1 files changed, 85 insertions, 0 deletions
diff --git a/src/js/feed.js b/src/js/feed.js
new file mode 100644
index 0000000..50ebfcd
--- /dev/null
+++ b/src/js/feed.js
@@ -0,0 +1,85 @@
+/// <reference lib="es2022" />
+
+import { $, $$, on, dispatch, halts, attr, next, prev, asHtml, hotkey, behavior, makelogger } from "./19.js"
+
+const ilog = makelogger("feed");
+const sFeed = "[role=feed]";
+const sScopedArticle = ":scope > article, :scope > [role=article]";
+const sArticle = "article, [role=article]";
+const sFocusable = ":is(a, area)[href], :is(button, details, embed, iframe, label, select, textarea):not([disabled]), :is(audio, video)[controls], :is(img, object)[usemap], [tabindex]:not([tabindex='-1'])"
+
+/**
+ * @param {HTMLElement} feed
+ * @returns {HTMLElement[]}
+ */
+const articles = feed => $$(feed, sScopedArticle);
+
+
+/**
+ * @param {HTMLElement} feed
+ * @param {HTMLElement} activeElement
+ * @returns {null}
+ */
+const focusPreviousArticle = (feed, activeElement) => asHtml(prev(feed, sArticle, activeElement, {wrap: false}))?.focus();
+
+
+/**
+ * @param {HTMLElement} feed
+ * @param {HTMLElement} activeElement
+ * @returns {null}
+ */
+const focusNextArticle = (feed, activeElement) => asHtml(next(feed, sArticle, activeElement.closest(sArticle), {wrap: false}))?.focus();
+
+
+/**
+ * @param {HTMLElement} article
+ * @returns {null}
+ */
+const focusOutsideFeed = article => asHtml(article.parentElement.closest(sArticle))?.focus();
+
+
+/**
+ * @param {HTMLElement} activeElement
+ * @returns {null}
+ */
+const focusInsideFeed = activeElement => asHtml($(activeElement.closest(sArticle), sArticle))?.focus();
+
+
+/**
+ * @param {HTMLElement} feed
+ * @returns {null}
+ */
+const focusBeforeFeed = feed => asHtml(prev(document.body, sFocusable, feed, {}))?.focus();
+
+
+/**
+ * @param {HTMLElement} feed
+ * @returns {null}
+ */
+const focusAfterFeed = feed => asHtml(next(document.body, sFocusable, feed, {}))?.focus();
+
+
+export const feed = behavior(sFeed, (feed, { root }) => {
+
+    if (!(feed instanceof HTMLElement)) return;
+
+    feed.setAttribute("aria-busy", "false");
+    articles(feed).forEach((article, idx, articles) => {
+        article.setAttribute("tabindex", "0");
+        article.setAttribute("aria-posinset", idx + 1);
+        article.setAttribute("aria-setsize", articles.length);
+        if (!(article.hasAttribute("aria-labelledby") || article.hasAttribute("aria-label")))
+            console.error("Article", article, "has no accessible name (aria-label or aria-labelledby)");
+    });
+
+    on(feed, "keydown", hotkey({
+        "PageUp": halts("default propagation", _ => focusPreviousArticle(feed, root.activeElement)),
+        "PageDown": halts("default propagation", _ => focusNextArticle(feed, root.activeElement)),
+        "Alt+PageUp": halts("default", _ => focusOutsideFeed(root.activeElement)),
+        "Alt+PageDown": halts("default", _ => focusInsideFeed(root.activeElement)),
+        "Ctrl+Home": halts("default propagation", _ => focusBeforeFeed(feed)),
+        "Ctrl+End": halts("default propagation", _ => focusAfterFeed(feed)),
+    }));
+});
+
+feed(document);