Tabs

window.a11yTabs = (function tabsComponentIIFE(global, document) {
	const tabInstances = new WeakMap();
	const className = 'o-tab-list';
	const tablistElement = document.querySelector(`.js-${className}`);
	let updateURLFromHash;

	if (tablistElement) {
		updateURLFromHash = tablistElement.getAttribute('data-update-url');
	}

	/**
	* Instantiates the component
	* @constructor
	* @param {DOM Node} element
	*/
	const TabComponent = function TabComponent(element, options) {
		if (!element || !element.nodeType) {
			return;
		}

		const namespace = getComputedStyle(tablistElement, ':before').content.replace(/["']/g, '');

		const defaults = {
			tabList: `.${namespace}${className}`,
			tabItem: `.${namespace}${className}__item`,
			tabLink: `.${namespace}${className}__link`,
			tabPanel: `.${namespace}o-tab-panel`,
		};

		this.options = Object.assign(defaults, options);

		this.element = element;
		this.tabList = element.querySelector(this.options.tabList);
		this.tabItems = [].slice.call(
			this.tabList.querySelectorAll(this.options.tabItem),
		);
		this.tabLinks = [].slice.call(
			this.tabList.querySelectorAll(this.options.tabLink),
		);
		this.tabPanels = [].slice.call(
			element.querySelectorAll(this.options.tabPanel),
		);

		this.currentIndex = 0;

		this.tabList.setAttribute('role', 'tablist');

		this.tabItems.forEach((item, index) => {
			item.setAttribute('role', 'presentation');

			if (index === 0) {
				item.setAttribute('data-tab-active', '');
			}
		});

		this.tabLinks.forEach((item, index) => {
			item.setAttribute('role', 'tab');

			if (index > 0) {
				item.setAttribute('tabindex', '-1');
			} else {
				item.setAttribute('aria-selected', 'true');
			}
		});

		this.tabPanels.forEach((item, index) => {
			item.setAttribute('role', 'tabpanel');
			item.setAttribute('aria-labelledby', `tab${index}`);
			item.setAttribute('tabindex', '-1');

			if (index > 0) {
				item.setAttribute('hidden', '');
			}
		});

		this.eventCallback = handleEvents.bind(this); // eslint-disable-line
		this.tabList.addEventListener('click', this.eventCallback, false);
		this.tabList.addEventListener('keydown', this.eventCallback, false);

		tabInstances.set(this.element, this);

		// Select the correct tab based on URL hash
		if (updateURLFromHash) {
			this.selectTabFromHash();
		}
	};

	TabComponent.prototype = {
		/**
		* Event handler for all tab interactions
		* @param {number} index - Index of the tab being activiated
		* @param {string} direction -
		*/
		handleTabInteraction: function handleTabInteraction(index, direction) {
			const { currentIndex } = this;
			let newIndex = index;

			// The click event does not pass in a direction. This is for keyboard support
			if (direction) {
				if (direction === 37) {
					newIndex = index - 1;
				} else {
					newIndex = index + 1;
				}
			}

			// Supports continuous tabbing when reaching beginning or end of tab list
			if (newIndex < 0) {
				newIndex = this.tabLinks.length - 1;
			} else if (newIndex === this.tabLinks.length) {
				newIndex = 0;
			}

			// update tabs
			this.tabLinks[currentIndex].setAttribute('tabindex', '-1');
			this.tabLinks[currentIndex].removeAttribute('aria-selected');
			this.tabItems[currentIndex].removeAttribute('data-tab-active');

			this.tabLinks[newIndex].setAttribute('aria-selected', 'true');
			this.tabItems[newIndex].setAttribute('data-tab-active', '');
			this.tabLinks[newIndex].removeAttribute('tabindex');
			this.tabLinks[newIndex].focus(); // Focus the newly selected tab

			// update tab panels
			this.tabPanels[currentIndex].setAttribute('hidden', '');
			this.tabPanels[newIndex].removeAttribute('hidden');

			// Update the browser's URL hash to reflect the current tab's ID
			const selectedTabId = this.tabLinks[newIndex].id;

			if (updateURLFromHash) {
				window.history.pushState(null, '', `#${selectedTabId}`);
			}

			this.currentIndex = newIndex;

			return this;
		},

		/**
		* Set tab panel focus
		* @param {number} index - Tab panel index to receive focus
		*/
		handleTabpanelFocus: function handleTabPanelFocus(index) {
			this.tabPanels[index].focus();

			return this;
		},
		/**
		 * Selects a tab based on the URL hash
		 */
		selectTabFromHash() {
			const { hash } = global.location;
			if (hash) {
				const targetId = hash.substring(1); // Remove the '#' character
				const targetIndex = this.tabLinks.findIndex((link) => link.id === targetId);
				if (targetIndex !== -1) {
					this.handleTabInteraction(targetIndex);
				}
			}
		},
	};

	/**
	* Creates or returns existing component
	* @param {string} selector
	*/
	function createTabComponent(selector, options) {
		const elements = document.querySelectorAll(selector);
		[].forEach.call(elements, (element) => tabInstances.get(element)
		|| new TabComponent(element, options));
	}

	/**
	* Destroys an existing component
	* @param {DOM Node} element
	*/
	function destroyTabComponent(element) {
		if (!element || !element.nodeType) {
			return;
		}

		const component = tabInstances.get(element);
		component.tabList.removeAttribute('role', 'tablist');

		component.tabItems.forEach((item, index) => {
			item.removeAttribute('role', 'presentation');

			if (index === 0) {
				item.removeAttribute('data-tab-active');
			}
		});

		component.tabLinks.forEach((item, index) => {
			item.removeAttribute('role', 'tab');
			item.removeAttribute('id', `tab${index}`);

			if (index > 0) {
				item.removeAttribute('tabindex', '-1');
			} else {
				item.removeAttribute('aria-selected', 'true');
			}
		});

		component.tabPanels.forEach((item, index) => {
			item.removeAttribute('role', 'tabpanel');
			item.removeAttribute('aria-labelledby', `tab${index}`);
			item.removeAttribute('tabindex', '-1');

			if (index > 0) {
				item.removeAttribute('hidden');
			}
		});

		component.tabList.removeEventListener('click', component.eventCallback);
		component.tabList.removeEventListener('keydown', component.eventCallback);
		tabInstances.delete(component.element);
	}

	/**
	* Handles all event listener callbacks
	* @param {event} event
	*/
	function handleEvents(event) {
		if (event.type === 'click') {
			event.preventDefault();
			TabComponent.prototype.handleTabInteraction.call(
				this,
				this.tabLinks.indexOf(event.target),
			);
		}

		if (event.type === 'keydown') {
			const index = this.tabLinks.indexOf(event.target);

			// Left and right arrows
			if (event.which === 37 || event.which === 39) {
				event.preventDefault();
				TabComponent.prototype.handleTabInteraction.call(
					this,
					index,
					event.which,
				);
			}

			// Down arrow
			if (event.which === 40) {
				event.preventDefault();
				TabComponent.prototype.handleTabpanelFocus.call(this, index);
			}
		}
	}

	return {
		create: createTabComponent,
		destroy: destroyTabComponent,
	};
}(window, document));

const tabComponent = a11yTabs.create('[data-tab-component]'); // eslint-disable-line