/**
 * FILE:settings.js
 * @short_description: File providing settings objects for xlets.
 *
 * This file provides the settings API for applets, desklets and extensions.
 */

const Gio = imports.gi.Gio;
const GLib = imports.gi.GLib;
const Lang = imports.lang;
const Cinnamon = imports.gi.Cinnamon;
const Main = imports.ui.main;
const Signals = imports.signals;
const Extension = imports.ui.extension;

/**
 * ENUM:BindingDirection
 * @IN: Set the property at binding time, and automatically update the property
 * and execute the callback when the setting file changes.  This is probably
 * the most common mode.
 *
 * @OUT: Set the property at binding time, and automatically update the setting
 * file when the property changes.  The callback can be omitted when using this
 * mode, as it will not be used.
 *
 * @BIDIRECTIONAL: Combines the effects of `IN` and `OUT`.
 *
 * The direction of binding settings
 *
 * Deprecated since 3.2: Binding direction is no longer meaningful. Please do not
 * use in new code.
 */
var BindingDirection = {
    IN : 1,
    OUT : 2,
    BIDIRECTIONAL : 3
};

var SETTINGS_TYPES = {
    "checkbox" : {
        "required-fields": [
            "type",
            "default",
            "description"
        ]
    },
    "switch" : {
        "required-fields": [
            "type",
            "default",
            "description"
        ]
    },
    "entry" : {
        "required-fields": [
            "type",
            "default",
            "description"
        ]
    },
    "textview" : {
        "required-fields": [
            "type",
            "default",
            "description"
        ]
    },
    "colorchooser" : {
        "required-fields": [
            "type",
            "default",
            "description"
        ]
    },
    "radiogroup" : {
        "required-fields": [
            "type",
            "default",
            "description",
            "options"
        ]
    },
    "filechooser" : {
        "required-fields": [
            "type",
            "description",
            "default"
        ]
    },
    "iconfilechooser" : {
        "required-fields": [
            "type",
            "description",
            "default"
        ]
    },
    "soundfilechooser" : {
        "required-fields": [
            "type",
            "description",
            "default"
        ]
    },
    "fontchooser" : {
        "required-fields": [
            "type",
            "description",
            "default"
        ]
    },
    "combobox" : {
        "required-fields": [
            "type",
            "default",
            "description",
            "options"
        ]
    },
    "tween" : {
        "required-fields": [
            "type",
            "default",
            "description"
        ]
    },
    "effect" : {
        "required-fields": [
            "type",
            "default",
            "description"
        ]
    },
    "keybinding" : {
        "required-fields": [
            "type",
            "default",
            "description"
        ]
    },
    "spinbutton" : {
        "required-fields": [
            "type",
            "default",
            "min",
            "max",
            "step",
            "description"
        ]
    },
    "scale" : {
        "required-fields": [
            "type",
            "default",
            "min",
            "max",
            "step",
            "description"
        ]
    },
    "generic" : {
        "required-fields": [
            "type",
            "default"
        ]
    },
    "datechooser" : {
        "required-fields": [
            "type",
            "default",
            "description"
        ]
    },
    "timechooser" : {
        "required-fields": [
            "type",
            "default",
            "description"
        ]
    },
    "list" : {
        "required-fields": [
            "type",
            "default",
            "columns"
        ]
    }
};

var NON_SETTING_TYPES = {
    "header" : {
        "required-fields": [
            "type",
            "description"
        ]
    },
    "separator" : {
        "required-fields": [
            "type"
        ]
    },
    "button" : {
        "required-fields": [
            "type",
            "description",
            "callback"
        ]
    },
    "label" : {
        "required-fields": [
            "type",
            "description"
        ]
    }
};

function settings_not_initialized_error(uuid) {
    global.logError("Could not set up binding - settings object was not initialized successfully for " + uuid);
}

function key_not_found_error (key_name, uuid) {
    global.logError("Could not find setting key '" + key_name + "' for xlet " + uuid);
}

function invalidKeyValueError (key_name, uuid) {
    global.logError(`Setting key ${key_name} for xlet ${uuid} is undefined or null`);
}

function invalid_setting_type_error (key_name, uuid, type) {
    global.logError("Invalid setting type '" + type + "' for setting key '" + key_name + "' of xlet " + uuid);
}

function options_not_supported_error(key_name, uuid, type) {
    global.logError("Invalid request for key '" + key_name + "' of xlet '" + uuid + "': type '" + type + "' doesn't support options");
}

function binding_not_found_error(key_name, uuid) {
    global.logError("could not unbind " + key_name + " for " + uuid + ": the binding does not exist");
}

function has_required_fields(props, key) {
    let type = props.type;
    let typeDef;

    if (type in SETTINGS_TYPES) typeDef = SETTINGS_TYPES[type];
    else if (type in NON_SETTING_TYPES) typeDef = NON_SETTING_TYPES[type];
    else return true;

    for (let field of typeDef["required-fields"]) {
        if (!(field in props)) {
            global.logError("Settings key " + key + " is missing property " + field);
            return false;
        }
    }

    return true;
}

function XletSettingsBase(bindObject, uuid, instanceId) {
    this._init(bindObject, uuid, instanceId);
}

/**
 * #XletSettingsBase:
 * @short_description: Object for handling xlet settings updates
 *
 * This object provides methods for binding settings to object properties, connecting
 * to signal change events, and getting and setting values. This class should not be
 * directly, but rather through one of the wrapper classes (#AppletSettings,
 * #DeskletSettings, or #ExtensionSettings)
 */
XletSettingsBase.prototype = {
    _init: function(bindObject, uuid, instanceId) {
        this.isReady = false;
        this.bindObject = bindObject;
        this.uuid = uuid;
        if (this._get_is_multi_instance_xlet(this.uuid)) this.instanceId = instanceId;
        else this.instanceId = this.uuid;
        this.bindings = {};

        if (!this._ensureSettingsFiles()) return;

        Main.settingsManager.register(this.uuid, this.instanceId, this);

        this.isReady = true;
    },

    /**
     * bindWithObject:
     * @bindObject (object): (optional) the object to which the setting will be bound
     * or null to use the bindObject passed to %_init
     * @key (string): the id of the setting
     * @applet_prop (string): the variable name that is used to hold the
     * setting (eg. `this.value` passes as `"value`")
     * @callback (function): (optional) the function to call when the setting changes
     * @user_data: (optional) any extra data/object you wish to pass to the callback
     *
     * Like bind this allows you to bind a setting to a property on an object. But unlike
     * %bind, this function allows you to specify the bindObject to which the property will
     * be bound.
     *
     * Returns (boolean): Whether the bind was successful
     */
    bindWithObject: function(bindObject, key, applet_prop, callback, user_data) {
        if (!this.isReady) {
            settings_not_initialized_error(this.uuid);
            return false;
        }
        if (!(key in this.settingsData)){
            key_not_found_error(key, this.uuid);
            return false;
        }
        if (this.settingsData[key] == null) {
            invalidKeyValueError(key, this.uuid);
            return false;
        }
        if (!(this.settingsData[key].type in SETTINGS_TYPES)) {
            invalid_setting_type_error(key, this.uuid, this.settingsData[key].type);
            return false;
        }

        let info = {propertyName: applet_prop, data: user_data, bindObject: bindObject};
        if (callback) info.callback = Lang.bind(bindObject, callback, user_data);

        let propDef = {
            get: Lang.bind(this, this._getValue, key),
            set: Lang.bind(this, this._setValue, key),
            enumerable: true,
            configurable: true
        }
        Object.defineProperty(bindObject, applet_prop, propDef);

        if ( !this.bindings[key] ) this.bindings[key] = [];
        this.bindings[key].push(info);

        // add a save function for objects or arrays
        if (this.settingsData[key].value != null
            && typeof(this.settingsData[key].value) === "object" && !this.settingsData[key].value.save) {
            info.isObject = true;
            this.settingsData[key].value.save = Lang.bind(this, this._saveToFile);
        }
        return true;
    },

    /**
     * bind:
     * @key (string): the id of the setting
     * @applet_prop (string): the variable name that is used to hold the
     * setting (eg. `this.value` passes as `"value`")
     * @callback (function): (optional) the function to call when the setting changes
     * @user_data: (optional) any extra data/object you wish to pass to the callback
     *
     * Bind a setting to a property on the @bindObject passed to %_init.
     *
     * Returns (boolean): Whether the bind was successful
     */
    bind: function(key, applet_prop, callback, user_data) {
        return this.bindWithObject(this.bindObject, key, applet_prop, callback, user_data)
    },

    /**
     * bindProperty:
     * @direction (Settings.BindingDirection): the direction of the binding
     * @key (string): the id of the setting
     * @applet_prop (string): the variable name that is used to hold the
     * setting (eg. `this.value` passes as `"value`")
     * @callback (function): (optional) the function to call when the setting changes
     * @user_data: (optional) any extra data/object you wish to pass to the callback
     *
     * Bind a setting to a property on the object @bindObject passed to %_init. This
     * function is deprecaed and is now only a wrapper around %bind for backward
     * compatibility. Please use %bind instead.
     *
     * Returns (boolean): Whether the bind was successful
     */
    bindProperty: function(direction, key, applet_prop, callback, user_data) {
        return this.bind(key, applet_prop, callback, user_data);
    },

    /**
     * unbindWithObject:
     * @bindObject (object): (optional) the object from which the setting will be unbound
     * @key (string): the previously bound key to remove
     *
     * Removes the binding on an object. If you have bound @key to multiple objects, this will
     * only remove the one bound to @bindObject. If you wish to remove all bindings, or you used
     * %bind or %bindProperty to bind the setting, it is recommended that you use %unbindPropery
     * instead.
     *
     * Returns (boolean): Whether the unbind was successful.
     */
    unbindWithObject: function(bindObject, key) {
        if ((key in this.bindings)) {
            for (let i in this.bindings[key]) {
                let info = this.bindings[key][i];
                if (info.bindObject != bindObject) continue;
                delete bindObject[info.propertyName];
                this.bindings[key].splice(i, 1);
                return true;
            }
        }

        binding_not_found_error(key, this.uuid);
        return false;
    },

    /**
     * unbind:
     * @key (string): the previously bound key to remove
     *
     * Removes the binding on an object that was bound using the %bind function. If you have bound
     * @key to multiple objects using %bindWithObject, you should use %unbindWithObject or %unbindAll
     * instead.
     *
     * Returns (boolean): Whether the unbind was successful.
     */
    unbind: function(key) {
        if ((key in this.bindings)) {
            for (let i in this.bindings[key]) {
                let info = this.bindings[key][i];
                if (info.bindObject != this.bindObject) continue;
                delete this.bindObject[info.propertyName];
                this.bindings[key].splice(i, 1);
                return true;
            }
        }

        binding_not_found_error(key, this.uuid);
        return false;
    },

    /**
     * unbindProperty:
     * @key (string): the previously bound key to remove
     *
     * Removes the binding of a key that was bound using %bind, or %bindProperty. This
     * function is deprecaed and is now only a wrapper around %unbind for backward
     * compatibility. Please use %unbind instead.
     *
     * Returns (boolean): Whether the unbind was successful.
     */
    unbindProperty: function (key) {
        this.unbind(key);
    },

    /**
     * unbindAll:
     * @key (string): the previously bound key to remove
     *
     * Removes all bindings of a key that were bound using %bind, %bindWithObject, or %bindProperty.
     *
     * Returns (boolean): Whether the unbind was successful.
     */
    unbindAll: function (key) {
        if (!(key in this.bindings)) {
            binding_not_found_error(key, this.uuid);
            return false;
        }

        for (let info of this.bindings[key]) {
            let bindObject = (info.bindObject) ? info.bindObject : this.bindObject;
            delete bindObject[info.propertyName];
        }
        delete this.bindings[key];
        return true;
    },

    _getValue: function(key) {
        let value = this.settingsData[key].value;

        if (value === undefined) {
            global.logWarning(`No value field in setting '${key}' for ${this.uuid}. Using default value.`);

            value = this.settingsData[key].default;
        }

        return value;
    },

    _setValue: function(value, key) {
        if (this.settingsData[key].value != value || typeof(value) == "object") {
            this.settingsData[key].value = value;
            this._saveToFile();
        }
    },

    /**
     * getValue:
     * @key (string): the name of the settings key
     *
     * Gets the value of the setting @key.
     *
     * Returns: The current value of the setting
     */
    getValue: function(key) {
        if (key in this.settingsData) return this._getValue(key);
        else {
            key_not_found_error(key, this.uuid);
            return null;
        }
    },

    /**
     * setValue:
     * @key (string): the name of the settings key
     * @value: the new value
     *
     * Sets the value of the setting @key to @value.
     */
    setValue: function(key, value) {
        if (!(key in this.settingsData)) {
            key_not_found_error(key, this.uuid);
            return;
        }
        this._setValue(value, key);
    },

    /**
     * getDefaultValue:
     * @key (string): the name of the settings key
     *
     * Gets the default value of the setting @key.
     *
     * Returns: The default value of the setting
     */
    getDefaultValue: function(key) {
        if (key in this.settingsData) {
            return this.settingsData[key].default;
        } else {
            key_not_found_error(key, this.uuid);
            return null;
        }
    },

    /**
     * getOptions:
     * @key (String): the name of the settings key
     *
     * Gets the current available options for the setting @key.
     *
     * Returns: The currently stored options of the key (or undefined if the key does
     * not support options)
     */
    getOptions: function (key) {
        if (!(key in this.settingsData)) {
            key_not_found_error(key, this.uuid);
            return null;
        }

        if (!("options" in this.settingsData[key])) {
            options_not_supported_error(key, this.uuid, this.settingsData[key].type);
            return null;
        }

        return this.settingsData[key].options;
    },

    /**
     * setOptions:
     * @key (string): the name of the settings key
     * @options: the new options to set
     *
     * Sets the available options of @key to @options. An error is given if the setting
     * does not support options.
     */
    setOptions: function (key, options) {
        if (!(key in this.settingsData)) {
            key_not_found_error(key, this.uuid);
            return;
        }

        if (!("options" in this.settingsData[key])) {
            options_not_supported_error(key, this.uuid, this.settingsData[key].type);
            return;
        }

        if (this.settingsData[key].options != options) {
            this.settingsData[key].options = options;
            this._saveToFile();
        }
    },


    /**
     * _checkSettings:
     *
     * Checks whether any settings have been changed and handles callbacks/signals if they have.
     */
    _checkSettings: function() {
        let oldSettings = this.settingsData;
        try {
            this.settingsData = this._loadFromFile();
        } catch(e) {
            global.logError(e);
            return;
        }

        let changed = false;
        for (let key in this.settingsData) {
            if (!this.settingsData[key]
                || this.settingsData[key].value === undefined
                || this.settingsData[key].type === undefined
                || !oldSettings[key]
                || oldSettings[key].value === undefined) continue;

            let oldValue = oldSettings[key].value;
            let value = this.settingsData[key].value;
            let valueType = this.settingsData[key].type;

            if (!this._hasSettingChanged(value, valueType, oldValue)) continue;
            
            changed = true;

            if (key in this.bindings) {
                for (let info of this.bindings[key]) {
                    // if the property had a save function, it is gone now and we need to re-add it
                    if (info.isObject && !this.settingsData[key].value.save) {
                        this.settingsData[key].value.save = Lang.bind(this, this._saveToFile);
                    }

                    if (info.callback) info.callback(value);
                }
            }

            /**
             * SIGNAL: changed::'key'
             * @key (string): The settings key who's value changed
             * @oldValue: The value of the key before the setting changed
             * @newValue: The value of the key after the setting changed
             *
             * Emitted when the value of the setting changes
             */
            this.emit("changed::" + key, key, oldValue, value);
        }

        /**
         * SIGNAL: settings-changed
         *
         * Emitted when any of the settings changes
         */
        if (changed) {
            this.emit("settings-changed");
        }
    },

    /**
     * _hasSettingChanged:
     * @value: current value
     * @valueType: current value setting type
     * @oldValue: previous value
     *
     * Checks whether a setting has changed by comparing is current value to the previous one
     */
    _hasSettingChanged: function(value, valueType, oldValue) {
        // It's easy to evaluate whether strings or ints changes, but
        // some settings are objects in such case every property needs to be checked 
        
        let equal = false;
        if (valueType === "timechooser" || valueType === "datechooser") {

            equal = Object.keys(value).every(
                key => oldValue.hasOwnProperty(key)
                && value[key] === oldValue[key]);

        } else if (valueType === "list") { 

            // If lists differ in length they definitely changed
            if (value.length !== oldValue.length) return true;

            // Each row of the list needs to be checked
            equal = Object.keys(value).every(row => {
                if (value[row].length === oldValue[row].length) {
                    return Object.keys(value[row]).every(
                        key => oldValue[row].hasOwnProperty(key)
                        && value[row][key] === oldValue[row][key]
                    );
                } else {
                    return false;
                }
            });    
              
        } else {
            equal = (value === oldValue);
        }
            
        return !equal;
    },

    _loadTemplate: function(checksum) {
        let xletDir = Extension.getExtension(this.uuid).dir;
        let templateFile = xletDir.get_child("settings-schema.json");
        let overrideFile = xletDir.get_child("settings-override.json");
        let overrideString, templateData;

        if (!templateFile.query_exists(null)) {
            throw "Unable to load template file for " + this.uuid + ": settings-schema.json could not be found";
        }

        let templateString = Cinnamon.get_file_contents_utf8_sync(templateFile.get_path());
        let newChecksum = global.get_md5_for_string(templateString);

        if (overrideFile.query_exists(null)) {
            overrideString = Cinnamon.get_file_contents_utf8_sync(overrideFile.get_path());
            newChecksum += global.get_md5_for_string(overrideString);
        }

        if (checksum && checksum == newChecksum) {
            return [false, null];
        }

        try {
            templateData = JSON.parse(templateString);
        } catch(e) {
            global.logError(e);
            throw "Failed to parse template file for " + this.uuid;
        }

        try {
            if (overrideString) {
                let overrideData = JSON.parse(overrideString);

                for (let key in overrideData) {
                    if ("override-props" in overrideData[key]) {
                        for (let prop in overrideData[key]) {
                            if (prop == "override-props") continue;
                            templateData[key][prop] = overrideData[key][prop];
                        }
                    }
                    else {
                        templateData[key] = overrideData[key];
                    }
                }
            }
        } catch(e) {
            global.logError("Settings override for " + this.uuid + "failed. Skipping for now.");
            global.logError(e);
        }

        templateData.__md5__ = newChecksum;

        return [true, templateData];
    },

    _ensureSettingsFiles: function() {
        let configPath = [GLib.get_user_config_dir(), "cinnamon", "spices", this.uuid].join("/");
        let configDir = Gio.file_new_for_path(configPath);
        if (!configDir.query_exists(null)) configDir.make_directory_with_parents(null);

        let configFile = configDir.get_child(this.instanceId + ".json")

        let oldConfigDir = Gio.file_new_for_path([GLib.get_home_dir(), ".cinnamon", "configs", this.uuid].join("/"));
        let oldConfigFile = oldConfigDir.get_child(this.instanceId + ".json");

        // We only use the config under the old path if it's the only one for backwards compatibility
        if (oldConfigFile.query_exists(null) && !configFile.query_exists(null))
            this.file = oldConfigFile;
        else 
            this.file = configFile;

        // If the settings have already been installed previously we need to check if the schema
        // has changed and if so, do an upgrade
        if (this.file.query_exists(null)) {
            try {
                this.settingsData = this._loadFromFile();
            } catch(e) {
                // Some users with a little bit of know-how may be able to fix the file if it's not too corrupted. Is it worth it to give an option to skip this step?
                global.logError(e);
                global.logError("Failed to parse file "+this.file.get_path()+". Attempting to rebuild the settings file for "+this.uuid+".");
            }
        }

        // if this.settingsData is populated, all we need to do is check for a newer version of the schema and upgrade if we find one
        // if not, it means either that an installation has not yet occurred, or something when wrong
        // either way, we need to install
        if (this.settingsData) {
            try {
                let [needsUpgrade, templateData] = this._loadTemplate(this.settingsData.__md5__);

                if (needsUpgrade) {
                    this._doUpgrade(templateData);
                    this._saveToFile();
                }
            } catch(e) {
                if (e) global.logError(e);
                global.logWarning("upgrade failed for " + this.uuid + ": falling back to previous settings");

                // if settings-schema.json is missing or corrupt, we just use the old version for now,
            }
        }
        else {
            // If the settings haven't already been installed, we need to do that now
            try {
                let [loaded, templateData] = this._loadTemplate();

                this._doInstall(templateData);
            } catch(e) {
                global.logError(e);
                global.logError("Unable to install settings for " + this.uuid);

                return false;
            }

            this._saveToFile();
        }

        return true;
    },

    _doInstall: function(templateData) {
        global.log("Installing settings for " + this.uuid);

        this.settingsData = templateData;
        for (let key in this.settingsData) {
            if (key == "__md5__") continue;

            let props = this.settingsData[key];

            // ignore anything that doesn't appear to be a valid settings type
            if (!("type" in props) || !("default" in props)) continue;

            if (!has_required_fields(props, key)) {
                throw "invalid settings for " + this.uuid;
            }

            if ('default' in props) {
                props.value = props.default;
            }
        }

        global.log("Settings successfully installed for " + this.uuid);
    },

    _doUpgrade: function(templateData) {
        global.log("Upgrading settings for " + this.uuid);

        for (let key in templateData) {
            if (key == "__md5__") continue;

            let props = templateData[key];

            // ignore anything that doesn't appear to be a valid settings type
            if (!("type" in props) || !("default" in props)) continue;

            if (!has_required_fields(props, key)) {
                throw "invalid settings for " + this.uuid;
            }

            // If the setting already exists, we want to use the old value. If not we use the default.
            let oldValue = null;
            if (this.settingsData[key] && this.settingsData[key].value !== undefined) {
                oldValue = this.settingsData[key].value;
                if (key in this.settingsData && this._checkSanity(oldValue, templateData[key])) templateData[key].value = oldValue;
            }
            if (!("value" in templateData[key])) templateData[key].value = templateData[key].default;
        }

        this.settingsData = templateData;
        global.log("Settings successfully upgraded for " + this.uuid);
    },

    _checkSanity: function(val, setting) {
        let found;
        switch (setting["type"]) {
            case "spinbutton":
            case "scale":
                return (val < setting["max"] && val > setting["min"]);
                break;
            case "combobox":
            case "radiogroup":
                found = false;
                for (let opt in setting["options"]) {
                    if (val == setting["options"][opt]) {
                        found = true;
                        break;
                    }
                }
                return found;
                break;
            default:
                return true;
                break;
        }
        return true;
    },

    _loadFromFile: function() {
        let rawData = Cinnamon.get_file_contents_utf8_sync(this.file.get_path());
        let json = JSON.parse(rawData);

        return json;
    },

    _saveToFile: function() {
        let rawData = JSON.stringify(this.settingsData, null, 4);
        let raw = this.file.replace(null, false, Gio.FileCreateFlags.NONE, null);
        let out_file = Gio.BufferedOutputStream.new_sized(raw, 4096);
        Cinnamon.write_string_to_stream(out_file, rawData);
        out_file.close(null);
    },

    // Called by cinnamonDBus.js when a setting is changed remotely in order to trigger
    // setting callbacks.
    remoteUpdate: function(key, payload) {
        this._checkSettings();
    },

    /**
     * finalize:
     *
     * Removes all bindings and disconnects all signals. This function should be called prior
     * to deleting the object.
     */
    finalize: function() {
        Main.settingsManager.unregister(this.uuid, this.instanceId);
        for (let key in this.bindings) {
            this.unbindAll(key);
        }
        this.disconnectAll();
    }
}
Signals.addSignalMethods(XletSettingsBase.prototype);

/**
 * #AppletSettings:
 * @short_description: Settings object for applets.
 *
 * Inherits: Settings.XletSettingsBase
 */
function AppletSettings(xlet, uuid, instanceId) {
    this._init(xlet, uuid, instanceId);
}

AppletSettings.prototype = {
    __proto__: XletSettingsBase.prototype,

    /**
     * _init:
     * @xlet (Object): the object variables are binded to (usually `this`)
     * @uuid (string): uuid of the applet
     * @instanceId (int): instance id of the applet
     */
    _init: function (xlet, uuid, instanceId) {
        XletSettingsBase.prototype._init.call(this, xlet, uuid, instanceId, "Applet");
    },

    _get_is_multi_instance_xlet: function(uuid) {
        return Extension.get_max_instances(uuid) != 1;
    },
};

/**
 * #DeskletSettings:
 * @short_description: Settings object for desklets.
 *
 * Inherits: Settings.XletSettingsBase
 */
function DeskletSettings(xlet, uuid, instanceId) {
    this._init(xlet, uuid, instanceId);
}

DeskletSettings.prototype = {
    __proto__: XletSettingsBase.prototype,

    /**
     * _init:
     * @xlet (Object): the object variables are binded to (usually `this`)
     * @uuid (string): uuid of the desklet
     * @instanceId (int): instance id of the desklet
     */
    _init: function (xlet, uuid, instanceId) {
        XletSettingsBase.prototype._init.call(this, xlet, uuid, instanceId, "Desklet");
    },

    _get_is_multi_instance_xlet: function(uuid) {
        return Extension.get_max_instances(uuid) > 1;
    }
};

/**
 * #ExtensionSettings:
 * @short_description: Settings object for extensions.
 *
 * Inherits: Settings.XletSettingsBase
 */
function ExtensionSettings(xlet, uuid) {
    this._init(xlet, uuid);
}

ExtensionSettings.prototype = {
    __proto__: XletSettingsBase.prototype,

    /**
     * _init:
     * @xlet (Object): the object variables are binded to (usually `this`)
     * @uuid (string): uuid of the extension
     */
    _init: function (xlet, uuid) {
        XletSettingsBase.prototype._init.call(this, xlet, uuid, null, "Extension");
    },

    _get_is_multi_instance_xlet: function(uuid) {
        return false;
    }
};

function SettingsManager() {
    this._init();
}

SettingsManager.prototype = {
    _init: function () {
        this.uuids = {};
    },

    register: function (uuid, instance_id, obj) {
        if (!(uuid in this.uuids))
            this.uuids[uuid] = {}
        this.uuids[uuid][instance_id] = obj;
    },

    unregister: function (uuid, instance_id) {
        this.uuids[uuid][instance_id] = null;
    }
};
