test: resolveUserThemePreference unit and resolveTheme integration tests

apps/web/src/lib/__tests__/theme-resolution.test.ts

···
 import {
   detectColorScheme,
   parseRkeyFromUri,
+  resolveUserThemePreference,
   FALLBACK_THEME,
   fallbackForScheme,
   resolveTheme,
···
 
   it("returns null for empty string", () => {
     expect(parseRkeyFromUri("")).toBeNull();
+  });
+});
+
+describe("resolveUserThemePreference", () => {
+  const availableThemes = [
+    { uri: "at://did:plc:forum/space.atbb.forum.theme/3lbllight" },
+    { uri: "at://did:plc:forum/space.atbb.forum.theme/3lbldark" },
+  ];
+
+  it("returns null when allowUserChoice is false", () => {
+    const result = resolveUserThemePreference(
+      "atbb-light-theme=at://did:plc:forum/space.atbb.forum.theme/3lbllight",
+      "light",
+      availableThemes,
+      false
+    );
+    expect(result).toBeNull();
+  });
+
+  it("returns atbb-light-theme URI when cookie matches and is in availableThemes", () => {
+    const result = resolveUserThemePreference(
+      "atbb-light-theme=at://did:plc:forum/space.atbb.forum.theme/3lbllight",
+      "light",
+      availableThemes,
+      true
+    );
+    expect(result).toBe("at://did:plc:forum/space.atbb.forum.theme/3lbllight");
+  });
+
+  it("returns atbb-dark-theme URI when cookie matches and is in availableThemes", () => {
+    const result = resolveUserThemePreference(
+      "atbb-dark-theme=at://did:plc:forum/space.atbb.forum.theme/3lbldark",
+      "dark",
+      availableThemes,
+      true
+    );
+    expect(result).toBe("at://did:plc:forum/space.atbb.forum.theme/3lbldark");
+  });
+
+  it("returns null when cookie URI is not in availableThemes (stale/removed)", () => {
+    const result = resolveUserThemePreference(
+      "atbb-light-theme=at://did:plc:forum/space.atbb.forum.theme/stale",
+      "light",
+      availableThemes,
+      true
+    );
+    expect(result).toBeNull();
+  });
+
+  it("returns null when cookieHeader is undefined", () => {
+    const result = resolveUserThemePreference(
+      undefined,
+      "light",
+      availableThemes,
+      true
+    );
+    expect(result).toBeNull();
+  });
+
+  it("returns null when cookie value is empty string after cookie name", () => {
+    const result = resolveUserThemePreference(
+      "atbb-light-theme=",
+      "light",
+      availableThemes,
+      true
+    );
+    expect(result).toBeNull();
+  });
+
+  it("does not match x-atbb-light-theme as a cookie prefix", () => {
+    const result = resolveUserThemePreference(
+      "x-atbb-light-theme=at://did:plc:forum/space.atbb.forum.theme/3lbllight",
+      "light",
+      availableThemes,
+      true
+    );
+    expect(result).toBeNull();
   });
 });
 
···
       expect.stringContaining("CID mismatch"),
       expect.any(Object)
     );
+  });
+
+  it("resolves light preference cookie when URI is in availableThemes", async () => {
+    mockFetch
+      .mockResolvedValueOnce(policyResponse())
+      .mockResolvedValueOnce(themeResponse("light", "bafylight"));
+
+    const cookieHeader = "atbb-light-theme=at://did:plc:forum/space.atbb.forum.theme/3lbllight";
+    const result = await resolveTheme(APPVIEW, cookieHeader, undefined);
+
+    expect(result.tokens["color-bg"]).toBe("#fff");
+    expect(result.colorScheme).toBe("light");
+    // Verify that the user's theme was fetched (rkey 3lbllight) not the forum default
+    expect(mockFetch).toHaveBeenCalledWith(expect.stringContaining("3lbllight"));
+  });
+
+  it("resolves dark preference cookie when URI is in availableThemes", async () => {
+    mockFetch
+      .mockResolvedValueOnce(policyResponse())
+      .mockResolvedValueOnce(themeResponse("dark", "bafydark"));
+
+    const cookieHeader = "atbb-color-scheme=dark; atbb-dark-theme=at://did:plc:forum/space.atbb.forum.theme/3lbldark";
+    const result = await resolveTheme(APPVIEW, cookieHeader, undefined);
+
+    expect(result.tokens["color-bg"]).toBe("#111");
+    expect(result.colorScheme).toBe("dark");
+    // Verify that the user's theme was fetched (rkey 3lbldark)
+    expect(mockFetch).toHaveBeenCalledWith(expect.stringContaining("3lbldark"));
+  });
+
+  it("falls back to forum default when preference cookie URI is not in availableThemes", async () => {
+    mockFetch
+      .mockResolvedValueOnce(policyResponse())
+      .mockResolvedValueOnce(themeResponse("light", "bafylight"));
+
+    const cookieHeader = "atbb-color-scheme=light; atbb-light-theme=at://did:plc:forum/space.atbb.forum.theme/stale-uri";
+    const result = await resolveTheme(APPVIEW, cookieHeader, undefined);
+
+    // Preference URI is stale, so forum default is used
+    expect(result.tokens["color-bg"]).toBe("#fff");
+    expect(mockFetch).toHaveBeenCalledWith(expect.stringContaining("3lbllight")); // forum default rkey
+  });
+
+  it("ignores preference cookie when policy has allowUserChoice: false", async () => {
+    mockFetch
+      .mockResolvedValueOnce(policyResponse({ allowUserChoice: false }))
+      .mockResolvedValueOnce(themeResponse("light", "bafylight"));
+
+    const cookieHeader = "atbb-color-scheme=light; atbb-light-theme=at://did:plc:forum/space.atbb.forum.theme/stale";
+    const result = await resolveTheme(APPVIEW, cookieHeader, undefined);
+
+    // User choice is disabled, so forum default is used even though cookie is set
+    expect(result.tokens["color-bg"]).toBe("#fff");
+    expect(mockFetch).toHaveBeenCalledWith(expect.stringContaining("3lbllight")); // forum default rkey
   });
 });