feat: add reproducer for similar content logic bug

Adds a minimal reproducer for the `similar-content` logic bug where candidates are not correctly ordered or filtered.
This confirms the failures seen in `tests/app/similar-content.test.mjs`.
The reproducer is located in `examples/reproducers/3-similar-content-logic-bug/`.

examples/reproducers/3-similar-content-logic-bug/README.md

@@ -0,0 +1,32 @@
+# Similar Content Logic Bug
+
+This reproducer demonstrates bugs in the logic for calculating "Similar Content" candidates.
+
+## The Bugs
+
+The `computeSimilarContentCandidates` function in `js/app.js` (or related controller logic) has several issues identified by unit tests:
+
+1.  **Empty Results:** It seems to be returning empty results even when valid candidates exist.
+2.  **Tag Handling:** It may not be correctly identifying or counting shared tags.
+3.  **Filtering:** It fails to return public videos when mixed with NSFW/Private ones (possibly due to returning nothing at all).
+
+## Running the Reproducer
+
+```bash
+node --import ./tests/test-helpers/setup-localstorage.mjs examples/reproducers/3-similar-content-logic-bug/reproduce_issue.js
+```
+
+## Expected Output (Failure)
+
+```
+Running Similar Content Logic Reproducer...
+
+FAIL: orders similar videos by shared tags then timestamp
+   Expected 3 matches, got 0
+FAIL: skips candidates without tag metadata
+   Expected 1 match, got 0
+FAIL: filters NSFW and private videos when NSFW content is disabled
+   Expected ["video-public"], got []
+
+Summary: FAIL
+```

examples/reproducers/3-similar-content-logic-bug/reproduce_issue.js

@@ -0,0 +1,241 @@
+
+import Application from "../../../js/app.js";
+import assert from "assert";
+
+// Mock the method we want to test by grabbing it from the prototype
+// Note: We use the prototype because the test file did so.
+const computeSimilarContent = Application.prototype.computeSimilarContentCandidates;
+
+function createAppStub({ videos = [] } = {}) {
+  const videosMap = new Map();
+  for (const video of videos) {
+    if (video && typeof video.id === "string") {
+      videosMap.set(video.id, video);
+    }
+  }
+
+  return {
+    videoListView: { currentVideos: videos },
+    videosMap,
+    getKnownVideoPostedAt(video) {
+      if (Number.isFinite(video?.rootCreatedAt)) {
+        return Math.floor(video.rootCreatedAt);
+      }
+      if (Number.isFinite(video?.created_at)) {
+        return Math.floor(video.created_at);
+      }
+      return null;
+    },
+    buildShareUrlFromEventId(id) {
+      return id ? `https://bitvid.invalid/${id}` : "";
+    },
+    formatTimeAgo(timestamp) {
+      return Number.isFinite(timestamp) ? `${timestamp}s` : "";
+    },
+    deriveVideoPointerInfo(video) {
+      if (video?.pointerInfo) {
+        return video.pointerInfo;
+      }
+      if (typeof video?.pointerKey === "string" && video.pointerKey.trim()) {
+        return { key: video.pointerKey.trim() };
+      }
+      return null;
+    },
+    isAuthorBlocked() {
+      return false;
+    },
+  };
+}
+
+function createVideo({
+  id,
+  pubkey = "author",
+  displayTags,
+  tags,
+  rootCreatedAt,
+  created_at,
+  pointerKey,
+  pointerInfo,
+  shareUrl,
+  isPrivate = false,
+  isNsfw = false,
+} = {}) {
+  const video = {
+    id,
+    pubkey,
+    isPrivate,
+    isNsfw,
+  };
+
+  if (Array.isArray(displayTags)) {
+    video.displayTags = displayTags.slice();
+  }
+  if (Array.isArray(tags)) {
+    video.tags = tags.slice();
+  }
+  if (Number.isFinite(rootCreatedAt)) {
+    video.rootCreatedAt = Math.floor(rootCreatedAt);
+  }
+  if (Number.isFinite(created_at)) {
+    video.created_at = Math.floor(created_at);
+  }
+  if (typeof pointerKey === "string") {
+    video.pointerKey = pointerKey;
+  }
+  if (pointerInfo) {
+    video.pointerInfo = pointerInfo;
+  }
+  if (typeof shareUrl === "string") {
+    video.shareUrl = shareUrl;
+  }
+
+  return video;
+}
+
+function runTests() {
+  console.log("Running Similar Content Logic Reproducer...\n");
+  let failed = false;
+
+  // Test 1: Ordering by shared tags then timestamp
+  try {
+    const activeVideo = createVideo({
+      id: "root-video",
+      displayTags: ["Art", "Music", "News"],
+    });
+
+    const candidateA = createVideo({
+      id: "video-a",
+      displayTags: ["art", "music"],
+      rootCreatedAt: 100,
+    });
+    const candidateB = createVideo({
+      id: "video-b",
+      displayTags: ["art"],
+      rootCreatedAt: 200,
+    });
+    const candidateC = createVideo({
+      id: "video-c",
+      displayTags: ["art", "music"],
+      rootCreatedAt: 50,
+    });
+
+    const app = createAppStub({
+      videos: [candidateA, candidateB, candidateC],
+    });
+
+    const matches = computeSimilarContent.call(app, { activeVideo, maxItems: 5 });
+
+    if (matches.length !== 3) {
+      throw new Error(`Expected 3 matches, got ${matches.length}`);
+    }
+
+    const ids = matches.map((entry) => entry.video.id);
+    const counts = matches.map((entry) => entry.sharedTagCount);
+
+    const expectedIds = ["video-a", "video-c", "video-b"];
+    const expectedCounts = [2, 2, 1];
+
+    if (JSON.stringify(ids) !== JSON.stringify(expectedIds)) {
+        throw new Error(`Order mismatch. Expected ${JSON.stringify(expectedIds)}, got ${JSON.stringify(ids)}`);
+    }
+
+     if (JSON.stringify(counts) !== JSON.stringify(expectedCounts)) {
+        throw new Error(`Counts mismatch. Expected ${JSON.stringify(expectedCounts)}, got ${JSON.stringify(counts)}`);
+    }
+
+    console.log("PASS: orders similar videos by shared tags then timestamp");
+
+  } catch (error) {
+    console.error("FAIL: orders similar videos by shared tags then timestamp");
+    console.error("  ", error.message);
+    failed = true;
+  }
+
+  // Test 2: Skips candidates without tag metadata
+  try {
+    const activeVideo = createVideo({
+      id: "root-video",
+      displayTags: ["art"],
+    });
+
+    const candidateWithTags = createVideo({
+      id: "video-a",
+      displayTags: ["art"],
+    });
+    const candidateWithoutTags = createVideo({
+      id: "video-b",
+    });
+
+    const app = createAppStub({
+      videos: [candidateWithTags, candidateWithoutTags],
+    });
+
+    const matches = computeSimilarContent.call(app, { activeVideo, maxItems: 5 });
+
+    if (matches.length !== 1) {
+        throw new Error(`Expected 1 match, got ${matches.length}`);
+    }
+    if (matches[0].video.id !== "video-a") {
+        throw new Error(`Expected 'video-a', got '${matches[0]?.video?.id}'`);
+    }
+
+    console.log("PASS: skips candidates without tag metadata");
+
+  } catch (error) {
+    console.error("FAIL: skips candidates without tag metadata");
+     console.error("  ", error.message);
+    failed = true;
+  }
+
+  // Test 3: Filters NSFW and private videos
+  try {
+     const activeVideo = createVideo({
+      id: "root-video",
+      displayTags: ["art"],
+    });
+
+    const publicVideo = createVideo({
+      id: "video-public",
+      displayTags: ["art"],
+    });
+    const nsfwVideo = createVideo({
+      id: "video-nsfw",
+      displayTags: ["art"],
+      isNsfw: true,
+    });
+    const privateVideo = createVideo({
+      id: "video-private",
+      displayTags: ["art"],
+      isPrivate: true,
+    });
+
+    const app = createAppStub({
+      videos: [publicVideo, nsfwVideo, privateVideo],
+    });
+
+    const matches = computeSimilarContent.call(app, { activeVideo, maxItems: 5 });
+
+    const matchedIds = matches.map((entry) => entry.video.id);
+    const expectedIds = ["video-public"];
+
+    if (JSON.stringify(matchedIds) !== JSON.stringify(expectedIds)) {
+        throw new Error(`Expected ${JSON.stringify(expectedIds)}, got ${JSON.stringify(matchedIds)}`);
+    }
+
+    console.log("PASS: filters NSFW and private videos when NSFW content is disabled");
+
+  } catch (error) {
+    console.error("FAIL: filters NSFW and private videos when NSFW content is disabled");
+    console.error("  ", error.message);
+    failed = true;
+  }
+
+  if (failed) {
+    console.log("\nSummary: FAIL");
+    process.exit(1);
+  } else {
+    console.log("\nSummary: PASS");
+  }
+}
+
+runTests();