callback) {
						// check if callback is a valid function
						if (typeof callback === "function") {
							callback(options); // call the callback
						}
					});
				});
			}
		},

		filter : function(tag, value, options) {
			// check if tag is valid
			if (typeof _jsH.filters[tag] !== "undefined"
					&& _jsH.filters[tag].length > 0) {

				// looping over all priorities
				_jsH.filters[tag].forEach(function(priorities) {
					// looping over all callbacks
					priorities.forEach(function(callback) {
						// check if callback is a valid function
						if (typeof callback === "function") {
							// callback should return a value
							// call the callback and save value
							value = callback(value, options);
						}
					});
				});
			}

			// return final value after being
			// processed by all the callback
			return value;
		}
	};
}

// this needs to be defined very early in the code
var _hooks;

// returns singleton _jsHooks object
function hooks() {
	if (typeof _hooks === 'undefined') {
		_hooks = new _jsHooks();
	}
	return _hooks;
}

// wrapper for adding filter
function add_filter(tag, callback, priority) {
	var _h = hooks();
	_h.add.filter(tag, callback, priority);
}

// wrapper for applying all the filters
function apply_filters(tag, value, options) {
	var _h = hooks();
	return _h.process.filter(tag, value, options);
}

// wrapper for removing filter with a certain callback
function remove_filter(tag, callback) {
	var _h = hooks();
	_h.remove.filter(tag, callback);
}

// --------------------------------------------------------------------------------------------------------------------------------
// EXAMPLE
// -------------------------------------------------------------------------------------------------------------------------------

function appendSalutation(name) {
	console.log('[Appending Salutation] Name: ' + name);
	return 'Hello ' + name + '!';
}
var name = "Rahul";
console.log("Original Name: " + name);

// FILTER 1
add_filter('name_changer', function(name) {
	console.log('[Appending Last Name] Name: ' + name);
	return name + ' Dhar';
});

// FILTER 2
add_filter('name_changer', appendSalutation);

// PROCESSED
console.log("After Filter: " + apply_filters('name_changer', name));

// RESULT
/**
 * Original Name: Rahul
 * [Appending Last Name] Name: Rahul
 * [Appending Salutation] Name: Rahul Dhar
 * After Filter: Hello Rahul Dhar!
 */