From 9c273d79fc7615f91c4c8c84c99b027c9e5a2168 Mon Sep 17 00:00:00 2001
From: Huang Xin <chrox.huang@gmail.com>
Date: Mon, 20 Apr 2026 23:57:20 +0800
Subject: [PATCH] fix(tts): fixed race condition on pause/resume, closes #3825
 (#3905)

---
 .../__tests__/services/tts-controller.test.ts | 33 +++++++++++++++++++
 .../src/services/tts/TTSController.ts         |  7 +++-
 2 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/apps/readest-app/src/__tests__/services/tts-controller.test.ts b/apps/readest-app/src/__tests__/services/tts-controller.test.ts
index 1536dd5b..64f89e50 100644
--- a/apps/readest-app/src/__tests__/services/tts-controller.test.ts
+++ b/apps/readest-app/src/__tests__/services/tts-controller.test.ts
@@ -570,6 +570,39 @@ describe('TTSController', () => {
     });
   });
 
+  describe('start', () => {
+    test('uses tts.resume() not tts.start() when state is stopped (play/pause race fix)', async () => {
+      // Repro: `forward()` transitions state to 'stopped' transiently between its
+      // `await this.stop()` and the follow-up navigation. If the user taps play
+      // in that window, `start()` previously called `tts.start()` — which resets
+      // the TTS list to position 0 (section beginning) instead of resuming the
+      // current paragraph. The fix: always use `tts.resume()` (which itself
+      // falls back to `next()` on a fresh TTS), so there's no way `start()`
+      // ever rewinds to the top of a section.
+      await controller.initViewTTS(0);
+
+      const ttsStartMock = vi.fn().mockReturnValue('<speak>section-start</speak>');
+      const ttsResumeMock = vi.fn().mockReturnValue('<speak>current</speak>');
+      const tts = mockView.tts as unknown as {
+        start: typeof ttsStartMock;
+        resume: typeof ttsResumeMock;
+        next: ReturnType<typeof vi.fn>;
+        prev: ReturnType<typeof vi.fn>;
+      };
+      tts.start = ttsStartMock;
+      tts.resume = ttsResumeMock;
+      tts.next = vi.fn().mockReturnValue(undefined);
+      tts.prev = vi.fn();
+
+      // Simulate the race: state is 'stopped' (transient during forward())
+      controller.state = 'stopped';
+      await controller.start();
+
+      expect(ttsResumeMock).toHaveBeenCalled();
+      expect(ttsStartMock).not.toHaveBeenCalled();
+    });
+  });
+
   describe('forward and backward', () => {
     test('forward sets forward-paused state when not playing', async () => {
       // Set up controller with a mock tts on the view
diff --git a/apps/readest-app/src/services/tts/TTSController.ts b/apps/readest-app/src/services/tts/TTSController.ts
index bb179293..d19ce1d2 100644
--- a/apps/readest-app/src/services/tts/TTSController.ts
+++ b/apps/readest-app/src/services/tts/TTSController.ts
@@ -407,7 +407,12 @@ export class TTSController extends EventTarget {
 
   async start() {
     await this.initViewTTS();
-    const ssml = this.state.includes('paused') ? this.view.tts?.resume() : this.view.tts?.start();
+    // Always resume from the current list position instead of calling tts.start().
+    // tts.start() resets the TTS list to position 0 (section beginning), which is
+    // wrong when state transiently becomes 'stopped' during forward()/backward()
+    // — a fast play tap in that window would otherwise jump back to section start.
+    // tts.resume() falls back to tts.next() on a fresh TTS, so it's safe at init.
+    const ssml = this.view.tts?.resume();
     if (this.state.includes('paused')) {
       this.resume();
     }