define(function () {

	const DEFAULT_PLUGINS = [
		'settings/checkbox',
		'settings/textarea',
		'settings/select',
		'settings/array',
		'settings/key'
	];

	var Settings,
		onReady = [],
		waitingJobs = 0,
		helper;

	/*
	 * Attributes of HTML-tags that get used by default plugins:
	 *   + data-key:   the key to save/load the value within configuration-object
	 *   + data-type:  highest priority type-definition to determine what kind of element it is or which plugin to hook
	 *   + type:       normal priority type-definition
	 *   + data-empty: if 'false' or '0' then values that are assumed as empty turn into null. data-empty of arrays affect
	 *                 their child-elements
	 *   + data-trim:  if not 'false' or '0' then values will get trimmed as defined by the elements type
	 *   + data-split: if set and the element doesn't belong to any plugin, it's value will get split and joined by its
	 *                 value into the input-field
	 *   array-elements:
	 *     + data-split:      separator (HTML allowed) between the elements, defaults to ', '
	 *     + data-new:        value to insert into new created elements
	 *     + data-attributes: an object to set the attributes of the child HTML-elements. tagName as special key will set
	 *                        the tag-name of the child HTML-elements
	 *   key-fields:
	 *     + data-trim:  if 'false' or '0' then the value will get saved as string else as object providing following
	 *                   properties: ctrl, alt, shift, meta, code, char
	 *     + data-split: separator between different modifiers and the key-code of the value that gets saved
	 *                   (only takes effect if trimming)
	 *     + data-short: if not 'false' or '0' then modifier-keys get saved as first uppercase character
	 *                   (only takes effect if trimming)
	 *   select:
	 *     + data-options: an array of {"text":"Displayed Text","value":"some_value"}-like objects
	 *
	 * The name of the HTML-tag is lowest priority type-definition
	 *
	 * Examples-HTML:
	     No!
	     <input type="checkbox" data-key="cfg1"></input><br>
	     Yes!
	     <input type="checkbox" data-key="cfg2"></input><br>
	     An array of checkboxes that are selected by default:
	     <div data-key="cfg3" data-attributes='{"data-type":"checkbox"}' data-new='true'></div><br>
	     A simple input-field of any common type:
	     <input type="password" data-key="cfg4"></input><br>
	     A simple textarea:
	     <textarea data-key="cfg5"></textarea><br>
	     Array of textareas:
	     <div data-key="cfg6" data-attributes='{"data-type":"textarea"}' data-new='Hello Kitty, ahem... World!'></div><br>
	     2D-Array of numbers that persist even when empty (but not empty rows):
	     <div data-key="cfg7" data-split="<br>" data-attributes='{"data-type":"array","data-attributes":{"type":"number"}}' data-new='[42,21]'></div><br>
	     Same with persisting empty rows, but not empty numbers, if no row is given null will get saved:
	     <div data-key="cfg8" data-split="<br>" data-empty="false" data-attributes='{"data-type":"array","data-empty":true,"data-attributes":{"type":"number","data-empty":false}}' data-new='[42,21]'></div><br>
	     Array of Key-shortcuts (new: Ctrl+Shift+7):
	     <div data-key="cfg9" data-attributes='{"data-type":"key"}' data-new='Ctrl+Shift+#55'></div><br>
	     Array of numbers (new: 42, step: 21):
	     <div data-key="cfg10" data-attributes='{"data-type":"number","step":21}' data-new='42'></div><br>
	     Select with dynamic options:
	     <select data-key="cfg11" data-options='[{"value":"2","text":"2"},{"value":"3","text":"3"}]'></select><br>
	     Select that loads faster:
	     <select data-key="cfg12"><br>
	     <option value="2">2</option>
	     <option value="3">3</option>
	     </select>
	 *
	 * Matching configuration:
	     {
	       cfg1: false,
	       cfg2: true,
	       cfg3: [false, false, true],
	       cfg4: 'hello world',
	       cfg5: 'some\nlong\ntext',
	       cfg6: ['some\nlong\ntexts', 'and another one'],
	       cfg7: [[]],
	       cfg8: [[]],
	       cfg9: [],
	       cfg10: [],
	       cfg11: 3,
	       cfg12: 2
	     }
	 */

	/**
	 Returns the hook of given name that matches the given type or element.
	 @param type The type of the element to get the matching hook for, or the element itself.
	 @param name The name of the hook.
	 */
	function getHook(type, name) {
		var hook, plugin;
		if (typeof type !== 'string') {
			type = $(type);
			type = type.data('type') || type.attr('type') || type.prop('tagName');
		}
		plugin = Settings.plugins[type.toLowerCase()];
		if (plugin == null) {
			return void 0;
		}
		hook = plugin[name];
		if (typeof hook === 'function') {
			return hook;
		} else {
			return null;
		}
	}

	helper = {
		/**
		 @returns Object A deep clone of the given object.
		 */
		deepClone: function (obj) {
			if (typeof obj === 'object') {
				return JSON.parse(JSON.stringify(obj));
			} else {
				return obj;
			}
		},
		/**
		 Creates a new Element with given data.
		 @param tagName The tag-name of the element to create.
		 @param data The attributes to set.
		 @param text The text to add into the element.
		 @returns HTMLElement The created element.
		 */
		createElement: function (tagName, data, text) {
			var element = document.createElement(tagName);
			for (var k in data) {
				element.setAttribute(k, data[k]);
			}
			if (text) {
				element.appendChild(document.createTextNode(text));
			}
			return element;
		},
		/**
		 Calls the init-hook of the given element.
		 @param element The element to initialize.
		 */
		initElement: function (element) {
			var hook = getHook(element, 'init');
			if (hook != null) {
				hook.call(Settings, $(element));
			}
		},
		/**
		 Calls the destruct-hook of the given element.
		 @param element The element to destruct.
		 */
		destructElement: function (element) {
			var hook = getHook(element, 'destruct');
			if (hook != null) {
				hook.call(Settings, $(element));
			}
		},
		/**
		 Creates and initializes a new element.
		 @param type The type of the new element.
		 @param tagName The tag-name of the new element.
		 @param data The data to forward to create-hook or use as attributes.
		 @returns JQuery The created element.
		 */
		createElementOfType: function (type, tagName, data) {
			var element, hook = getHook(type, 'create');
			if (hook != null) {
				element = $(hook.call(Settings, type, tagName, data));
			} else {
				if (data == null) {
					data = {};
				}
				if (type != null) {
					data.type = type;
				}
				element = $(helper.createElement(tagName || 'input', data))
			}
			element.data('type', type);
			helper.initElement(element);
			return element;
		},
		/**
		 Creates a new Array that contains values of given Array depending on trim and empty.
		 @param array The array to clean.
		 @param trim Whether to trim each value if it has a trim-function.
		 @param empty Whether empty values should get added.
		 @returns Array The filtered and/or modified Array.
		 */
		cleanArray: function (array, trim, empty) {
			var cleaned = [];
			if (!trim && empty) {
				return array;
			}
			for (var i = 0; i < array.length; i++) {
				var value = array[i];
				if (trim) {
					value = value === true ? 1 : value === false ? 0 : typeof value.trim === 'function' ? value.trim() : value;
				}
				if (empty || (value != null ? value.length : void 0)) {
					cleaned.push(value);
				}
			}
			return cleaned;
		},
		isTrue: function (value) {
			return value === 'true' || +value === 1;
		},
		isFalse: function (value) {
			return value === 'false' || +value === 0;
		},
		/**
		 Calls the get-hook of the given element and returns its result.
		 If no hook is specified it gets treated as input-field.
		 @param element The element of that the value should get read.
		 @returns Object The value of the element.
		 */
		readValue: function (element) {
			var empty = !helper.isFalse(element.data('empty')),
				trim = !helper.isFalse(element.data('trim')),
				split = element.data('split'),
				hook = getHook(element, 'get'),
				value;
			if (hook != null) {
				return hook.call(Settings, element, trim, empty);
			}
			if (split != null) {
				empty = helper.isTrue(element.data('empty')); // default empty-value is false for arrays
				value = element.val();
				var array = (value != null ? value.split(split || ',') : void 0) || [];
				return helper.cleanArray(array, trim, empty);
			} else {
				value = element.val();
				if (trim && value != null && typeof value.trim === 'function') {
					value = value.trim();
				}
				if (empty || value !== void 0 && (value == null || value.length !== 0)) {
					return value;
				} else {
					return void 0;
				}
			}
		},
		/**
		 Calls the set-hook of the given element.
		 If no hook is specified it gets treated as input-field.
		 @param element The JQuery-Object of the element to fill.
		 @param value The value to set.
		 */
		fillField: function (element, value) {
			var hook = getHook(element, 'set'),
				trim = element.data('trim');
			trim = trim !== 'false' && +trim !== 0;
			if (hook != null) {
				return hook.call(Settings, element, value, trim);
			}
			if (value instanceof Array) {
				value = value.join(element.data('split') || (trim ? ', ' : ','));
			}
			if (trim && value && typeof value.trim === 'function') {
				value = value.trim();
				if (typeof value.toString === 'function') {
					value = value.toString();
				}
			} else if (value != null) {
				if (typeof value.toString === 'function') {
					value = value.toString();
				}
				if (trim) {
					value = value.trim();
				}
			} else {
				value = '';
			}
			if (value !== void 0) {
				element.val(value);
			}
		},
		/**
		 Calls the init-hook and {@link helper.fillField} on each field within wrapper-object.
		 @param wrapper The wrapper-element to set settings within.
		 */
		initFields: function (wrapper) {
			$('[data-key]', wrapper).each(function (ignored, field) {
				field = $(field);
				var hook = getHook(field, 'init'),
					keyParts = field.data('key').split('.'),
					value = Settings.get();
				if (hook != null) {
					hook.call(Settings, field);
				}
				for (var i = 0; i < keyParts.length; i++) {
					var part = keyParts[i];
					if (part && value != null) {
						value = value[part];
					}
				}
				helper.fillField(field, value);
			});
		},
		/**
		 Increases the amount of jobs before settings are ready by given amount.
		 @param amount The amount of jobs to register.
		 */
		registerReadyJobs: function (amount) {
			return waitingJobs += amount;
		},
		/**
		 Decreases the amount of jobs before settings are ready by given amount or 1.
		 If the amount is less or equal 0 all callbacks registered by {@link helper.whenReady} get called.
		 @param amount The amount of jobs that finished.
		 */
		beforeReadyJobsDecreased: function (amount) {
			if (amount == null) {
				amount = 1;
			}
			if (waitingJobs > 0) {
				waitingJobs -= amount;
				if (waitingJobs <= 0) {
					for (var i = 0; i < onReady.length; i++) {
						onReady[i]();
					}
					onReady = [];
				}
			}
		},
		/**
		 Calls the given callback when the settings are ready.
		 @param callback The callback.
		 */
		whenReady: function (callback) {
			if (waitingJobs <= 0) {
				callback();
			} else {
				onReady.push(callback);
			}
		},
		/**
		 Persists the given settings with given hash.
		 @param hash The hash to use as settings-id.
		 @param settings The settings-object to persist.
		 @param notify Whether to send notification when settings got saved.
		 @param callback The callback to call when done.
		 */
		persistSettings: function (hash, settings, notify, callback) {
			if (settings != null && settings._settings != null && typeof settings._settings !== 'string') {
				settings = helper.deepClone(settings);
				settings._settings = JSON.stringify(settings._settings);
			}
			socket.emit('admin.settings.set', {
				hash: hash,
				values: settings
			}, function (err) {
				if (notify) {
					if (err) {
						app.alert({
							title: 'Settings Not Saved',
							type: 'danger',
							message: "NodeBB failed to save the settings.",
							timeout: 5000
						});
						console.log('[settings] Unable to set settings for hash: ', hash);
					} else {
						app.alert({
							title: 'Settings Saved',
							type: 'success',
							timeout: 2500
						});
					}
				}
				if (typeof callback === 'function') {
					callback(err);
				}
			});
		},
		/**
		 Sets the settings to use to given settings.
		 @param settings The settings to use.
		 */
		use: function (settings) {
			try {
				settings._settings = JSON.parse(settings._settings);
			} catch (_error) {}
			Settings.cfg = settings;
		}
	};


	Settings = {
		helper: helper,
		plugins: {},
		cfg: {},

		/**
		 Returns the saved settings.
		 @returns Object The settings.
		 */
		get: function () {
			if (Settings.cfg != null && Settings.cfg._settings !== void 0) {
				return Settings.cfg._settings;
			}
			return Settings.cfg;
		},
		/**
		 Registers a new plugin and calls its use-hook.
		 A plugin is an object containing a types-property to define its default bindings.
		 A plugin may also provide the following properties of type function with [return-value] (parameters):
		 use [void] - gets called when the Settings initializes the plugin.
		 init [void] (element) - gets called on page-load and every time after the create-hook.
		 ; element: The element to initialize.
		 create [JQuery-Object] (type, tagName, data) - gets called when a new HTML-instance needs to get created.
		 ; type: A string that identifies the plugin itself within this Settings-instance if set as data-type.
		 ; tagName: The tag-name that gets requested.
		 ; data: Additional data, plugin-dependent meaning.
		 destruct [void] (element) - gets called after a HTML-instance got removed from DOM
		 ; element: The element that got removed.
		 set [void] (element, value, trim) - gets called when the value of the element should be set to the given value.
		 ; element: The element to set its value.
		 ; value: The value to set.
		 ; trim: Whether the value is considered as trimmed.
		 get [value] (element, trim, empty) - gets called when the value of the given instance is needed.
		 ; element: The element to get its value.
		 ; trim: Whether the result should be trimmed.
		 ; empty: Whether considered as empty values should get saved too.
		 All passed elements are JQuery-Objects.
		 @param service The plugin to register.
		 @param types The types to bind the plugin to.
		 */
		registerPlugin: function (service, types) {
			if (types == null) {
				types = service.types;
			} else {
				service.types = types;
			}
			if (typeof service.use === 'function') {
				service.use.call(Settings);
			}
			for (var i = 0; i < types.length; i++) {
				var type = types[i].toLowerCase();
				if (Settings.plugins[type] == null) {
					Settings.plugins[type] = service;
				}
			}
		},
		/**
		 Sets the settings to given ones, resets the fields within given wrapper and saves the settings server-side.
		 @param hash The hash to use as settings-id.
		 @param settings The settings to set.
		 @param wrapper The wrapper-element to find settings within.
		 @param callback The callback to call when done.
		 @param notify Whether to send notification when settings got saved.
		 */
		set: function (hash, settings, wrapper, callback, notify) {
			if (notify == null) {
				notify = true;
			}
			helper.whenReady(function () {
				helper.use(settings);
				helper.initFields(wrapper || 'form');
				helper.persistSettings(hash, settings, notify, callback);
			});
		},
		/**
		 Fetches the settings from server and calls {@link Settings.helper.initFields} once the settings are ready.
		 @param hash The hash to use as settings-id.
		 @param wrapper The wrapper-element to set settings within.
		 @param callback The callback to call when done.
		 */
		sync: function (hash, wrapper, callback) {
			socket.emit('admin.settings.get', {
				hash: hash
			}, function (err, values) {
				if (err) {
					console.log('[settings] Unable to load settings for hash: ', hash);
					if (typeof callback === 'function') {
						callback(err);
					}
				} else {
					helper.whenReady(function () {
						helper.use(values);
						helper.initFields(wrapper || 'form');
						if (typeof callback === 'function') {
							callback();
						}
					});
				}
			});
		},
		/**
		 Reads the settings from fields and saves them server-side.
		 @param hash The hash to use as settings-id.
		 @param wrapper The wrapper-element to find settings within.
		 @param callback The callback to call when done.
		 @param notify Whether to send notification when settings got saved.
		 */
		persist: function (hash, wrapper, callback, notify) {
			var notSaved = [],
				fields = $('[data-key]', wrapper || 'form').toArray();
			if (notify == null) {
				notify = true;
			}
			for (var i = 0; i < fields.length; i++) {
				var field = $(fields[i]),
					value = helper.readValue(field),
					parentCfg = Settings.get(),
					keyParts = field.data('key').split('.'),
					lastKey = keyParts[keyParts.length - 1];
				if (keyParts.length > 1) {
					for (var j = 0; j < keyParts.length - 1; j++) {
						var part = keyParts[j];
						if (part && parentCfg != null) {
							parentCfg = parentCfg[part];
						}
					}
				}
				if (parentCfg != null) {
					if (value != null) {
						parentCfg[lastKey] = value;
					} else {
						delete parentCfg[lastKey];
					}
				} else {
					notSaved.push(field.data('key'));
				}
			}
			if (notSaved.length) {
				app.alert({
					title: 'Attributes Not Saved',
					message: "'" + (notSaved.join(', ')) + "' could not be saved. Please contact the plugin-author!",
					type: 'danger',
					timeout: 5000
				});
			}
			helper.persistSettings(hash, Settings.cfg, notify, callback);
		},
		load: function(hash, formEl, callback) {
			socket.emit('admin.settings.get', {
				hash: hash
			}, function(err, values) {
				if (!err) {
					$(formEl).deserialize(values);
					if (typeof callback === 'function') {
						callback();
					}
				} else {
					console.log('[settings] Unable to load settings for hash: ', hash);
				}
			});
		},
		save: function(hash, formEl, callback) {
			formEl = $(formEl);
			if (formEl.length) {
				var	values = formEl.serializeObject();
				// "Fix" checkbox values, so that unchecked options are not omitted
				formEl.find('input[type="checkbox"]').each(function(idx, inputEl) {
					inputEl = $(inputEl);
					if (!inputEl.is(':checked')) {
						values[inputEl.attr('id')] = 'off';
					}
				});
				socket.emit('admin.settings.set', {
					hash: hash,
					values: values
				}, function(err) {
					app.alert({
						title: 'Settings Saved',
						type: 'success',
						timeout: 2500
					});
					if (typeof callback === 'function') {
						callback();
					}
				});
			} else {
				console.log('[settings] Form not found.');
			}
		}
	};


	helper.registerReadyJobs(1);
	require(DEFAULT_PLUGINS, function () {
		for (var i = 0; i < arguments.length; i++) {
			Settings.registerPlugin(arguments[i]);
		}
		helper.beforeReadyJobsDecreased();
	});

	return Settings;

});