feat: add content script that collects video ids from YouTube pages

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/content.js

@@ -0,0 +1,76 @@
+(async () => {
+  const { parseVideoLink, pageFromPath } = await import(chrome.runtime.getURL('src/lib/video-id.js'));
+  const { readVidiqScore } = await import(chrome.runtime.getURL('src/lib/vidiq.js'));
+
+  const LINK_SELECTOR = 'a[href*="/watch?v="], a[href*="/shorts/"]';
+  // Only used to find the element that contains a VidIQ badge; ID collection does not depend on it.
+  const CARD_SELECTOR = [
+    'ytd-rich-item-renderer',
+    'ytd-video-renderer',
+    'ytd-compact-video-renderer',
+    'ytd-grid-video-renderer',
+    'yt-lockup-view-model',
+    'ytm-shorts-lockup-view-model',
+    'ytd-reel-item-renderer',
+  ].join(',');
+  const SCAN_INTERVAL_MS = 500;
+
+  // videoId -> true if already sent together with a VidIQ score, false if sent without one.
+  let sent = new Map();
+  let scanTimer = null;
+
+  function collectItems(page) {
+    const items = new Map();
+    const consider = (parsed, card) => {
+      const state = sent.get(parsed.videoId);
+      if (state === true) return;
+      const vidiqScore = readVidiqScore(card);
+      if (state === false && vidiqScore === null) return;
+      const item = items.get(parsed.videoId) ?? {
+        videoId: parsed.videoId,
+        vidiqScore: null,
+        viaShortsUrl: false,
+        page,
+      };
+      item.vidiqScore ??= vidiqScore;
+      item.viaShortsUrl ||= parsed.isShort;
+      items.set(parsed.videoId, item);
+    };
+
+    for (const link of document.querySelectorAll(LINK_SELECTOR)) {
+      const parsed = parseVideoLink(link.getAttribute('href'));
+      if (parsed) consider(parsed, link.closest(CARD_SELECTOR) ?? link.parentElement);
+    }
+    if (page === 'watch') {
+      const current = parseVideoLink(location.href);
+      if (current) consider(current, null);
+    }
+    return [...items.values()];
+  }
+
+  function scan() {
+    scanTimer = null;
+    const page = pageFromPath(location.pathname);
+    if (!page) return;
+    const items = collectItems(page);
+    if (items.length === 0) return;
+    for (const item of items) sent.set(item.videoId, item.vidiqScore !== null);
+    try {
+      chrome.runtime.sendMessage({ type: 'videos-seen', items }).catch(() => {});
+    } catch {
+      observer.disconnect(); // the extension was reloaded; this script is orphaned
+    }
+  }
+
+  function scheduleScan() {
+    if (scanTimer === null) scanTimer = setTimeout(scan, SCAN_INTERVAL_MS);
+  }
+
+  const observer = new MutationObserver(scheduleScan);
+  observer.observe(document.documentElement, { childList: true, subtree: true });
+  document.addEventListener('yt-navigate-finish', () => {
+    sent = new Map();
+    scheduleScan();
+  });
+  scheduleScan();
+})();