/**
Container that handles addition / deletion of arbitrary items.

An item is any object that has a `getFieldValues()` method,
which should return a JSON-serializable representation
of the item.

Containers copy "template" elements to create new items.
For example, to create a container for an item called "test_item",
the DOM should look something like:
    <div id="test_container" />
    <div id="test_item_template">
        <div class="test_item">
            <div class="test_item_remove_button">Remove</div>
            <p>This is the default value for the item.</p>
        </div>
    </div>
    <div id="test_item_add_button">Add</div>

A critical property of this setup is that the element you want to
include/duplicate is wrapped inside of a template element which is
the one that your reference when referring to a template. In the
above example, $("#test_item_template") would be the appropriate
reference to the template.

You can then initialize the container:
>>> var container = $("#test_container").get(0);
>>> var template = $("#test_item_template").get(0);
>>> var addButton = $("#test_item_add_button").get(0);
>>>
>>> container = OpenAssessment.Container(
>>>     ContainerItem, {
>>>         containerElement: container,
>>>         templateElement: template,
>>>         addButtonElement: addButton,
>>>         removeButtonClass: "test_item_remove_button"
>>>         containerItemClass: "test_item"
>>>     }
>>> );

The container is responsible for initializing the "add" and "remove" buttons,
including for pre-existing items in the container element.

Templates elements are never deleted, so they should be hidden using CSS styles.

Args:
    containerItem (constructor): The constructor of the container item object
        used to access the contents of items in the container.

Kwargs:
    containerElement (DOM element): The element representing the container.
    templateElement (DOM element):  The element containing the template for creating new items.
    addButtonElement (DOM element): The element of the button used to add new items to the container.
    removeButtonClass (string): The CSS class of the button that removes an item from the container.
        There may be one of these for each item in the container.
    containerItemClass (string): The CSS class of items in the container.
        New items will be assigned this class.
    notifier (OpenAssessment.Notifier): Used to send notifications of updates to container items.

**/
OpenAssessment.Container = function(containerItem, kwargs) {
    this.containerElement = kwargs.containerElement;
    this.templateElement = kwargs.templateElement;
    this.addButtonElement = kwargs.addButtonElement;
    this.removeButtonClass = kwargs.removeButtonClass;
    this.containerItemClass = kwargs.containerItemClass;
    this.notifier = kwargs.notifier;

    // Since every container item should be instantiated with
    // the notifier we were given, create a helper method
    // that does this automatically.
    var container = this;
    this.createContainerItem = function(element) {
        return new containerItem(element, container.notifier);
    };
};

OpenAssessment.Container.prototype = {

    /**
     Adds event listeners to the container and its children. Must be
     called explicitly when the container is initially created.
     */
    addEventListeners: function() {
        var container = this;
        // Install a click handler for the add button
        $(this.addButtonElement).click($.proxy(this.add, this));

        // Find items already in the container and install click
        // handlers for the delete buttons.
        $("." + this.removeButtonClass, this.containerElement).click(
            function(eventData) {
                var item = container.createContainerItem(eventData.target);
                container.remove(item);
            }
        );

        // Initialize existing items, in case they need to install their
        // own event handlers.
        $("." + this.containerItemClass, this.containerElement).each(
            function(index, element) {
                var item = container.createContainerItem(element);
                item.addEventListeners();
            }
        );
    },

    /**
    Adds a new item to the container.
    **/
    add: function() {
        // Copy the template into the container
        // Remove any CSS IDs (since now the element is not unique)
        // and add the item class so we can find it later.
        // Note that the element we add is the first child of the template element.
        // For more on the template structure expected, see the class comment
        $(this.templateElement)
            .children().first()
            .clone()
            .removeAttr('id')
            .toggleClass('is--hidden', false)
            .toggleClass(this.containerItemClass, true)
            .appendTo($(this.containerElement));

        // Install a click handler for the delete button
        // Since we just added the new element to the container,
        // it should be the last one.
        var container = this;
        var containerItem = $("." + this.containerItemClass, this.containerElement).last();
        containerItem.find('.' + this.removeButtonClass)
            .click(function(eventData) {
                var containerItem = container.createContainerItem(eventData.target);
                container.remove(containerItem);
            } );

        // Initialize the item, allowing it to install event handlers.
        // Fire event handler for adding a new element
        var handlerItem = container.createContainerItem(containerItem);
        handlerItem.addEventListeners();
        handlerItem.addHandler();
    },

    /**
    Remove the item associated with an element.
    If the element is not itself an item, traverse up the
    DOM tree until an item is found.

    Args:
        item: The container item object to remove.

    **/
    remove: function(item) {
        var itemElement = $(item.element).closest("." + this.containerItemClass);
        var containerItem = this.createContainerItem(itemElement);
        containerItem.removeHandler();
        itemElement.remove();
    },

    /**
    Retrieves the values that each container defines for itself, in the order in which they are
    presented in the DOM.

    Returns:
        array: The values representing each container item.

    **/
    getItemValues: function () {
        var values = [];
        var container = this;

        $("." + this.containerItemClass, this.containerElement).each(
            function(index, element) {
                var containerItem = container.createContainerItem(element);
                var fieldValues = containerItem.getFieldValues();
                values.push(fieldValues);
            }
        );

        return values;
    },

    /**
    Retrieve the element representing an item in this container.

    Args:
        index (int): The index of the item, starting from 0.

    Returns:
        Container item object or null.

    **/
    getItem: function(index) {
        var element = $("." + this.containerItemClass, this.containerElement).get(index);
        return (element !== undefined) ? this.createContainerItem(element) : null;
    },

    /**
    Retrieve all elements representing items in this container.

    Returns:
        array of container item objects

    **/
    getAllItems: function() {
        var container = this;
        return $("." + this.containerItemClass, this.containerElement)
            .map(function() { return container.createContainerItem(this); });
    }
};
