3dom4wf7p: Publish public text posts from a feed composer

src/lib/post-client.ts

@@ -0,0 +1,80 @@
+// Browser-side text-post publishing. The composer text is only cleared after
+// the new post id shows up on the reloaded first page of the home feed.
+
+import { fetchFeedPage, FeedLoadError, type FeedPage } from "./feed-client";
+
+export class PostError extends Error {
+  constructor(public readonly signedOut: boolean) {
+    super(signedOut ? "sign_in" : "publish_failed");
+  }
+}
+
+export async function sendPost(content: string, fetchImpl: typeof fetch = fetch): Promise<string> {
+  let res: Response;
+  try {
+    res = await fetchImpl("/api/posts", {
+      method: "POST",
+      credentials: "same-origin",
+      headers: { "Content-Type": "application/json" },
+      body: JSON.stringify({ content }),
+    });
+  } catch {
+    throw new PostError(false);
+  }
+  if (res.status === 401) throw new PostError(true);
+  if (!res.ok) throw new PostError(false);
+  try {
+    const b = (await res.json()) as { id?: unknown };
+    if ((typeof b.id === "string" && b.id) || typeof b.id === "number") return String(b.id);
+  } catch {
+    /* fall through */
+  }
+  throw new PostError(false);
+}
+
+function pageHasPost(page: FeedPage, id: string): boolean {
+  return page.items.some((item) => {
+    const post = (item as { post?: { id?: unknown } } | null)?.post;
+    return post != null && String(post.id) === id;
+  });
+}
+
+/**
+ * Reload the first page. Returns the page when it holds the post id, else null.
+ * Throws PostError when the person is signed out or the reload fails.
+ */
+export async function confirmOnFirstPage(
+  id: string,
+  fetchPage: (cursor: string | null) => Promise<FeedPage> = fetchFeedPage,
+): Promise<FeedPage | null> {
+  try {
+    const page = await fetchPage(null);
+    return pageHasPost(page, id) ? page : null;
+  } catch (e) {
+    throw new PostError(e instanceof FeedLoadError && e.signedOut);
+  }
+}
+
+export interface PublishDeps {
+  send?: (content: string) => Promise<string>;
+  fetchPage?: (cursor: string | null) => Promise<FeedPage>;
+}
+
+/**
+ * Publish text and confirm it on the reloaded first page. Returns that page
+ * only when the post id is on it. `unconfirmed` holds an id that was created
+ * earlier but not yet seen, so a retry re-checks the feed and does not create
+ * a duplicate. Throws PostError otherwise; the caller keeps the composer text.
+ */
+export async function publishAndConfirm(
+  content: string,
+  unconfirmed: { id: string | null },
+  deps: PublishDeps = {},
+): Promise<FeedPage> {
+  const id = unconfirmed.id ?? (await (deps.send ?? sendPost)(content));
+  unconfirmed.id = id;
+  const page = await confirmOnFirstPage(id, deps.fetchPage);
+  if (!page) throw new PostError(false);
+  unconfirmed.id = null;
+  return page;
+}