feat(casting): add CastSelection model and resolution helpers

utils/casting/selection.test.ts

@@ -0,0 +1,88 @@
+import { describe, expect, test } from "bun:test";
+import type { BaseItemDto } from "@jellyfin/sdk/lib/generated-client";
+import {
+  resolveDefaultAudioIndex,
+  resolveSelection,
+  selectionsEqual,
+} from "./selection";
+
+const item: BaseItemDto = {
+  Id: "item-1",
+  MediaSources: [
+    {
+      Id: "src-a",
+      DefaultAudioStreamIndex: 2,
+      DefaultSubtitleStreamIndex: 3,
+      MediaStreams: [
+        { Type: "Video", Index: 0 },
+        { Type: "Audio", Index: 1, IsDefault: false },
+        { Type: "Audio", Index: 2, IsDefault: true },
+        { Type: "Subtitle", Index: 3 },
+      ],
+    },
+    {
+      Id: "src-b",
+      MediaStreams: [
+        { Type: "Video", Index: 0 },
+        { Type: "Audio", Index: 1, IsDefault: false },
+      ],
+    },
+  ],
+};
+
+describe("resolveDefaultAudioIndex", () => {
+  test("uses the source's DefaultAudioStreamIndex when present", () => {
+    expect(resolveDefaultAudioIndex(item, "src-a")).toBe(2);
+  });
+
+  test("falls back to the first audio stream when no default flag", () => {
+    expect(resolveDefaultAudioIndex(item, "src-b")).toBe(1);
+  });
+});
+
+describe("resolveSelection", () => {
+  test("fills every field from server defaults of the first source", () => {
+    const sel = resolveSelection(item, {});
+    expect(sel.mediaSourceId).toBe("src-a");
+    expect(sel.audioStreamIndex).toBe(2);
+    expect(sel.subtitleStreamIndex).toBe(3);
+    expect(sel.maxBitrate).toBeUndefined();
+  });
+
+  test("a partial overrides defaults and keeps the rest", () => {
+    const sel = resolveSelection(item, {
+      audioStreamIndex: 1,
+      maxBitrate: 4_000_000,
+    });
+    expect(sel.audioStreamIndex).toBe(1);
+    expect(sel.maxBitrate).toBe(4_000_000);
+    expect(sel.subtitleStreamIndex).toBe(3);
+  });
+
+  test("switching version resolves that version's defaults", () => {
+    const sel = resolveSelection(item, { mediaSourceId: "src-b" });
+    expect(sel.mediaSourceId).toBe("src-b");
+    expect(sel.audioStreamIndex).toBe(1);
+    expect(sel.subtitleStreamIndex).toBe(-1);
+  });
+});
+
+describe("selectionsEqual", () => {
+  test("true for identical selections", () => {
+    const a = {
+      mediaSourceId: "s",
+      audioStreamIndex: 1,
+      subtitleStreamIndex: -1,
+    };
+    expect(selectionsEqual(a, { ...a })).toBe(true);
+  });
+
+  test("false when any field differs", () => {
+    const a = {
+      mediaSourceId: "s",
+      audioStreamIndex: 1,
+      subtitleStreamIndex: -1,
+    };
+    expect(selectionsEqual(a, { ...a, audioStreamIndex: 2 })).toBe(false);
+  });
+});