# Pattern

## What is it

A tabs component that provides different sections of content that are displayed one at a time when the user selects that information.

## When to use it

The tabbed user interface enables users to jump to their target section quickly. Tabs present like logically group information on the same page. Information should

- be logically chunked and ordered
- be arallel in nature
- show user's context
- obvious where they begin and end

Users should not need to see content of multiple tabs simultaneously and the user should be able to easily recognise where they are within the content.

## How to use it

The structure of the tab set is defined in html. There are two forms supported. Adding a class of `.tab-group` to the container element will work in place of the `tabset` tag, and the tab panels can be defined using either `tab=""` or `data-tab=""`. Passing an optional element to the init function will initialise tabs within that element.

    tabset#uniqueID
    	div(tab="[tab title]")
    	div(tab="[tab title]")

    tabset, .tab-group {
    	margin: 2rem 0 1rem 0;
    }
    tabset > ul, .tab-group > ul {
    	display: -webkit-box;
    	display: -ms-flexbox;
    	display: flex;
    	margin: 0;
    	padding: 0;
    }
    tabset > ul li.separator, .tab-group > ul li.separator {
    	border-bottom: 1px solid #7f7f7f;
    	border-left: 1px solid #7f7f7f;
    	display: inline-block;
    	margin: 0.45rem 0 0 0;
    	width: 100%;
    }
    tabset .tab-hidden, .tab-group .tab-hidden {
    	display: none;
    }
    tabset [role=tab], .tab-group [role=tab] {
    	background-color: #FFF;
    	border-left: 1px solid #7f7f7f;
    	border-top: 1px solid #7f7f7f;
    	border-radius: 0.5rem 0.5rem 0 0;
    	cursor: pointer;
    	margin: 0;
    	display: inline;
    	padding: 1rem 1.5rem 0.14rem 1.5rem;
    	z-index: 2;
    }
    tabset [role=tab]:last-of-type, .tab-group [role=tab]:last-of-type {
    	border-right: 1px solid #7f7f7f;
    }
    tabset [role=tab]:not(.selected), .tab-group [role=tab]:not(.selected) {
    	background-color: #f0f0f0;
    	border-bottom: 1px solid #7f7f7f;
    }
    tabset [role=tab] span, .tab-group [role=tab] span {
    	display: block;
    	margin: 0 0 0.5rem 0;
    }
    tabset [role=tabpanel], .tab-group [role=tabpanel] {
    	background-color: #FFF;
    	border: 1px solid #7f7f7f;
    	border-top: none;
    	padding: 1rem;
    	z-index: 1;
    }
    tabset [role=tabpanel]:not(.open), .tab-group [role=tabpanel]:not(.open) {
    	display: none;
    }

    @import "scss/core/tabs/_tabs";
    @include tabs{
    	// optional content block
    };

    //		DS2 core (c) 2024 Alexander McIlwraith
    //		Licensed under CC BY-SA 4.0

    $tab-border: #7f7f7f !default;
    $tab-selected: #FFF !default;
    $tab-notselected: #f0f0f0 !default;

    @mixin tabs {
    	tabset, .tab-group {
    		margin: 2rem 0 1rem 0;
    		> ul {
    			display: flex;
    			margin: 0;
    			padding: 0;

    			li.separator {
    				border-bottom: 1px solid $tab-border;
    				border-left: 1px solid $tab-border;
    				display: inline-block;
    				margin: .45rem 0 0 0;
    				width: 100%;
    			}
    		}

    		.tab-hidden {
    			display: none;
    		}

    		[role="tab"] {
    			background-color: $tab-selected;
    			border-left: 1px solid $tab-border;
    			border-top: 1px solid $tab-border;
    			border-radius: .5rem .5rem 0 0;
    			cursor:pointer;
    			margin: 0;
    			display: inline;
    			padding: 1rem 1.5rem .14rem 1.5rem;
    			z-index: 2;

    			&:last-of-type {
    				border-right: 1px solid $tab-border;
    			}

    			&:not(.selected) {
    				background-color: $tab-notselected;
    				border-bottom: 1px solid $tab-border;
    			}

    			span {
    				display: block;
    				margin: 0 0 .5rem 0;
    			}

    		}
    		[role="tabpanel"] {
    			background-color: $tab-selected;
    			border: 1px solid $tab-border;
    			border-top: none;
    			padding: 1rem;
    			z-index: 1;

    			&:not(.open) {
    				display: none;
    			}
    			@content;

    		}
    	}
    }

    import * as tabs from "./js/core/tabs/_tabs.js";
    tabs.init();

    /*  DS2 core (c) 2024 Alexander McIlwraith
    	import * as tabs from "../pg/patterns/layouts/tabs/_tabs.js";
    	tabs.init();
     */

    export function init(p = document) {
    	p.querySelectorAll(".tab-group, tabset").forEach(tabGroup => {

    		if (tabGroup.querySelector("[role=tablist]") === null) {
    			const tabgroup = tabGroup.getAttribute("id");
    			let tablist = "";

    			Array.from(tabGroup.children).forEach(child => {
    				const tab = child.getAttribute("tab") || child.getAttribute("data-tab");
    				if (tab !== null) {
    					const tabID = tab.replace(/\W+/g, "-").toLowerCase();
    					const tabPanel = document.createElement('div');
    					tabPanel.id = `tab-panel-${tabgroup}-${tabID}`;
    					tabPanel.className = tablist === "" ? "open" : "";
    					tabPanel.setAttribute("role", "tabpanel");
    					tabPanel.setAttribute("tabindex", "0");
    					tabPanel.setAttribute("aria-labelledby", `tab-${tabgroup}-${tabID}`);
    					tabPanel.appendChild(child.cloneNode(true));
    					child.parentNode.replaceChild(tabPanel, child);
    					tablist += `${tab}`;
    				} else {
    					child.classList.add("tab-hidden");
    				}
    			});

    			const ul = document.createElement('ul');
    			ul.setAttribute("role", "tablist");
    			ul.innerHTML = `${tablist}`;
    			tabGroup.insertBefore(ul, tabGroup.firstChild);

    			tabGroup.querySelectorAll('[role="tab"]').forEach(tab => {
    				tab.addEventListener("click", () => {
    					const siblings = Array.from(tab.parentNode.children);
    					siblings.forEach(sibling => sibling.classList.remove("selected"));
    					tab.classList.add("selected");

    					const tabPanels = Array.from(tab.parentNode.parentNode.children)
    										   .filter(child => child.getAttribute("role") === "tabpanel");
    					tabPanels.forEach(panel => panel.classList.remove("open"));

    					const tabPanelId = tab.getAttribute("id").replace("tab", "tab-panel");
    					document.getElementById(tabPanelId).classList.add("open");
    				});
    			});

    		}
    	});
    }