feat: parse YouTube video links and page types

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

.gitignore

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+node_modules/
+.DS_Store

package.json

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+{
+  "name": "outlier-saver-extension",
+  "version": "0.1.0",
+  "private": true,
+  "type": "module",
+  "scripts": {
+    "test": "node --test"
+  }
+}

src/lib/video-id.js

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+const ID_RE = /^[A-Za-z0-9_-]{11}$/;
+const YOUTUBE_HOSTS = new Set(['www.youtube.com', 'youtube.com', 'm.youtube.com']);
+
+export function isVideoId(value) {
+  return typeof value === 'string' && ID_RE.test(value);
+}
+
+// Returns { videoId, isShort } for a link to a single video, or null for anything else.
+export function parseVideoLink(href, base = 'https://www.youtube.com') {
+  if (!href) return null;
+  let url;
+  try {
+    url = new URL(href, base);
+  } catch {
+    return null;
+  }
+  if (!YOUTUBE_HOSTS.has(url.hostname)) return null;
+
+  if (url.pathname === '/watch') {
+    const id = url.searchParams.get('v');
+    return isVideoId(id) ? { videoId: id, isShort: false } : null;
+  }
+  const shorts = url.pathname.match(/^\/shorts\/([^/]+)/);
+  if (shorts && isVideoId(shorts[1])) return { videoId: shorts[1], isShort: true };
+  return null;
+}
+
+export function pageFromPath(pathname) {
+  if (pathname === '/') return 'home';
+  if (pathname === '/watch') return 'watch';
+  if (pathname === '/results') return 'search';
+  if (/^\/(@[^/]+|channel\/[^/]+|c\/[^/]+|user\/[^/]+)/.test(pathname)) return 'channel';
+  return null;
+}

test/video-id.test.js

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+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { isVideoId, pageFromPath, parseVideoLink } from '../src/lib/video-id.js';
+
+test('isVideoId accepts only 11-character IDs', () => {
+  assert.equal(isVideoId('dQw4w9WgXcQ'), true);
+  assert.equal(isVideoId('abc_DEF-123'), true);
+  for (const value of ['short', 'waytoolongvideoid', 'has space!!', '', null, undefined, 12345678901]) {
+    assert.equal(isVideoId(value), false, String(value));
+  }
+});
+
+test('parseVideoLink reads an absolute watch URL', () => {
+  assert.deepEqual(parseVideoLink('https://www.youtube.com/watch?v=dQw4w9WgXcQ'), {
+    videoId: 'dQw4w9WgXcQ',
+    isShort: false,
+  });
+});
+
+test('parseVideoLink reads a relative watch href with extra params', () => {
+  assert.deepEqual(parseVideoLink('/watch?v=dQw4w9WgXcQ&t=42s&list=PL123'), {
+    videoId: 'dQw4w9WgXcQ',
+    isShort: false,
+  });
+});
+
+test('parseVideoLink marks /shorts/ links as shorts', () => {
+  assert.deepEqual(parseVideoLink('/shorts/abcdefghijk'), { videoId: 'abcdefghijk', isShort: true });
+  assert.deepEqual(parseVideoLink('/shorts/abcdefghijk?feature=share'), {
+    videoId: 'abcdefghijk',
+    isShort: true,
+  });
+});
+
+test('parseVideoLink ignores links that are not a single video', () => {
+  for (const href of ['/', '/@mrbeast', '/playlist?list=PL123', '/feed/subscriptions', '/results?search_query=x']) {
+    assert.equal(parseVideoLink(href), null, href);
+  }
+});
+
+test('parseVideoLink rejects malformed IDs', () => {
+  for (const href of [
+    '/watch',
+    '/watch?v=',
+    '/watch?v=short',
+    '/watch?v=waytoolongvideoid',
+    '/shorts/toolongidtoolong',
+  ]) {
+    assert.equal(parseVideoLink(href), null, href);
+  }
+});
+
+test('parseVideoLink rejects other hosts and garbage', () => {
+  assert.equal(parseVideoLink('https://evil.example.com/watch?v=dQw4w9WgXcQ'), null);
+  for (const href of [null, undefined, '', 'http://[bad']) {
+    assert.equal(parseVideoLink(href), null, String(href));
+  }
+});
+
+test('pageFromPath maps the four supported page types', () => {
+  assert.equal(pageFromPath('/'), 'home');
+  assert.equal(pageFromPath('/watch'), 'watch');
+  assert.equal(pageFromPath('/results'), 'search');
+  for (const path of ['/@mrbeast', '/@mrbeast/videos', '/channel/UC123/videos', '/c/name', '/user/name']) {
+    assert.equal(pageFromPath(path), 'channel', path);
+  }
+});
+
+test('pageFromPath returns null for unsupported pages', () => {
+  for (const path of ['/feed/subscriptions', '/shorts/abcdefghijk', '/playlist', '/premium']) {
+    assert.equal(pageFromPath(path), null, path);
+  }
+});