feat(autopause): pure occupancy-decision function

src/bot/auto-pause.test.ts

@@ -0,0 +1,29 @@
+import { describe, it, expect } from "vitest";
+import { decideOccupancyAction } from "./auto-pause.js";
+
+describe("decideOccupancyAction", () => {
+  it("pauses when empty while playing and enabled", () => {
+    expect(decideOccupancyAction("playing", false, true, 0)).toBe("pause");
+  });
+  it("does not pause when the feature is disabled", () => {
+    expect(decideOccupancyAction("playing", false, false, 0)).toBe("none");
+  });
+  it("does not pause when idle (nothing playing)", () => {
+    expect(decideOccupancyAction("idle", false, true, 0)).toBe("none");
+  });
+  it("does not pause when already paused", () => {
+    expect(decideOccupancyAction("paused", false, true, 0)).toBe("none");
+  });
+  it("resumes when re-populated and we auto-paused", () => {
+    expect(decideOccupancyAction("paused", true, true, 2)).toBe("resume");
+  });
+  it("does NOT resume a user-paused track on re-population", () => {
+    expect(decideOccupancyAction("paused", false, true, 2)).toBe("none");
+  });
+  it("does nothing when re-populated and already playing", () => {
+    expect(decideOccupancyAction("playing", false, true, 2)).toBe("none");
+  });
+  it("resume is independent of the enabled flag (we already auto-paused)", () => {
+    expect(decideOccupancyAction("paused", true, false, 1)).toBe("resume");
+  });
+});

src/bot/auto-pause.ts

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+export type PlayerStateName = "idle" | "playing" | "paused";
+export type OccupancyAction = "pause" | "resume" | "none";
+
+/**
+ * Decide what auto-pause should do given channel occupancy.
+ * - empty (userCount <= 0): pause iff enabled and currently playing.
+ * - re-populated (userCount > 0): resume iff we previously auto-paused and are still paused.
+ * `autoPaused` distinguishes our auto-pause from a user pause, so user pauses are never resumed.
+ */
+export function decideOccupancyAction(
+  playerState: PlayerStateName,
+  autoPaused: boolean,
+  enabled: boolean,
+  userCount: number,
+): OccupancyAction {
+  const empty = userCount <= 0;
+  if (empty) {
+    if (enabled && playerState === "playing") return "pause";
+    return "none";
+  }
+  if (autoPaused && playerState === "paused") return "resume";
+  return "none";
+}