feat(domain): add native-feed detector (Atom/RSS/JSON)

src/domain/native-feed.test.ts

@@ -0,0 +1,65 @@
+import { describe, it, expect } from "vitest";
+import { detectNativeFeeds, unionNativeFeeds } from "./native-feed";
+
+describe("detectNativeFeeds", () => {
+  it("maps the three canonical MIME types to kinds", () => {
+    expect(
+      detectNativeFeeds([
+        { href: "https://x.com/atom", type: "application/atom+xml" },
+        { href: "https://x.com/rss", type: "application/rss+xml" },
+        { href: "https://x.com/json", type: "application/feed+json" },
+      ]),
+    ).toEqual([
+      { url: "https://x.com/atom", type: "atom" },
+      { url: "https://x.com/rss", type: "rss" },
+      { url: "https://x.com/json", type: "json" },
+    ]);
+  });
+
+  it("ignores unknown MIME types (application/json, text/html)", () => {
+    expect(
+      detectNativeFeeds([
+        { href: "https://x.com/api", type: "application/json" },
+        { href: "https://x.com/", type: "text/html" },
+      ]),
+    ).toEqual([]);
+  });
+
+  it("strips MIME parameters and is case-insensitive", () => {
+    expect(
+      detectNativeFeeds([
+        { href: "https://x.com/f", type: "Application/RSS+XML; charset=utf-8" },
+      ]),
+    ).toEqual([{ url: "https://x.com/f", type: "rss" }]);
+  });
+
+  it("dedupes by URL (first kind wins)", () => {
+    expect(
+      detectNativeFeeds([
+        { href: "https://x.com/f", type: "application/rss+xml" },
+        { href: "https://x.com/f", type: "application/atom+xml" },
+      ]),
+    ).toEqual([{ url: "https://x.com/f", type: "rss" }]);
+  });
+});
+
+describe("unionNativeFeeds", () => {
+  it("returns [] for undefined", () => {
+    expect(unionNativeFeeds(undefined)).toEqual([]);
+  });
+
+  it("unions across senders, deduping by URL", () => {
+    expect(
+      unionNativeFeeds({
+        "a@x.com": [{ url: "https://x.com/rss", type: "rss" }],
+        "b@y.com": [
+          { url: "https://x.com/rss", type: "rss" },
+          { url: "https://y.com/atom", type: "atom" },
+        ],
+      }),
+    ).toEqual([
+      { url: "https://x.com/rss", type: "rss" },
+      { url: "https://y.com/atom", type: "atom" },
+    ]);
+  });
+});

src/domain/native-feed.ts

@@ -0,0 +1,54 @@
+/**
+ * Pure detection of a newsletter's own syndication feed. No DOM, no I/O — it
+ * receives already-extracted <link> tuples (infra parses the HTML) and decides
+ * which ones are real feeds. This module owns the business knowledge: the strict
+ * set of recognized feed MIME types.
+ */
+import { NativeFeed } from "../types";
+
+// MIME type → feed kind. Strict: only the three canonical syndication types.
+// `application/json` is deliberately excluded — too broad, captures non-feeds.
+const MIME_TO_KIND: Record<string, NativeFeed["type"]> = {
+  "application/atom+xml": "atom",
+  "application/rss+xml": "rss",
+  "application/feed+json": "json",
+};
+
+// Drop MIME parameters ("; charset=…"), trim, lowercase.
+function normalizeMime(type: string): string {
+  return type.split(";")[0].trim().toLowerCase();
+}
+
+/** Map raw <link> tuples to recognized native feeds, deduped by URL. */
+export function detectNativeFeeds(
+  links: { href: string; type: string }[],
+): NativeFeed[] {
+  const out: NativeFeed[] = [];
+  const seen = new Set<string>();
+  for (const link of links) {
+    const kind = MIME_TO_KIND[normalizeMime(link.type)];
+    if (!kind) continue;
+    const url = link.href.trim();
+    if (!url || seen.has(url)) continue;
+    seen.add(url);
+    out.push({ url, type: kind });
+  }
+  return out;
+}
+
+/** Flatten per-sender native feeds into one list, deduped by URL (first wins). */
+export function unionNativeFeeds(
+  bySender: Record<string, NativeFeed[]> | undefined,
+): NativeFeed[] {
+  if (!bySender) return [];
+  const out: NativeFeed[] = [];
+  const seen = new Set<string>();
+  for (const feeds of Object.values(bySender)) {
+    for (const feed of feeds) {
+      if (seen.has(feed.url)) continue;
+      seen.add(feed.url);
+      out.push({ ...feed });
+    }
+  }
+  return out;
+}

src/types/index.ts

@@ -69,6 +69,13 @@ export interface FeedMetadata {
   pendingConfirmation?: boolean;
 }
 
+// A syndication feed a newsletter advertises about itself (via
+// <link rel="alternate">), as opposed to the KTN-generated feed.
+export interface NativeFeed {
+  url: string;
+  type: "rss" | "atom" | "json";
+}
+
 // Email metadata interface (summary info for listing)
 export interface EmailMetadata {
   key: string;