1 files changed, 158 insertions, 0 deletions
diff --git a/devtools/client/accessibility/reducers/accessibles.js b/devtools/client/accessibility/reducers/accessibles.js
new file mode 100644
index 0000000000..908d1b734d
--- /dev/null
+++ b/devtools/client/accessibility/reducers/accessibles.js
@@ -0,0 +1,158 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+"use strict";
+
+const {
+  AUDIT,
+  FETCH_CHILDREN,
+  HIGHLIGHT,
+  RESET,
+  SELECT,
+} = require("resource://devtools/client/accessibility/constants.js");
+
+/**
+ * Initial state definition
+ */
+function getInitialState() {
+  return new Map();
+}
+
+/**
+ * Maintain a cache of received accessibles responses from the backend.
+ */
+function accessibles(state = getInitialState(), action) {
+  switch (action.type) {
+    case FETCH_CHILDREN:
+      return onReceiveChildren(state, action);
+    case HIGHLIGHT:
+    case SELECT:
+      return onReceiveAncestry(state, action);
+    case AUDIT:
+      return onAudit(state, action);
+    case RESET:
+      return getInitialState();
+    default:
+      return state;
+  }
+}
+
+function getActorID(accessible) {
+  return accessible.actorID || accessible._form?.actor;
+}
+
+/**
+ * If accessible is cached recursively remove all its children and remove itself
+ * from cache.
+ * @param {Map}    cache      Previous state maintaining a cache of previously
+ *                            fetched accessibles.
+ * @param {Object} accessible Accessible object to remove from cache.
+ */
+function cleanupChild(cache, accessible) {
+  const actorID = getActorID(accessible);
+  const cached = cache.get(actorID);
+  if (!cached) {
+    return;
+  }
+
+  for (const child of cached.children) {
+    cleanupChild(cache, child);
+  }
+
+  cache.delete(actorID);
+}
+
+/**
+ * Determine if accessible in cache is stale. Accessible object is stale if its
+ * cached children array has the size other than the value of its childCount
+ * property that updates on accessible actor event.
+ * @param {Map}    cache      Previous state maintaining a cache of previously
+ *                             fetched accessibles.
+ * @param {Object} accessible Accessible object to test for staleness.
+ */
+function staleChildren(cache, accessible) {
+  const cached = cache.get(getActorID(accessible));
+  if (!cached) {
+    return false;
+  }
+
+  return cached.children.length !== accessible.childCount;
+}
+
+function updateChildrenCache(cache, accessible, children) {
+  const actorID = getActorID(accessible);
+
+  if (cache.has(actorID)) {
+    const cached = cache.get(actorID);
+    for (const child of cached.children) {
+      // If exhisting children cache includes an accessible that is not present
+      // any more or if child accessible is stale remove it and all its children
+      // from cache.
+      if (!children.includes(child) || staleChildren(cache, child)) {
+        cleanupChild(cache, child);
+      }
+    }
+    cached.children = children;
+    cache.set(actorID, cached);
+  } else {
+    cache.set(actorID, { children });
+  }
+
+  return cache;
+}
+
+function updateAncestry(cache, ancestry) {
+  ancestry.forEach(({ accessible, children }) =>
+    updateChildrenCache(cache, accessible, children)
+  );
+
+  return cache;
+}
+
+/**
+ * Handles fetching of accessible children.
+ * @param {Map}     cache  Previous state maintaining a cache of previously
+ *                         fetched accessibles.
+ * @param {Object}  action Redux action object.
+ * @return {Object} updated state
+ */
+function onReceiveChildren(cache, action) {
+  const { error, accessible, response: children } = action;
+  if (!error) {
+    return updateChildrenCache(new Map(cache), accessible, children);
+  }
+
+  if (!accessible.isDestroyed()) {
+    console.warn(`Error fetching children: `, error);
+    return cache;
+  }
+
+  const newCache = new Map(cache);
+  cleanupChild(newCache, accessible);
+  return newCache;
+}
+
+function onReceiveAncestry(cache, action) {
+  const { error, response: ancestry } = action;
+  if (error) {
+    console.warn(`Error fetching ancestry: `, error);
+    return cache;
+  }
+
+  return updateAncestry(new Map(cache), ancestry);
+}
+
+function onAudit(cache, action) {
+  const { error, response: ancestries } = action;
+  if (error) {
+    console.warn(`Error performing an audit: `, error);
+    return cache;
+  }
+
+  const newCache = new Map(cache);
+  ancestries.forEach(ancestry => updateAncestry(newCache, ancestry));
+
+  return newCache;
+}
+
+exports.accessibles = accessibles;