// Copyright (c) IPython Development Team.
// Distributed under the terms of the Modified BSD License.

define([
    "underscore",
    "backbone",
    "jquery",
    "base/js/utils",
    "base/js/namespace",
    "services/kernels/comm"
], function (_, Backbone, $, utils, IPython, comm) {
    "use strict";
    //--------------------------------------------------------------------
    // WidgetManager class
    //--------------------------------------------------------------------
    var WidgetManager = function (comm_manager, notebook) {
        /**
         * Public constructor
         */
        WidgetManager._managers.push(this);

        // Attach a comm manager to the 
        this.keyboard_manager = notebook.keyboard_manager;
        this.notebook = notebook;
        this.comm_manager = comm_manager;
        this.comm_target_name = 'ipython.widget';
        this._models = {}; /* Dictionary of model ids and model instance promises */

        // Register with the comm manager.
        this.comm_manager.register_target(this.comm_target_name, $.proxy(this._handle_comm_open, this));

        // Load the initial state of the widget manager if a load callback was
        // registered.
        var that = this;
        if (WidgetManager._load_callback) {
            Promise.resolve().then(function () {
                return WidgetManager._load_callback.call(that);
            }).then(function(state) {
                that.set_state(state);
            }).catch(utils.reject('Error loading widget manager state', true));
        }

        // Setup state saving code.
        this.notebook.events.on('before_save.Notebook', function() {
            var save_callback = WidgetManager._save_callback;
            var options = WidgetManager._get_state_options;
            if (save_callback) {
                that.get_state(options).then(function(state) {
                    save_callback.call(that, state);
                }).catch(utils.reject('Could not call widget save state callback.', true));
            }
        });
    };

    //--------------------------------------------------------------------
    // Class level
    //--------------------------------------------------------------------
    WidgetManager._model_types = {}; /* Dictionary of model type names (target_name) and model types. */
    WidgetManager._view_types = {}; /* Dictionary of view names and view types. */
    WidgetManager._managers = []; /* List of widget managers */
    WidgetManager._load_callback = null;
    WidgetManager._save_callback = null;

    WidgetManager.register_widget_model = function (model_name, model_type) {
        /** 
         * Registers a widget model by name.
         */
        WidgetManager._model_types[model_name] = model_type;
    };

    WidgetManager.register_widget_view = function (view_name, view_type) {
        /** 
         * Registers a widget view by name.
         */
        WidgetManager._view_types[view_name] = view_type;
    };

    WidgetManager.set_state_callbacks = function (load_callback, save_callback, options) {
        /**
         * Registers callbacks for widget state persistence.
         * 
         * Parameters
         * ----------
         * load_callback: function()
         *      function that is called when the widget manager state should be
         *      loaded.  This function should return a promise for the widget
         *      manager state.  An empty state is an empty dictionary `{}`.
         * save_callback: function(state as dictionary)
         *      function that is called when the notebook is saved or autosaved.
         *      The current state of the widget manager is passed in as the first
         *      argument.
         */
        WidgetManager._load_callback = load_callback;
        WidgetManager._save_callback = save_callback;
        WidgetManager._get_state_options = options;

        // Use the load callback to immediately load widget states.
        WidgetManager._managers.forEach(function(manager) {
            if (load_callback) {
                Promise.resolve().then(function () {
                    return load_callback.call(manager);
                }).then(function(state) {
                    manager.set_state(state);
                }).catch(utils.reject('Error loading widget manager state', true));
            }
        });
    };

    // Use local storage to persist widgets across page refresh by default.
    // LocalStorage is per domain, so we need to explicitly set the URL
    // that the widgets are associated with so they don't show on other 
    // pages hosted by the noteboook server.
    var url = [window.location.protocol, '//', window.location.host, window.location.pathname].join('');
    var key = 'widgets:' + url;
    WidgetManager.set_state_callbacks(function() {
        if (localStorage[key]) {
            return JSON.parse(localStorage[key]);
        }
        return {};
    }, function(state) {
        localStorage[key] = JSON.stringify(state);
    });

    //--------------------------------------------------------------------
    // Instance level
    //--------------------------------------------------------------------
    WidgetManager.prototype.display_view = function(msg, model) {
        /**
         * Displays a view for a particular model.
         */
        var cell = this.get_msg_cell(msg.parent_header.msg_id);
        if (cell === null) {
            return Promise.reject(new Error("Could not determine where the display" + 
                " message was from.  Widget will not be displayed"));
        } else {
            return this.display_view_in_cell(cell, model)
                .catch(utils.reject('Could not display view', true)); 
        }
    };

    WidgetManager.prototype.display_view_in_cell = function(cell, model) {
        // Displays a view in a cell.
        if (cell.display_widget_view) {
            var that = this;
            return cell.display_widget_view(this.create_view(model, {
                cell: cell,
                // Only set cell_index when view is displayed as directly.
                cell_index: that.notebook.find_cell_index(cell),
            })).then(function(view) {
                that._handle_display_view(view);
                view.trigger('displayed');
                return view;
            }).catch(utils.reject('Could not create or display view', true)); 
        } else {
            return Promise.reject(new Error('Cell does not have a `display_widget_view` method'));
        }
    };

    WidgetManager.prototype._handle_display_view = function (view) {
        /**
         * Have the IPython keyboard manager disable its event
         * handling so the widget can capture keyboard input.
         * Note, this is only done on the outer most widgets.
         */
        if (this.keyboard_manager) {
            this.keyboard_manager.register_events(view.$el);
        
            if (view.additional_elements) {
                for (var i = 0; i < view.additional_elements.length; i++) {
                    this.keyboard_manager.register_events(view.additional_elements[i]);
                }
            } 
        }
    };
    
    WidgetManager.prototype.create_view = function(model, options) {
        /**
         * Creates a promise for a view of a given model
         *
         * Make sure the view creation is not out of order with 
         * any state updates.
         */
        model.state_change = model.state_change.then(function() {
            
            return utils.load_class(model.get('_view_name'), model.get('_view_module'),
            WidgetManager._view_types).then(function(ViewType) {

                // If a view is passed into the method, use that view's cell as
                // the cell for the view that is created.
                options = options || {};
                if (options.parent !== undefined) {
                    options.cell = options.parent.options.cell;
                }
                // Create and render the view...
                var parameters = {model: model, options: options};
                var view = new ViewType(parameters);
                view.listenTo(model, 'destroy', view.remove);
                return Promise.resolve(view.render()).then(function() {return view;});
            }).catch(utils.reject("Couldn't create a view for model id '" + String(model.id) + "'", true));
        });
        var id = utils.uuid();
        model.views[id] = model.state_change;
        model.state_change.then(function(view) { 
            view.once('remove', function() {
                delete view.model.views[id];
            }, this);
        });
        return model.state_change;
    };

    WidgetManager.prototype.get_msg_cell = function (msg_id) {
        var cell = null;
        // First, check to see if the msg was triggered by cell execution.
        if (this.notebook) {
            cell = this.notebook.get_msg_cell(msg_id);
        }
        if (cell !== null) {
            return cell;
        }
        // Second, check to see if a get_cell callback was defined
        // for the message.  get_cell callbacks are registered for
        // widget messages, so this block is actually checking to see if the
        // message was triggered by a widget.
        var kernel = this.comm_manager.kernel;
        if (kernel) {
            var callbacks = kernel.get_callbacks_for_msg(msg_id);
            if (callbacks && callbacks.iopub &&
                callbacks.iopub.get_cell !== undefined) {
                return callbacks.iopub.get_cell();
            }
        }
        
        // Not triggered by a cell or widget (no get_cell callback 
        // exists).
        return null;
    };

    WidgetManager.prototype.callbacks = function (view) {
        /**
         * callback handlers specific a view
         */
        var callbacks = {};
        if (view && view.options.cell) {

            // Try to get output handlers
            var cell = view.options.cell;
            var handle_output = null;
            var handle_clear_output = null;
            if (cell.output_area) {
                handle_output = $.proxy(cell.output_area.handle_output, cell.output_area);
                handle_clear_output = $.proxy(cell.output_area.handle_clear_output, cell.output_area);
            }

            // Create callback dictionary using what is known
            var that = this;
            callbacks = {
                iopub : {
                    output : handle_output,
                    clear_output : handle_clear_output,

                    // Special function only registered by widget messages.
                    // Allows us to get the cell for a message so we know
                    // where to add widgets if the code requires it.
                    get_cell : function () {
                        return cell;
                    },
                },
            };
        }
        return callbacks;
    };

    WidgetManager.prototype.get_model = function (model_id) {
        /**
         * Get a promise for a model by model id.
         */
        return this._models[model_id];
    };

    WidgetManager.prototype._handle_comm_open = function (comm, msg) {
        /**
         * Handle when a comm is opened.
         */
        return this.create_model({
            model_name: msg.content.data.model_name, 
            model_module: msg.content.data.model_module, 
            comm: comm}).catch(utils.reject("Couldn't create a model.", true));
    };

    WidgetManager.prototype.create_model = function (options) {
        /**
         * Create and return a promise for a new widget model
         *
         * Minimally, one must provide the model_name and widget_class
         * parameters to create a model from Javascript.
         *
         * Example
         * --------
         * JS:
         * IPython.notebook.kernel.widget_manager.create_model({
         *      model_name: 'WidgetModel', 
         *      widget_class: 'IPython.html.widgets.widget_int.IntSlider'})
         *      .then(function(model) { console.log('Create success!', model); },
         *      $.proxy(console.error, console));
         *
         * Parameters
         * ----------
         * options: dictionary
         *  Dictionary of options with the following contents:
         *      model_name: string
         *          Target name of the widget model to create.
         *      model_module: (optional) string
         *          Module name of the widget model to create.
         *      widget_class: (optional) string
         *          Target name of the widget in the back-end.
         *      comm: (optional) Comm
         *
         * Create a comm if it wasn't provided.
         */
        var comm = options.comm;
        if (!comm) {
            comm = this.comm_manager.new_comm('ipython.widget', {'widget_class': options.widget_class});
        }

        var that = this;
        var model_id = comm.comm_id;
        var model_promise =  utils.load_class(options.model_name, options.model_module, WidgetManager._model_types)
            .then(function(ModelType) {
                var widget_model = new ModelType(that, model_id, comm);
                widget_model.once('comm:close', function () {
                    delete that._models[model_id];
                });
                widget_model.name = options.model_name;
                widget_model.module = options.model_module;
                return widget_model;

            }, function(error) {
                delete that._models[model_id];
                var wrapped_error = new utils.WrappedError("Couldn't create model", error);
                return Promise.reject(wrapped_error);
            });
        this._models[model_id] = model_promise;
        return model_promise;
    };

    WidgetManager.prototype.get_state = function(options) {
        /**
         * Asynchronously get the state of the widget manager.
         *
         * This includes all of the widget models and the cells that they are
         * displayed in.
         *
         * Parameters
         * ----------
         * options: dictionary
         *  Dictionary of options with the following contents:
         *      only_displayed: (optional) boolean=false
         *          Only return models with one or more displayed views.
         *      not_live: (optional) boolean=false
         *          Include models that have comms with severed connections.
         *
         * Returns
         * -------
         * Promise for a state dictionary
         */
        var that = this;
        return utils.resolve_promises_dict(this._models).then(function(models) {
            var state = {};

            var model_promises = [];
            for (var model_id in models) {
                if (models.hasOwnProperty(model_id)) {
                    var model = models[model_id];

                    // If the model has one or more views defined for it,
                    // consider it displayed.
                    var displayed_flag = !(options && options.only_displayed) || Object.keys(model.views).length > 0;
                    var live_flag = (options && options.not_live) || model.comm_live;
                    if (displayed_flag && live_flag) {
                        state[model_id] = {
                            model_name: model.name,
                            model_module: model.module,
                            state: model.get_state(),
                            views: [],
                        };

                        // Get the views that are displayed *now*.
                        (function(local_state) {
                            model_promises.push(utils.resolve_promises_dict(model.views).then(function(model_views) {
                                for (var id in model_views) {
                                    if (model_views.hasOwnProperty(id)) {
                                        var view = model_views[id];
                                        if (view.options.cell_index) {
                                            local_state.views.push(view.options.cell_index);
                                        }
                                    }
                                }
                            }));
                        })(state[model_id]);
                    }
                }
            }
            return Promise.all(model_promises).then(function() { return state; });
        }).catch(utils.reject('Could not get state of widget manager', true));
    };
    
    WidgetManager.prototype.set_state = function(state) {
        /**
         * Set the notebook's state.
         *
         * Reconstructs all of the widget models and attempts to redisplay the
         * widgets in the appropriate cells by cell index.
         */
        
        // Get the kernel when it's available.
        var that = this;
        return this._get_connected_kernel().then(function(kernel) {
            
            // Recreate all the widget models for the given state and 
            // display the views.
            that.all_views = [];
            var model_ids = Object.keys(state);
            for (var i = 0; i < model_ids.length; i++) {
                var model_id = model_ids[i];
                
                // Recreate a comm using the widget's model id (model_id == comm_id).
                var new_comm = new comm.Comm(kernel.widget_manager.comm_target_name, model_id);
                kernel.comm_manager.register_comm(new_comm);

                // Create the model using the recreated comm.  When the model is
                // created we don't know yet if the comm is valid so set_comm_live
                // false.  Once we receive the first state push from the back-end
                // we know the comm is alive.
                var views = kernel.widget_manager.create_model({
                    comm: new_comm, 
                    model_name: state[model_id].model_name, 
                    model_module: state[model_id].model_module})
                .then(function(model) {

                    model.set_comm_live(false);
                    var view_promise = Promise.resolve().then(function() {
                        return model.set_state(state[model.id].state);
                    }).then(function() {
                        model.request_state().then(function() {
                            model.set_comm_live(true);
                        });

                        // Display the views of the model.
                        var views = [];
                        var model_views = state[model.id].views;
                        for (var j=0; j<model_views.length; j++) {
                            var cell_index = model_views[j];
                            var cell = that.notebook.get_cell(cell_index);
                            views.push(that.display_view_in_cell(cell, model));
                        }
                        return Promise.all(views);
                    });
                    return view_promise;
                });
                that.all_views.push(views);
            }
            return Promise.all(that.all_views);
        }).catch(utils.reject('Could not set widget manager state.', true));  
    };

    WidgetManager.prototype._get_connected_kernel = function() {
        /**
         * Gets a promise for a connected kernel
         */
        var that = this;
        return new Promise(function(resolve, reject) {
            if (that.comm_manager && 
                that.comm_manager.kernel && 
                that.comm_manager.kernel.is_connected()) {

                resolve(that.comm_manager.kernel);
            } else {
                that.notebook.events.on('kernel_connected.Kernel', function(event, data) {
                    resolve(data.kernel);
                });
            }    
        });
    };

    // Backwards compatibility.
    IPython.WidgetManager = WidgetManager;

    return {'WidgetManager': WidgetManager};
});