feat: add client-side episode title hydration

static/player/episodes/titles.ts

@@ -0,0 +1,69 @@
+import { state } from "../state";
+
+type EpisodeTitle = { number: number; title: string };
+
+const episodeElements = (): HTMLElement[] => {
+  const elements: HTMLElement[] = [];
+  for (const container of [state.elements.episodeGrid, state.elements.episodeList]) {
+    container?.querySelectorAll<HTMLElement>("[data-episode-id]").forEach((element) => {
+      elements.push(element);
+    });
+  }
+  return elements;
+};
+
+const hasMissingTitles = (): boolean =>
+  episodeElements().some((element) => {
+    const number = Number.parseInt(element.dataset.episodeId ?? "", 10);
+    return number > 0 && element.dataset.episodeTitle?.trim() === `Episode ${number}`;
+  });
+
+export const parseEpisodeTitles = (value: unknown): EpisodeTitle[] => {
+  if (!Array.isArray(value)) {
+    return [];
+  }
+  return value.flatMap((item): EpisodeTitle[] => {
+    if (typeof item !== "object" || item === null) {
+      return [];
+    }
+    const candidate = item as { number?: unknown; title?: unknown };
+    if (
+      typeof candidate.number !== "number" ||
+      !Number.isInteger(candidate.number) ||
+      candidate.number <= 0 ||
+      typeof candidate.title !== "string" ||
+      candidate.title.trim() === ""
+    ) {
+      return [];
+    }
+    return [{ number: candidate.number, title: candidate.title.trim() }];
+  });
+};
+
+export const applyEpisodeTitles = (titles: EpisodeTitle[]): void => {
+  const byNumber = new Map(titles.map((episode) => [episode.number, episode.title]));
+  episodeElements().forEach((element) => {
+    const number = Number.parseInt(element.dataset.episodeId ?? "", 10);
+    const title = byNumber.get(number);
+    if (!title) {
+      return;
+    }
+    element.dataset.episodeTitle = title;
+    const label = element.querySelector<HTMLElement>("[data-episode-title]");
+    if (label) {
+      label.textContent = title;
+    }
+  });
+};
+
+export const hydrateEpisodeTitles = async (signal: AbortSignal): Promise<void> => {
+  if (!hasMissingTitles() || state.episode.malID <= 0) {
+    return;
+  }
+
+  const response = await fetch(`/api/watch/episodes/${state.episode.malID}/titles`, { signal });
+  if (!response.ok) {
+    return;
+  }
+  applyEpisodeTitles(parseEpisodeTitles(await response.json()));
+};