Add feed discovery plugin

plugins/feed-discovery/src/dedupe.ts

@@ -0,0 +1,38 @@
+import type { DiscoveredFeed } from "./types.js";
+import { canonicalizeUrl } from "./url-safety.js";
+
+export function dedupeFeeds(feeds: DiscoveredFeed[]) {
+  const byKey = new Map<string, DiscoveredFeed>();
+
+  for (const feed of feeds) {
+    const key = dedupeKey(feed);
+    const existing = byKey.get(key);
+    if (!existing || feed.score > existing.score || feed.confidence > existing.confidence) {
+      byKey.set(key, mergeFeed(existing, feed));
+    }
+  }
+
+  return [...byKey.values()].sort((a, b) => b.score - a.score || b.confidence - a.confidence);
+}
+
+function dedupeKey(feed: DiscoveredFeed) {
+  const feedUrl = feed.canonicalFeedUrl || feed.feedUrl;
+  try {
+    return `feed:${canonicalizeUrl(feedUrl)}`;
+  } catch {
+    return `feed:${feedUrl.toLowerCase()}`;
+  }
+}
+
+function mergeFeed(existing: DiscoveredFeed | undefined, next: DiscoveredFeed): DiscoveredFeed {
+  if (!existing) {
+    return next;
+  }
+
+  return {
+    ...existing,
+    ...next,
+    tags: [...new Set([...existing.tags, ...next.tags])],
+    sampleItems: next.sampleItems?.length ? next.sampleItems : existing.sampleItems
+  };
+}