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/>.

/**

 * Enhancements to Bootstrap components for accessibility.

 *

 * @module     theme_universe/aria

 * @copyright  2018 Damyon Wiese <damyon@moodle.com>

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

 */

import $ from 'jquery';

import Pending from 'core/pending';

/**

 * Drop downs from bootstrap don't support keyboard accessibility by default.

 */

const dropdownFix = () => {

    let focusEnd = false;

    const setFocusEnd = (end = true) => {

        focusEnd = end;

    };

    const getFocusEnd = () => {

        const result = focusEnd;

        focusEnd = false;

        return result;

    };

    // Special handling for navigation keys when menu is open.

    const shiftFocus = (element, focusCheck = null) => {

        const pendingPromise = new Pending('core/aria:delayed-focus');

        setTimeout(() => {

            if (!focusCheck || focusCheck()) {

                element.focus();

            }

            pendingPromise.resolve();

        }, 50);

    };

    // Event handling for the dropdown menu button.

    const handleMenuButton = e => {

        const trigger = e.key;

        let fixFocus = false;

        // Space key or Enter key opens the menu.

        if (trigger === ' ' || trigger === 'Enter') {

            fixFocus = true;

            // Cancel random scroll.

            e.preventDefault();

            // Open the menu instead.

            e.target.click();

        }

        // Up and Down keys also open the menu.

        if (trigger === 'ArrowUp' || trigger === 'ArrowDown') {

            fixFocus = true;

        }

        if (!fixFocus) {

            // No need to fix the focus. Return early.

            return;

        }

        // Fix the focus on the menu items when the menu is opened.

        const menu = e.target.parentElement.querySelector('[role="menu"]');

        let menuItems = false;

        let foundMenuItem = false;

        let textInput = false;

        if (menu) {

            menuItems = menu.querySelectorAll('[role="menuitem"]');

            textInput = e.target.parentElement.querySelector('[data-action="search"]');

        }

        if (menuItems && menuItems.length > 0) {

            // Up key opens the menu at the end.

            if (trigger === 'ArrowUp') {

                setFocusEnd();

            } else {

                setFocusEnd(false);

            }

            if (getFocusEnd()) {

                foundMenuItem = menuItems[menuItems.length - 1];

            } else {

                // The first menu entry, pretty reasonable.

                foundMenuItem = menuItems[0];

            }

        }

        if (textInput) {

            shiftFocus(textInput);

        }

        if (foundMenuItem && textInput === null) {

            shiftFocus(foundMenuItem);

        }

    };

    // Search for menu items by finding the first item that has

    // text starting with the typed character (case insensitive).

    document.addEventListener('keypress', e => {

        if (e.target.matches('.dropdown [role="menu"] [role="menuitem"]')) {

            const menu = e.target.closest('[role="menu"]');

            if (!menu) {

                return;

            }

            const menuItems = menu.querySelectorAll('[role="menuitem"]');

            if (!menuItems) {

                return;

            }

            const trigger = e.key.toLowerCase();

            for (let i = 0; i < menuItems.length; i++) {

                const item = menuItems[i];

                const itemText = item.text.trim().toLowerCase();

                if (itemText.indexOf(trigger) == 0) {

                    shiftFocus(item);

                    break;

                }

            }

        }

    });

    // Keyboard navigation for arrow keys, home and end keys.

    document.addEventListener('keydown', e => {

        // We only want to set focus when users access the dropdown via keyboard as per

        // guidelines defined in w3 aria practices 1.1 menu-button.

        if (e.target.matches('[data-toggle="dropdown"]')) {

            handleMenuButton(e);

        }

        if (e.target.matches('.dropdown [role="menu"] [role="menuitem"]')) {

            const trigger = e.key;

            let next = false;

            const menu = e.target.closest('[role="menu"]');

            if (!menu) {

                return;

            }

            const menuItems = menu.querySelectorAll('[role="menuitem"]');

            if (!menuItems) {

                return;

            }

            // Down key.

            if (trigger == 'ArrowDown') {

                for (let i = 0; i < menuItems.length - 1; i++) {

                    if (menuItems[i] == e.target) {

                        next = menuItems[i + 1];

                        break;

                    }

                }

                if (!next) {

                    // Wrap to first item.

                    next = menuItems[0];

                }

            } else if (trigger == 'ArrowUp') {

                // Up key.

                for (let i = 1; i < menuItems.length; i++) {

                    if (menuItems[i] == e.target) {

                        next = menuItems[i - 1];

                        break;

                    }

                }

                if (!next) {

                    // Wrap to last item.

                    next = menuItems[menuItems.length - 1];

                }

            } else if (trigger == 'Home') {

                // Home key.

                next = menuItems[0];

            } else if (trigger == 'End') {

                // End key.

                next = menuItems[menuItems.length - 1];

            }

            // Variable next is set if we do want to act on the keypress.

            if (next) {

                e.preventDefault();

                shiftFocus(next);

            }

            return;

        }

    });

    $('.dropdown').on('hidden.bs.dropdown', e => {

        // We need to focus on the menu trigger.

        const trigger = e.target.querySelector('[data-toggle="dropdown"]');

        const focused = document.activeElement != document.body ? document.activeElement : null;

        if (trigger && focused && e.target.contains(focused)) {

            shiftFocus(trigger, () => {

                if (document.activeElement === document.body) {

                    // If the focus is currently on the body, then we can safely assume that the focus needs to be updated.

                    return true;

                }

                // If the focus is on a child of the clicked element still, then update the focus.

                return e.target.contains(document.activeElement);

            });

        }

    });

};

/**

 * A lot of Bootstrap's out of the box features don't work if dropdown items are not focusable.

 */

const comboboxFix = () => {

    $(document).on('show.bs.dropdown', e => {

        if (e.relatedTarget.matches('[role="combobox"]')) {

            const combobox = e.relatedTarget;

            const listbox = document.querySelector(`#${combobox.getAttribute('aria-controls')}[role="listbox"]`);

            if (listbox) {

                const selectedOption = listbox.querySelector('[role="option"][aria-selected="true"]');

                // To make sure ArrowDown doesn't move the active option afterwards.

                setTimeout(() => {

                    if (selectedOption) {

                        selectedOption.classList.add('active');

                        combobox.setAttribute('aria-activedescendant', selectedOption.id);

                    } else {

                        const firstOption = listbox.querySelector('[role="option"]');

                        firstOption.setAttribute('aria-selected', 'true');

                        firstOption.classList.add('active');

                        combobox.setAttribute('aria-activedescendant', firstOption.id);

                    }

                }, 0);

            }

        }

    });

    $(document).on('hidden.bs.dropdown', e => {

        if (e.relatedTarget.matches('[role="combobox"]')) {

            const combobox = e.relatedTarget;

            const listbox = document.querySelector(`#${combobox.getAttribute('aria-controls')}[role="listbox"]`);

            combobox.removeAttribute('aria-activedescendant');

            if (listbox) {

                setTimeout(() => {

                    // Undo all previously highlighted options.

                    listbox.querySelectorAll('.active[role="option"]').forEach(option => {

                        option.classList.remove('active');

                    });

                }, 0);

            }

        }

    });

    // Handling keyboard events for both navigating through and selecting options.

    document.addEventListener('keydown', e => {

        if (e.target.matches('[role="combobox"][aria-controls]:not([aria-haspopup=dialog])')) {

            const combobox = e.target;

            const trigger = e.key;

            let next = null;

            const listbox = document.querySelector(`#${combobox.getAttribute('aria-controls')}[role="listbox"]`);

            const options = listbox.querySelectorAll('[role="option"]');

            const activeOption = listbox.querySelector('.active[role="option"]');

            const editable = combobox.hasAttribute('aria-autocomplete');

            // Under the special case that the dropdown menu is being shown as a result of the key press (like when the user

            // presses ArrowDown or Enter or ... to open the dropdown menu), activeOption is not set yet.

            // It's because of a race condition with show.bs.dropdown event handler.

            if (options && (activeOption || editable)) {

                if (trigger == 'ArrowDown') {

                    for (let i = 0; i < options.length - 1; i++) {

                        if (options[i] == activeOption) {

                            next = options[i + 1];

                            break;

                        }

                    }

                    if (editable && !next) {

                        next = options[0];

                    }

                } if (trigger == 'ArrowUp') {

                    for (let i = 1; i < options.length; i++) {

                        if (options[i] == activeOption) {

                            next = options[i - 1];

                            break;

                        }

                    }

                    if (editable && !next) {

                        next = options[options.length - 1];

                    }

                } else if (trigger == 'Home') {

                    next = options[0];

                } else if (trigger == 'End') {

                    next = options[options.length - 1];

                } else if ((trigger == ' ' && !editable) || trigger == 'Enter') {

                    e.preventDefault();

                    selectOption(combobox, activeOption);

                } else if (!editable) {

                    // Search for options by finding the first option that has

                    // text starting with the typed character (case insensitive).

                    for (let i = 0; i < options.length; i++) {

                        const option = options[i];

                        const optionText = option.textContent.trim().toLowerCase();

                        const keyPressed = e.key.toLowerCase();

                        if (optionText.indexOf(keyPressed) == 0) {

                            next = option;

                            break;

                        }

                    }

                }

                // Variable next is set if we do want to act on the keypress.

                if (next) {

                    e.preventDefault();

                    if (activeOption) {

                        activeOption.classList.remove('active');

                    }

                    next.classList.add('active');

                    combobox.setAttribute('aria-activedescendant', next.id);

                    next.scrollIntoView({block: 'nearest'});

                }

            }

        }

    });

    document.addEventListener('click', e => {

        const option = e.target.closest('[role="listbox"] [role="option"]');

        if (option) {

            const listbox = option.closest('[role="listbox"]');

            const combobox = document.querySelector(`[role="combobox"][aria-controls="${listbox.id}"]`);

            if (combobox) {

                combobox.focus();

                selectOption(combobox, option);

            }

        }

    });

    // In case some code somewhere else changes the value of the combobox.

    document.addEventListener('change', e => {

        if (e.target.matches('input[type="hidden"][id]')) {

            const combobox = document.querySelector(`[role="combobox"][data-input-element="${e.target.id}"]`);

            const option = e.target.parentElement.querySelector(`[role="option"][data-value="${e.target.value}"]`);

            if (combobox && option) {

                selectOption(combobox, option);

            }

        }

    });

    const selectOption = (combobox, option) => {

        const listbox = option.closest('[role="listbox"]');

        const oldSelectedOption = listbox.querySelector('[role="option"][aria-selected="true"]');

        if (oldSelectedOption != option) {

            if (oldSelectedOption) {

                oldSelectedOption.removeAttribute('aria-selected');

            }

            option.setAttribute('aria-selected', 'true');

        }

        if (combobox.hasAttribute('value')) {

            combobox.value = option.textContent.replace(/[\n\r]+|[\s]{2,}/g, ' ').trim();

        } else {

            combobox.textContent = option.textContent;

        }

        if (combobox.dataset.inputElement) {

            const inputElement = document.getElementById(combobox.dataset.inputElement);

            if (inputElement && (inputElement.value != option.dataset.value)) {

                inputElement.value = option.dataset.value;

                inputElement.dispatchEvent(new Event('change', {bubbles: true}));

            }

        }

    };

};

/**

 * After page load, focus on any element with special autofocus attribute.

 */

const autoFocus = () => {

    window.addEventListener("load", () => {

        const alerts = document.querySelectorAll('[data-aria-autofocus="true"][role="alert"]');

        Array.prototype.forEach.call(alerts, autofocusElement => {

            // According to the specification an role="alert" region is only read out on change to the content

            // of that region.

            autofocusElement.innerHTML += ' ';

            autofocusElement.removeAttribute('data-aria-autofocus');

        });

    });

};

/**

 * Changes the focus to the correct tab based on the key that is pressed.

 * @param {KeyboardEvent} e

 */

const updateTabFocus = e => {

    const tabList = e.target.closest('[role="tablist"]');

    const vertical = tabList.getAttribute('aria-orientation') == 'vertical';

    const rtl = window.right_to_left();

    const arrowNext = vertical ? 'ArrowDown' : (rtl ? 'ArrowLeft' : 'ArrowRight');

    const arrowPrevious = vertical ? 'ArrowUp' : (rtl ? 'ArrowRight' : 'ArrowLeft');

    const tabs = Array.prototype.filter.call(

        tabList.querySelectorAll('[role="tab"]'),

        tab => !!tab.offsetHeight); // We only work with the visible tabs.

    for (let i = 0; i < tabs.length; i++) {

        tabs[i].index = i;

    }

    switch (e.key) {

        case arrowNext:

            e.preventDefault();

            if (e.target.index !== undefined && tabs[e.target.index + 1]) {

                tabs[e.target.index + 1].focus();

            } else {

                tabs[0].focus();

            }

            break;

        case arrowPrevious:

            e.preventDefault();

            if (e.target.index !== undefined && tabs[e.target.index - 1]) {

                tabs[e.target.index - 1].focus();

            } else {

                tabs[tabs.length - 1].focus();

            }

            break;

        case 'Home':

            e.preventDefault();

            tabs[0].focus();

            break;

        case 'End':

            e.preventDefault();

            tabs[tabs.length - 1].focus();

    }

};

/**

 * Fix accessibility issues regarding tab elements focus and their tab order in Bootstrap navs.

 */

const tabElementFix = () => {

    document.addEventListener('keydown', e => {

        if (['ArrowUp', 'ArrowDown', 'ArrowLeft', 'ArrowRight', 'Home', 'End'].includes(e.key)) {

            if (e.target.matches('[role="tablist"] [role="tab"]')) {

                updateTabFocus(e);

            }

        }

    });

    document.addEventListener('click', e => {

        if (e.target.matches('[role="tablist"] [data-toggle="tab"], [role="tablist"] [data-toggle="pill"]')) {

            const tabs = e.target.closest('[role="tablist"]').querySelectorAll('[data-toggle="tab"], [data-toggle="pill"]');

            e.preventDefault();

            $(e.target).tab('show');

            tabs.forEach(tab => {

                tab.tabIndex = -1;

            });

            e.target.tabIndex = 0;

        }

    });

};

/**

 * Fix keyboard interaction with Bootstrap Collapse elements.

 *

 * @see {@link https://www.w3.org/TR/wai-aria-practices-1.1/#disclosure|WAI-ARIA Authoring Practices 1.1 - Disclosure (Show/Hide)}

 */

const collapseFix = () => {

    document.addEventListener('keydown', e => {

        if (e.target.matches('[data-toggle="collapse"]')) {

            // Pressing space should toggle expand/collapse.

            if (e.key === ' ') {

                e.preventDefault();

                e.target.click();

            }

        }

    });

};

export const init = () => {

    dropdownFix();

    comboboxFix();

    autoFocus();

    tabElementFix();

    collapseFix();

};