From 3d894bf54170b0ad0b643058118b615876250ea2 Mon Sep 17 00:00:00 2001
From: stereobooster <stereobooster@gmail.com>
Date: Thu, 30 May 2019 14:30:40 +0200
Subject: [PATCH] Fully accessible component

---
 src/components/Accordion.js        | 89 ++++++++++++++++++++++++++----
 src/components/AccordionSection.js | 18 +++++-
 2 files changed, 96 insertions(+), 11 deletions(-)

diff --git a/src/components/Accordion.js b/src/components/Accordion.js
index 80b994d..a99a26b 100644
--- a/src/components/Accordion.js
+++ b/src/components/Accordion.js
@@ -1,6 +1,18 @@
-import React from "react";
+import React, {
+  useRef,
+  createContext,
+  useContext,
+  useState,
+  useMemo
+} from "react";
 import styles from "./Accordion.module.css";
 
+const AccordionContext = createContext({
+  focusRef: {},
+  selected: null
+});
+export const useAccordionContext = () => useContext(AccordionContext);
+
 /**
  * Accordion according to Accordion Design Pattern in WAI-ARIA Authoring Practices 1.1
  * see https://www.w3.org/TR/wai-aria-practices/examples/accordion/accordion.html
@@ -17,17 +29,74 @@ Shift + Tab
   👍 Moves focus to the previous focusable element.
   👍 All focusable elements in the accordion are included in the page Tab sequence.
 Down Arrow
-  👎 When focus is on an accordion header, moves focus to the next accordion header.
-  👎 When focus is on last accordion header, moves focus to first accordion header.
+  👍 When focus is on an accordion header, moves focus to the next accordion header.
+  👍 When focus is on last accordion header, moves focus to first accordion header.
 Up Arrow
-  👎 When focus is on an accordion header, moves focus to the previous accordion header.
-  👎 When focus is on first accordion header, moves focus to last accordion header.
+  👍 When focus is on an accordion header, moves focus to the previous accordion header.
+  👍 When focus is on first accordion header, moves focus to last accordion header.
 Home
-  👎 When focus is on an accordion header, moves focus to the first accordion header.
+  👍 When focus is on an accordion header, moves focus to the first accordion header.
 End
-  👎 When focus is on an accordion header, moves focus to the last accordion header.
+  👍 When focus is on an accordion header, moves focus to the last accordion header.
 ```
  */
-export const Accordion = ({ children }) => (
-  <div className={styles.Accordion}>{children}</div>
-);
+export const Accordion = ({ children }) => {
+  const focusRef = useRef(null);
+  const [selected, setSelected] = useState(null);
+  const context = useMemo(
+    () => ({
+      focusRef,
+      selected
+    }),
+    [selected]
+  );
+
+  return (
+    <div
+      className={styles.Accordion}
+      onKeyDown={e => {
+        switch (e.key) {
+          case "ArrowDown":
+            {
+              const ids = React.Children.map(children, child => child.props.id);
+              const index = ids.findIndex(x => x === focusRef.current);
+              if (index >= ids.length - 1) {
+                setSelected(ids[0]);
+              } else {
+                setSelected(ids[index + 1]);
+              }
+            }
+            break;
+          case "ArrowUp":
+            {
+              const ids = React.Children.map(children, child => child.props.id);
+              const index = ids.findIndex(x => x === focusRef.current);
+              if (index <= 0) {
+                setSelected(ids[ids.length - 1]);
+              } else {
+                setSelected(ids[index - 1]);
+              }
+            }
+            break;
+          case "Home":
+            {
+              const ids = React.Children.map(children, child => child.props.id);
+              setSelected(ids[0]);
+            }
+            break;
+          case "End":
+            {
+              const ids = React.Children.map(children, child => child.props.id);
+              setSelected(ids[ids.length - 1]);
+            }
+            break;
+          default:
+        }
+      }}
+    >
+      <AccordionContext.Provider value={context}>
+        {children}
+      </AccordionContext.Provider>
+    </div>
+  );
+};
diff --git a/src/components/AccordionSection.js b/src/components/AccordionSection.js
index 1f47005..7c66ac6 100644
--- a/src/components/AccordionSection.js
+++ b/src/components/AccordionSection.js
@@ -1,5 +1,6 @@
-import React from "react";
+import React, { useRef, useEffect } from "react";
 import styles from "./AccordionSection.module.css";
+import { useAccordionContext } from "./Accordion";
 
 export const AccordionSection = ({
   children,
@@ -11,6 +12,14 @@ export const AccordionSection = ({
   const sectionId = `section-${id}`;
   const labelId = `label-${id}`;
 
+  const { focusRef, selected } = useAccordionContext();
+  const labelRef = useRef();
+  useEffect(() => {
+    if (id === selected && labelRef.current) {
+      labelRef.current.focus();
+    }
+  }, [id, selected]);
+
   return (
     <>
       <div
@@ -30,6 +39,13 @@ export const AccordionSection = ({
             default:
           }
         }}
+        onFocus={() => {
+          focusRef.current = id;
+        }}
+        onBlur={() => {
+          focusRef.current = null;
+        }}
+        ref={labelRef}
       >
         {title}
         <span aria-hidden={true}>{expanded ? "▲" : "▼"}</span>