Proyectos de Subversion Moodle

// This file is part of Moodle - http://moodle.org/

//

// Moodle is free software: you can redistribute it and/or modify

// it under the terms of the GNU General Public License as published by

// the Free Software Foundation, either version 3 of the License, or

// (at your option) any later version.

//

// Moodle is distributed in the hope that it will be useful,

// but WITHOUT ANY WARRANTY; without even the implied warranty of

// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

// GNU General Public License for more details.

//

// You should have received a copy of the GNU General Public License

// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.

/**

 * JavaScript to make drag-drop into text questions work.

 *

 * Some vocabulary to help understand this code:

 *

 * The question text contains 'drops' - blanks into which the 'drags', the missing

 * words, can be put.

 *

 * The thing that can be moved into the drops are called 'drags'. There may be

 * multiple copies of the 'same' drag which does not really cause problems.

 * Each drag has a 'choice' number which is the value set on the drop's hidden

 * input when this drag is placed in a drop.

 *

 * These may be in separate 'groups', distinguished by colour.

 * Things can only interact with other things in the same group.

 * The groups are numbered from 1.

 *

 * The place where a given drag started from is called its 'home'.

 *

 * @module     qtype_ddwtos/ddwtos

 * @copyright  2018 The Open University

 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later

 * @since      3.6

 */

define([

    'jquery',

    'core/dragdrop',

    'core/key_codes',

    'core_form/changechecker',

    'core_filters/events',

], function(

    $,

    dragDrop,

    keys,

    FormChangeChecker,

    filterEvent

) {

    "use strict";

    /**

     * Object to handle one drag-drop into text question.

     *

     * @param {String} containerId id of the outer div for this question.

     * @param {boolean} readOnly whether the question is being displayed read-only.

     * @constructor

     */

    function DragDropToTextQuestion(containerId, readOnly) {

        const thisQ = this;

        this.containerId = containerId;

        this.questionAnswer = {};

        this.questionDragDropWidthHeight = [];

        if (readOnly) {

            this.getRoot().addClass('qtype_ddwtos-readonly');

        }

        this.resizeAllDragsAndDrops();

        this.cloneDrags();

        this.positionDrags();

        // Wait for all dynamic content loaded by filter to be completed.

        document.addEventListener(filterEvent.eventTypes.filterContentRenderingComplete, (elements) => {

            elements.detail.nodes.forEach((element) => {

                thisQ.changeAllDragsAndDropsToFilteredContent(element);

            });

        });

    }

    /**

     * In each group, resize all the items to be the same size.

     */

    DragDropToTextQuestion.prototype.resizeAllDragsAndDrops = function() {

        var thisQ = this;

        this.getRoot().find('.answercontainer > div').each(function(i, node) {

            thisQ.resizeAllDragsAndDropsInGroup(

                thisQ.getClassnameNumericSuffix($(node), 'draggrouphomes'));

        });

    };

    /**

     * In a given group, set all the drags and drops to be the same size.

     *

     * @param {int} group the group number.

     */

    DragDropToTextQuestion.prototype.resizeAllDragsAndDropsInGroup = function(group) {

        var thisQ = this,

            dragDropItems = this.getRoot().find('span.group' + group),

            maxWidth = 0,

            maxHeight = 0;

        // Find the maximum size of any drag in this groups.

        dragDropItems.each(function(i, drag) {

            maxWidth = Math.max(maxWidth, Math.ceil(drag.offsetWidth));

            maxHeight = Math.max(maxHeight, Math.ceil(0 + drag.offsetHeight));

        });

        // The size we will want to set is a bit bigger than this.

        maxWidth += 8;

        maxHeight += 2;

        thisQ.questionDragDropWidthHeight[group] = {maxWidth: maxWidth, maxHeight: maxHeight};

        // Set each drag home to that size.

        dragDropItems.each(function(i, drag) {

            thisQ.setElementSize(drag, maxWidth, maxHeight);

        });

    };

    /**

     * Change all the drags and drops related to the item that has been changed by filter to correct size and content.

     *

     *  @param {object} filteredElement the element has been modified by filter.

     */

    DragDropToTextQuestion.prototype.changeAllDragsAndDropsToFilteredContent = function(filteredElement) {

        let currentFilteredItem = $(filteredElement);

        const parentIsDD = currentFilteredItem.parent().closest('span').hasClass('placed') ||

            currentFilteredItem.parent().closest('span').hasClass('draghome');

        const isDD = currentFilteredItem.hasClass('placed') || currentFilteredItem.hasClass('draghome');

        // The filtered element or parent element should a drag or drop item.

        if (!parentIsDD && !isDD) {

            return;

        }

        if (parentIsDD) {

            currentFilteredItem = currentFilteredItem.parent().closest('span');

        }

        const thisQ = this;

        if (thisQ.getRoot().find(currentFilteredItem).length <= 0) {

            // If the DD item doesn't belong to this question

            // In case we have multiple questions in the same page.

            return;

        }

        const group = thisQ.getGroup(currentFilteredItem),

              choice = thisQ.getChoice(currentFilteredItem);

        let listOfModifiedDragDrop = [];

        // Get the list of drag and drop item within the same group and choice.

        this.getRoot().find('.group' + group + '.choice' + choice).each(function(i, node) {

            // Same modified item, skip it.

            if ($(node).get(0) === currentFilteredItem.get(0)) {

                return;

            }

            const originalClass = $(node).attr('class');

            const originalStyle = $(node).attr('style');

            // We want to keep all the handler and event for filtered item, so using clone is the only choice.

            const filteredDragDropClone = currentFilteredItem.clone();

            // Replace the class and style of the drag drop item we want to replace for the clone.

            filteredDragDropClone.attr('class', originalClass);

            filteredDragDropClone.attr('style', originalStyle);

            // Insert into DOM.

            $(node).before(filteredDragDropClone);

            // Add the item has been replaced to a list so we can remove it later.

            listOfModifiedDragDrop.push(node);

        });

        listOfModifiedDragDrop.forEach(function(node) {

            $(node).remove();

        });

        // Save the current height and width.

        const currentHeight = currentFilteredItem.height();

        const currentWidth = currentFilteredItem.width();

        // Set to auto so we can get the real height and width of the filtered item.

        currentFilteredItem.height('auto');

        currentFilteredItem.width('auto');

        // We need to set display block so we can get height and width.

        // Some browser can't get the offsetWidth/Height if they are an inline element like span tag.

        if (!filteredElement.offsetWidth || !filteredElement.offsetHeight) {

            filteredElement.classList.add('d-block');

        }

        if (thisQ.questionDragDropWidthHeight[group].maxWidth < Math.ceil(filteredElement.offsetWidth) ||

            thisQ.questionDragDropWidthHeight[group].maxHeight < Math.ceil(0 + filteredElement.offsetHeight)) {

            // Remove the d-block class before calculation.

            filteredElement.classList.remove('d-block');

            // Now resize all the items in the same group if we have new maximum width or height.

            thisQ.resizeAllDragsAndDropsInGroup(group);

        } else {

            // Return the original height and width in case the real height and width is not the maximum.

            currentFilteredItem.height(currentHeight);

            currentFilteredItem.width(currentWidth);

        }

        // Remove the d-block class after resize.

        filteredElement.classList.remove('d-block');

    };

    /**

     * Set a given DOM element to be a particular size.

     *

     * @param {HTMLElement} element

     * @param {int} width

     * @param {int} height

     */

    DragDropToTextQuestion.prototype.setElementSize = function(element, width, height) {

        $(element).width(width).height(height).css('lineHeight', height + 'px');

    };

    /**

     * Invisible 'drag homes' are output by the renderer. These have the same properties

     * as the drag items but are invisible. We clone these invisible elements to make the

     * actual drag items.

     */

    DragDropToTextQuestion.prototype.cloneDrags = function() {

        var thisQ = this;

        thisQ.getRoot().find('span.draghome').each(function(index, draghome) {

            var drag = $(draghome);

            var placeHolder = drag.clone();

            placeHolder.removeClass();

            placeHolder.addClass('draghome choice' +

                thisQ.getChoice(drag) + ' group' +

                thisQ.getGroup(drag) + ' dragplaceholder');

            drag.before(placeHolder);

        });

    };

    /**

     * Update the position of drags.

     */

    DragDropToTextQuestion.prototype.positionDrags = function() {

        var thisQ = this,

            root = this.getRoot();

        // First move all items back home.

        root.find('span.draghome').not('.dragplaceholder').each(function(i, dragNode) {

            var drag = $(dragNode),

                currentPlace = thisQ.getClassnameNumericSuffix(drag, 'inplace');

            drag.addClass('unplaced')

                .removeClass('placed');

            drag.removeAttr('tabindex');

            if (currentPlace !== null) {

                drag.removeClass('inplace' + currentPlace);

            }

        });

        // Then place the once that should be placed.

        root.find('input.placeinput').each(function(i, inputNode) {

            var input = $(inputNode),

                choice = input.val(),

                place = thisQ.getPlace(input);

            // Record the last known position of the drop.

            var drop = root.find('.drop.place' + place),

                dropPosition = drop.offset();

            drop.data('prev-top', dropPosition.top).data('prev-left', dropPosition.left);

            if (choice === '0') {

                // No item in this place.

                return;

            }

            // Get the unplaced drag.

            var unplacedDrag = thisQ.getUnplacedChoice(thisQ.getGroup(input), choice);

            // Get the clone of the drag.

            var hiddenDrag = thisQ.getDragClone(unplacedDrag);

            if (hiddenDrag.length) {

                if (unplacedDrag.hasClass('infinite')) {

                    var noOfDrags = thisQ.noOfDropsInGroup(thisQ.getGroup(unplacedDrag));

                    var cloneDrags = thisQ.getInfiniteDragClones(unplacedDrag, false);

                    if (cloneDrags.length < noOfDrags) {

                        var cloneDrag = unplacedDrag.clone();

                        hiddenDrag.after(cloneDrag);

                        questionManager.addEventHandlersToDrag(cloneDrag);

                    } else {

                        hiddenDrag.addClass('active');

                    }

                } else {

                    hiddenDrag.addClass('active');

                }

            }

            // Send the drag to drop.

            thisQ.sendDragToDrop(thisQ.getUnplacedChoice(thisQ.getGroup(input), choice), drop);

        });

        // Save the question answer.

        thisQ.questionAnswer = thisQ.getQuestionAnsweredValues();

    };

    /**

     * Get the question answered values.

     *

     * @return {Object} Contain key-value with key is the input id and value is the input value.

     */

    DragDropToTextQuestion.prototype.getQuestionAnsweredValues = function() {

        let result = {};

        this.getRoot().find('input.placeinput').each((i, inputNode) => {

            result[inputNode.id] = inputNode.value;

        });

        return result;

    };

    /**

     * Check if the question is being interacted or not.

     *

     * @return {boolean} Return true if the user has changed the question-answer.

     */

    DragDropToTextQuestion.prototype.isQuestionInteracted = function() {

        const oldAnswer = this.questionAnswer;

        const newAnswer = this.getQuestionAnsweredValues();

        let isInteracted = false;

        // First, check both answers have the same structure or not.

        if (JSON.stringify(newAnswer) !== JSON.stringify(oldAnswer)) {

            isInteracted = true;

            return isInteracted;

        }

        // Check the values.

        Object.keys(newAnswer).forEach(key => {

            if (newAnswer[key] !== oldAnswer[key]) {

                isInteracted = true;

            }

        });

        return isInteracted;

    };

    /**

     * Handles the start of dragging an item.

     *

     * @param {Event} e the touch start or mouse down event.

     */

    DragDropToTextQuestion.prototype.handleDragStart = function(e) {

        var thisQ = this,

            drag = $(e.target).closest('.draghome');

        var info = dragDrop.prepare(e);

        if (!info.start || drag.hasClass('beingdragged')) {

            return;

        }

        drag.addClass('beingdragged');

        var currentPlace = this.getClassnameNumericSuffix(drag, 'inplace');

        if (currentPlace !== null) {

            this.setInputValue(currentPlace, 0);

            drag.removeClass('inplace' + currentPlace);

            var hiddenDrop = thisQ.getDrop(drag, currentPlace);

            if (hiddenDrop.length) {

                hiddenDrop.addClass('active');

                drag.offset(hiddenDrop.offset());

            }

        } else {

            var hiddenDrag = thisQ.getDragClone(drag);

            if (hiddenDrag.length) {

                if (drag.hasClass('infinite')) {

                    var noOfDrags = this.noOfDropsInGroup(this.getGroup(drag));

                    var cloneDrags = this.getInfiniteDragClones(drag, false);

                    if (cloneDrags.length < noOfDrags) {

                        var cloneDrag = drag.clone();

                        cloneDrag.removeClass('beingdragged');

                        hiddenDrag.after(cloneDrag);

                        questionManager.addEventHandlersToDrag(cloneDrag);

                        drag.offset(cloneDrag.offset());

                    } else {

                        hiddenDrag.addClass('active');

                        drag.offset(hiddenDrag.offset());

                    }

                } else {

                    hiddenDrag.addClass('active');

                    drag.offset(hiddenDrag.offset());

                }

            }

        }

        dragDrop.start(e, drag, function(x, y, drag) {

            thisQ.dragMove(x, y, drag);

        }, function(x, y, drag) {

            thisQ.dragEnd(x, y, drag);

        });

    };

    /**

     * Called whenever the currently dragged items moves.

     *

     * @param {Number} pageX the x position.

     * @param {Number} pageY the y position.

     * @param {jQuery} drag the item being moved.

     */

    DragDropToTextQuestion.prototype.dragMove = function(pageX, pageY, drag) {

        var thisQ = this;

        this.getRoot().find('span.group' + this.getGroup(drag)).not('.beingdragged').each(function(i, dropNode) {

            var drop = $(dropNode);

            if (thisQ.isPointInDrop(pageX, pageY, drop)) {

                drop.addClass('valid-drag-over-drop');

            } else {

                drop.removeClass('valid-drag-over-drop');

            }

        });

    };

    /**

     * Called when user drops a drag item.

     *

     * @param {Number} pageX the x position.

     * @param {Number} pageY the y position.

     * @param {jQuery} drag the item being moved.

     */

    DragDropToTextQuestion.prototype.dragEnd = function(pageX, pageY, drag) {

        var thisQ = this,

            root = this.getRoot(),

            placed = false;

        root.find('span.group' + this.getGroup(drag)).not('.beingdragged').each(function(i, dropNode) {

            if (placed) {

                return false;

            }

            const dropZone = $(dropNode);

            if (!thisQ.isPointInDrop(pageX, pageY, dropZone)) {

                // Not this drop zone.

                return true;

            }

            let drop = null;

            if (dropZone.hasClass('placed')) {

                // This is an placed drag item in a drop.

                dropZone.removeClass('valid-drag-over-drop');

                // Get the correct drop.

                drop = thisQ.getDrop(drag, thisQ.getClassnameNumericSuffix(dropZone, 'inplace'));

            } else {

                // Empty drop.

                drop = dropZone;

            }

            // Now put this drag into the drop.

            drop.removeClass('valid-drag-over-drop');

            thisQ.sendDragToDrop(drag, drop);

            placed = true;

            return false; // Stop the each() here.

        });

        if (!placed) {

            this.sendDragHome(drag);

        }

    };

    /**

     * Animate a drag item into a given place (or back home).

     *

     * @param {jQuery|null} drag the item to place. If null, clear the place.

     * @param {jQuery} drop the place to put it.

     */

    DragDropToTextQuestion.prototype.sendDragToDrop = function(drag, drop) {

        // Send drag home if there is no place in drop.

        if (this.getPlace(drop) === null) {

            this.sendDragHome(drag);

            return;

        }

        // Is there already a drag in this drop? if so, evict it.

        var oldDrag = this.getCurrentDragInPlace(this.getPlace(drop));

        if (oldDrag.length !== 0) {

            var currentPlace = this.getClassnameNumericSuffix(oldDrag, 'inplace');

            // When infinite group and there is already a drag in a drop, reject the exact clone in the same drop.

            if (this.hasDropSameDrag(currentPlace, drop, oldDrag, drag)) {

                this.sendDragHome(drag);

                return;

            }

            var hiddenDrop = this.getDrop(oldDrag, currentPlace);

            hiddenDrop.addClass('active');

            oldDrag.addClass('beingdragged');

            oldDrag.offset(hiddenDrop.offset());

            this.sendDragHome(oldDrag);

        }

        if (drag.length === 0) {

            this.setInputValue(this.getPlace(drop), 0);

            if (drop.data('isfocus')) {

                drop.focus();

            }

        } else {

            // Prevent the drag item drop into two drop-zone.

            if (this.getClassnameNumericSuffix(drag, 'inplace')) {

                return;

            }

            this.setInputValue(this.getPlace(drop), this.getChoice(drag));

            drag.removeClass('unplaced')

                .addClass('placed inplace' + this.getPlace(drop));

            drag.attr('tabindex', 0);

            this.animateTo(drag, drop);

        }

    };

    /**

     * When infinite group and there is already a drag in a drop, reject the exact clone in the same drop.

     *

     * @param {int} currentPlace  the position of the current drop.

     * @param {jQuery} drop the drop containing a drag.

     * @param {jQuery} oldDrag the drag already placed in drop.

     * @param {jQuery} drag the new drag which is exactly the same (clone) as oldDrag .

     * @returns {boolean}

     */

    DragDropToTextQuestion.prototype.hasDropSameDrag = function(currentPlace, drop, oldDrag, drag) {

        if (drag.hasClass('infinite')) {

            return drop.hasClass('place' + currentPlace) &&

                this.getGroup(drag) === this.getGroup(drop) &&

                this.getChoice(drag) === this.getChoice(oldDrag) &&

                this.getGroup(drag) === this.getGroup(oldDrag);

        }

        return false;

    };

    /**

     * Animate a drag back to its home.

     *

     * @param {jQuery} drag the item being moved.

     */

    DragDropToTextQuestion.prototype.sendDragHome = function(drag) {

        var currentPlace = this.getClassnameNumericSuffix(drag, 'inplace');

        if (currentPlace !== null) {

            drag.removeClass('inplace' + currentPlace);

        }

        drag.data('unplaced', true);

        this.animateTo(drag, this.getDragHome(this.getGroup(drag), this.getChoice(drag)));

    };

    /**

     * Handles keyboard events on drops.

     *

     * Drops are focusable. Once focused, right/down/space switches to the next choice, and

     * left/up switches to the previous. Escape clear.

     *

     * @param {KeyboardEvent} e

     */

    DragDropToTextQuestion.prototype.handleKeyPress = function(e) {

        var drop = $(e.target).closest('.drop');

        if (drop.length === 0) {

            var placedDrag = $(e.target);

            var currentPlace = this.getClassnameNumericSuffix(placedDrag, 'inplace');

            if (currentPlace !== null) {

                drop = this.getDrop(placedDrag, currentPlace);

            }

        }

        var currentDrag = this.getCurrentDragInPlace(this.getPlace(drop)),

            nextDrag = $();

        switch (e.keyCode) {

            case keys.space:

            case keys.arrowRight:

            case keys.arrowDown:

                nextDrag = this.getNextDrag(this.getGroup(drop), currentDrag);

                break;

            case keys.arrowLeft:

            case keys.arrowUp:

                nextDrag = this.getPreviousDrag(this.getGroup(drop), currentDrag);

                break;

            case keys.escape:

                break;

            default:

                questionManager.isKeyboardNavigation = false;

                return; // To avoid the preventDefault below.

        }

        if (nextDrag.length) {

            nextDrag.data('isfocus', true);

            nextDrag.addClass('beingdragged');

            var hiddenDrag = this.getDragClone(nextDrag);

            if (hiddenDrag.length) {

                if (nextDrag.hasClass('infinite')) {

                    var noOfDrags = this.noOfDropsInGroup(this.getGroup(nextDrag));

                    var cloneDrags = this.getInfiniteDragClones(nextDrag, false);

                    if (cloneDrags.length < noOfDrags) {

                        var cloneDrag = nextDrag.clone();

                        cloneDrag.removeClass('beingdragged');

                        cloneDrag.removeAttr('tabindex');

                        hiddenDrag.after(cloneDrag);

                        questionManager.addEventHandlersToDrag(cloneDrag);

                        nextDrag.offset(cloneDrag.offset());

                    } else {

                        hiddenDrag.addClass('active');

                        nextDrag.offset(hiddenDrag.offset());

                    }

                } else {

                    hiddenDrag.addClass('active');

                    nextDrag.offset(hiddenDrag.offset());

                }

            }

        } else {

            drop.data('isfocus', true);

        }

        e.preventDefault();

        this.sendDragToDrop(nextDrag, drop);

    };

    /**

     * Choose the next drag in a group.

     *

     * @param {int} group which group.

     * @param {jQuery} drag current choice (empty jQuery if there isn't one).

     * @return {jQuery} the next drag in that group, or null if there wasn't one.

     */

    DragDropToTextQuestion.prototype.getNextDrag = function(group, drag) {

        var choice,

            numChoices = this.noOfChoicesInGroup(group);

        if (drag.length === 0) {

            choice = 1; // Was empty, so we want to select the first choice.

        } else {

            choice = this.getChoice(drag) + 1;

        }

        var next = this.getUnplacedChoice(group, choice);

        while (next.length === 0 && choice < numChoices) {

            choice++;

            next = this.getUnplacedChoice(group, choice);

        }

        return next;

    };

    /**

     * Choose the previous drag in a group.

     *

     * @param {int} group which group.

     * @param {jQuery} drag current choice (empty jQuery if there isn't one).

     * @return {jQuery} the next drag in that group, or null if there wasn't one.

     */

    DragDropToTextQuestion.prototype.getPreviousDrag = function(group, drag) {

        var choice;

        if (drag.length === 0) {

            choice = this.noOfChoicesInGroup(group);

        } else {

            choice = this.getChoice(drag) - 1;

        }

        var previous = this.getUnplacedChoice(group, choice);

        while (previous.length === 0 && choice > 1) {

            choice--;

            previous = this.getUnplacedChoice(group, choice);

        }

        // Does this choice exist?

        return previous;

    };

    /**

     * Animate an object to the given destination.

     *

     * @param {jQuery} drag the element to be animated.

     * @param {jQuery} target element marking the place to move it to.

     */

    DragDropToTextQuestion.prototype.animateTo = function(drag, target) {

        var currentPos = drag.offset(),

            targetPos = target.offset(),

            thisQ = this;

        M.util.js_pending('qtype_ddwtos-animate-' + thisQ.containerId);

        // Animate works in terms of CSS position, whereas locating an object

        // on the page works best with jQuery offset() function. So, to get

        // the right target position, we work out the required change in

        // offset() and then add that to the current CSS position.

        drag.animate(

            {

                left: parseInt(drag.css('left')) + targetPos.left - currentPos.left,

                top: parseInt(drag.css('top')) + targetPos.top - currentPos.top

            },

            {

                duration: 'fast',

                done: function() {

                    $('body').trigger('qtype_ddwtos-dragmoved', [drag, target, thisQ]);

                    M.util.js_complete('qtype_ddwtos-animate-' + thisQ.containerId);

                }

            }

        );

    };

    /**

     * Detect if a point is inside a given DOM node.

     *

     * @param {Number} pageX the x position.

     * @param {Number} pageY the y position.

     * @param {jQuery} drop the node to check (typically a drop).

     * @return {boolean} whether the point is inside the node.

     */

    DragDropToTextQuestion.prototype.isPointInDrop = function(pageX, pageY, drop) {

        var position = drop.offset();

        return pageX >= position.left && pageX < position.left + drop.width()

                && pageY >= position.top && pageY < position.top + drop.height();

    };

    /**

     * Set the value of the hidden input for a place, to record what is currently there.

     *

     * @param {int} place which place to set the input value for.

     * @param {int} choice the value to set.

     */

    DragDropToTextQuestion.prototype.setInputValue = function(place, choice) {

        this.getRoot().find('input.placeinput.place' + place).val(choice);

    };

    /**

     * Get the outer div for this question.

     *

     * @returns {jQuery} containing that div.

     */

    DragDropToTextQuestion.prototype.getRoot = function() {

        return $(document.getElementById(this.containerId));

    };

    /**

     * Get drag home for a given choice.

     *

     * @param {int} group the group.

     * @param {int} choice the choice number.

     * @returns {jQuery} containing that div.

     */

    DragDropToTextQuestion.prototype.getDragHome = function(group, choice) {

        if (!this.getRoot().find('.draghome.dragplaceholder.group' + group + '.choice' + choice).is(':visible')) {

            return this.getRoot().find('.draggrouphomes' + group +

                ' span.draghome.infinite' +

                '.choice' + choice +

                '.group' + group);

        }

        return this.getRoot().find('.draghome.dragplaceholder.group' + group + '.choice' + choice);

    };

    /**

     * Get an unplaced choice for a particular group.

     *

     * @param {int} group the group.

     * @param {int} choice the choice number.

     * @returns {jQuery} jQuery wrapping the unplaced choice. If there isn't one, the jQuery will be empty.

     */

    DragDropToTextQuestion.prototype.getUnplacedChoice = function(group, choice) {

        return this.getRoot().find('.draghome.group' + group + '.choice' + choice + '.unplaced').slice(0, 1);

    };

    /**

     * Get the drag that is currently in a given place.

     *

     * @param {int} place the place number.

     * @return {jQuery} the current drag (or an empty jQuery if none).

     */

    DragDropToTextQuestion.prototype.getCurrentDragInPlace = function(place) {

        return this.getRoot().find('span.draghome.inplace' + place);

    };

    /**

     * Return the number of blanks in a given group.

     *

     * @param {int} group the group number.

     * @returns {int} the number of drops.

     */

    DragDropToTextQuestion.prototype.noOfDropsInGroup = function(group) {

        return this.getRoot().find('.drop.group' + group).length;

    };

    /**

     * Return the number of choices in a given group.

     *

     * @param {int} group the group number.

     * @returns {int} the number of choices.

     */

    DragDropToTextQuestion.prototype.noOfChoicesInGroup = function(group) {

        return this.getRoot().find('.draghome.group' + group).length;

    };

    /**

     * Return the number at the end of the CSS class name with the given prefix.

     *

     * @param {jQuery} node

     * @param {String} prefix name prefix

     * @returns {Number|null} the suffix if found, else null.

     */

    DragDropToTextQuestion.prototype.getClassnameNumericSuffix = function(node, prefix) {

        var classes = node.attr('class');

        if (classes !== undefined && classes !== '') {

            var classesArr = classes.split(' ');

            for (var index = 0; index < classesArr.length; index++) {

                var patt1 = new RegExp('^' + prefix + '([0-9])+$');

                if (patt1.test(classesArr[index])) {

                    var patt2 = new RegExp('([0-9])+$');

                    var match = patt2.exec(classesArr[index]);

                    return Number(match[0]);

                }

            }

        }

        return null;

    };

    /**

     * Get the choice number of a drag.

     *

     * @param {jQuery} drag the drag.

     * @returns {Number} the choice number.

     */

    DragDropToTextQuestion.prototype.getChoice = function(drag) {

        return this.getClassnameNumericSuffix(drag, 'choice');

    };

    /**

     * Given a DOM node that is significant to this question

     * (drag, drop, ...) get the group it belongs to.

     *

     * @param {jQuery} node a DOM node.

     * @returns {Number} the group it belongs to.

     */

    DragDropToTextQuestion.prototype.getGroup = function(node) {

        return this.getClassnameNumericSuffix(node, 'group');

    };

    /**

     * Get the place number of a drop, or its corresponding hidden input.

     *

     * @param {jQuery} node the DOM node.

     * @returns {Number} the place number.

     */

    DragDropToTextQuestion.prototype.getPlace = function(node) {

        return this.getClassnameNumericSuffix(node, 'place');

    };

    /**

     * Get drag clone for a given drag.

     *

     * @param {jQuery} drag the drag.

     * @returns {jQuery} the drag's clone.

     */

    DragDropToTextQuestion.prototype.getDragClone = function(drag) {

        return this.getRoot().find('.draggrouphomes' +

            this.getGroup(drag) +

            ' span.draghome' +

            '.choice' + this.getChoice(drag) +

            '.group' + this.getGroup(drag) +

            '.dragplaceholder');

    };

    /**

     * Get infinite drag clones for given drag.

     *

     * @param {jQuery} drag the drag.

     * @param {Boolean} inHome in the home area or not.

     * @returns {jQuery} the drag's clones.

     */

    DragDropToTextQuestion.prototype.getInfiniteDragClones = function(drag, inHome) {

        if (inHome) {

            return this.getRoot().find('.draggrouphomes' +

                this.getGroup(drag) +

                ' span.draghome' +

                '.choice' + this.getChoice(drag) +

                '.group' + this.getGroup(drag) +

                '.infinite').not('.dragplaceholder');

        }

        return this.getRoot().find('span.draghome' +

            '.choice' + this.getChoice(drag) +

            '.group' + this.getGroup(drag) +

            '.infinite').not('.dragplaceholder');

    };

    /**

     * Get drop for a given drag and place.

     *

     * @param {jQuery} drag the drag.

     * @param {Integer} currentPlace the current place of drag.

     * @returns {jQuery} the drop's clone.

     */

    DragDropToTextQuestion.prototype.getDrop = function(drag, currentPlace) {

        return this.getRoot().find('.drop.group' + this.getGroup(drag) + '.place' + currentPlace);

    };

    /**

     * Singleton that tracks all the DragDropToTextQuestions on this page, and deals

     * with event dispatching.

     *

     * @type {Object}

     */

    var questionManager = {

        /**

         * {boolean} used to ensure the event handlers are only initialised once per page.

         */

        eventHandlersInitialised: false,

        /**

         * {Object} ensures that the drag event handlers are only initialised once per question,

         * indexed by containerId (id on the .que div).

         */

        dragEventHandlersInitialised: {},

        /**

         * {boolean} is keyboard navigation or not.

         */

        isKeyboardNavigation: false,

        /**

         * {DragDropToTextQuestion[]} all the questions on this page, indexed by containerId (id on the .que div).

         */

        questions: {},

        /**

         * Initialise questions.

         *

         * @param {String} containerId id of the outer div for this question.

         * @param {boolean} readOnly whether the question is being displayed read-only.

         */

        init: function(containerId, readOnly) {

            questionManager.questions[containerId] = new DragDropToTextQuestion(containerId, readOnly);

            if (!questionManager.eventHandlersInitialised) {

                questionManager.setupEventHandlers();

                questionManager.eventHandlersInitialised = true;

            }

            if (!questionManager.dragEventHandlersInitialised.hasOwnProperty(containerId)) {

                questionManager.dragEventHandlersInitialised[containerId] = true;

                // We do not use the body event here to prevent the other event on Mobile device, such as scroll event.

                var questionContainer = document.getElementById(containerId);

                if (questionContainer.classList.contains('ddwtos') &&

                    !questionContainer.classList.contains('qtype_ddwtos-readonly')) {

                    // TODO: Convert all the jQuery selectors and events to native Javascript.

                    questionManager.addEventHandlersToDrag($(questionContainer).find('span.draghome'));

                }

            }

        },

        /**

         * Set up the event handlers that make this question type work. (Done once per page.)

         */

        setupEventHandlers: function() {

            $('body')

                .on('keydown',

                    '.que.ddwtos:not(.qtype_ddwtos-readonly) span.drop',

                    questionManager.handleKeyPress)

                .on('keydown',

                    '.que.ddwtos:not(.qtype_ddwtos-readonly) span.draghome.placed:not(.beingdragged)',

                    questionManager.handleKeyPress)

                .on('qtype_ddwtos-dragmoved', questionManager.handleDragMoved);

        },

        /**

         * Binding the drag/touch event again for newly created element.

         *

         * @param {jQuery} element Element to bind the event

         */

        addEventHandlersToDrag: function(element) {

            // Unbind all the mousedown and touchstart events to prevent double binding.

            element.unbind('mousedown touchstart');

            element.on('mousedown touchstart', questionManager.handleDragStart);

        },

        /**

         * Handle mouse down / touch start on drags.

         * @param {Event} e the DOM event.

         */

        handleDragStart: function(e) {

            e.preventDefault();

            var question = questionManager.getQuestionForEvent(e);

            if (question) {

                question.handleDragStart(e);

            }

        },

        /**

         * Handle key down / press on drops.

         * @param {KeyboardEvent} e

         */

        handleKeyPress: function(e) {

            if (questionManager.isKeyboardNavigation) {

                return;

            }

            questionManager.isKeyboardNavigation = true;

            var question = questionManager.getQuestionForEvent(e);

            if (question) {

                question.handleKeyPress(e);

            }

        },

        /**

         * Given an event, work out which question it affects.

         *

         * @param {Event} e the event.

         * @returns {DragDropToTextQuestion|undefined} The question, or undefined.

         */

        getQuestionForEvent: function(e) {

            var containerId = $(e.currentTarget).closest('.que.ddwtos').attr('id');

            return questionManager.questions[containerId];

        },

        /**

         * Handle when drag moved.

         *

         * @param {Event} e the event.

         * @param {jQuery} drag the drag

         * @param {jQuery} target the target

         * @param {DragDropToTextQuestion} thisQ the question.

         */

        handleDragMoved: function(e, drag, target, thisQ) {

            drag.removeClass('beingdragged');

            drag.css('top', '').css('left', '');

            target.after(drag);