Task 19: Update TTS generation endpoint to accept edited scripts

- Modified TTSRequest to accept optional segments array
- Updated generate_audiobook endpoint to use segments if provided
- Added generate_audiobook_from_segments method to TTSService
- Ensured backward compatibility with text-based generation
- Added comprehensive tests for segment-based generation
- All tests passing (7/7)

Requirements: 15.7

backend/main.py

@@ -56,7 +56,8 @@ class RoleVoiceMapping(BaseModel):
 
 class TTSRequest(BaseModel):
     """Request model for TTS generation endpoint."""
-    text: str = Field(..., description="Text to convert to speech")
+    segments: Optional[List[ScriptSegment]] = Field(None, description="Optional edited script segments")
+    text: Optional[str] = Field(None, description="Text to convert to speech (used if segments not provided)")
     lang: str = Field(..., description="Language code (a, b, f, j)")
     roles: List[RoleVoiceMapping] = Field(..., description="Role to voice mappings")
     speed: Optional[float] = Field(1.0, description="Playback speed (0.5-1.5)")
@@ -253,11 +254,24 @@ async def generate_audiobook(request: TTSRequest):
     """
     logger.info(
         f"Audio generation requested: lang={request.lang}, "
-        f"roles={len(request.roles)}, speed={request.speed}"
+        f"roles={len(request.roles)}, speed={request.speed}, "
+        f"segments={len(request.segments) if request.segments else 0}"
     )
     
-    # Validate required fields (Pydantic handles basic validation)
-    if not request.text or not request.text.strip():
+    # Validate that either segments or text is provided
+    if not request.segments and not request.text:
+        logger.error("Neither segments nor text provided")
+        return JSONResponse(
+            status_code=status.HTTP_400_BAD_REQUEST,
+            content={
+                "error": "ValidationError",
+                "message": "Either segments or text must be provided",
+                "details": {"fields": ["segments", "text"]}
+            }
+        )
+    
+    # Validate text if provided and no segments
+    if not request.segments and request.text and not request.text.strip():
         logger.error("Empty text provided")
         return JSONResponse(
             status_code=status.HTTP_400_BAD_REQUEST,
@@ -316,13 +330,23 @@ async def generate_audiobook(request: TTSRequest):
     role_voice_map = {role.id: role.voice for role in request.roles}
     
     try:
-        # Generate audiobook
-        audio_bytes = await tts_service.generate_audiobook(
-            text=request.text,
-            lang=request.lang,
-            role_voice_map=role_voice_map,
-            speed=request.speed
-        )
+        # Generate audiobook using segments if provided, otherwise use text
+        if request.segments:
+            logger.info(f"Generating audiobook from {len(request.segments)} edited segments")
+            audio_bytes = await tts_service.generate_audiobook_from_segments(
+                segments=[(seg.speaker, seg.text) for seg in request.segments],
+                lang=request.lang,
+                role_voice_map=role_voice_map,
+                speed=request.speed
+            )
+        else:
+            logger.info("Generating audiobook from text with automatic segmentation")
+            audio_bytes = await tts_service.generate_audiobook(
+                text=request.text,
+                lang=request.lang,
+                role_voice_map=role_voice_map,
+                speed=request.speed
+            )
         
         # Create streaming response with proper headers
         return StreamingResponse(

backend/services/tts_service.py

@@ -404,3 +404,66 @@ class TTSService:
         
         logger.info(f"Generated audiobook: {len(audio_bytes)} bytes")
         return audio_bytes
+
+    async def generate_audiobook_from_segments(
+        self,
+        segments: List[Tuple[str, str]],
+        lang: str,
+        role_voice_map: Dict[str, str],
+        speed: float = 1.0
+    ) -> bytes:
+        """
+        Generates audiobook from pre-segmented script with speaker assignments.
+        
+        This method is used when the user has reviewed and edited the script,
+        bypassing automatic segmentation.
+        
+        Args:
+            segments: List of (speaker_name, text_content) tuples
+            lang: Language code
+            role_voice_map: Role to voice ID mapping
+            speed: Playback speed
+            
+        Returns:
+            Audio data as bytes (WAV format)
+            
+        Raises:
+            ValueError: If segments is empty or invalid
+        """
+        logger.info(
+            f"Generating audiobook from {len(segments)} edited segments: "
+            f"lang={lang}, speed={speed}, roles={len(role_voice_map)}"
+        )
+        
+        if not segments:
+            raise ValueError("No segments provided for synthesis")
+        
+        # Get or create pipeline for language
+        pipeline = self.get_pipeline(lang)
+        
+        # Convert segments to format with voice assignments
+        segments_with_voice = []
+        for speaker, text in segments:
+            voice = role_voice_map.get(speaker, self.DEFAULT_VOICE)
+            segments_with_voice.append((speaker, voice, text))
+        
+        logger.info(f"Processing {len(segments_with_voice)} segments with voice assignments")
+        
+        # Synthesize each segment
+        audio_segments = []
+        for role_id, voice, content in segments_with_voice:
+            logger.debug(f"Synthesizing segment for role '{role_id}' with voice '{voice}'")
+            audio = self.synthesize_segment(pipeline, content, voice, speed)
+            audio_segments.append(audio)
+        
+        # Concatenate all audio
+        final_audio = self.concatenate_audio(audio_segments)
+        
+        # Convert to bytes (WAV format)
+        buffer = io.BytesIO()
+        sf.write(buffer, final_audio, self.SAMPLE_RATE, format='WAV')
+        buffer.seek(0)
+        audio_bytes = buffer.read()
+        
+        logger.info(f"Generated audiobook from edited segments: {len(audio_bytes)} bytes")
+        return audio_bytes

backend/test_segment_based_generation.py

@@ -0,0 +1,164 @@
+"""
+Test for segment-based audiobook generation (Task 19).
+
+Tests that the TTS endpoint can accept edited script segments
+and generate audio from them, while maintaining backward compatibility
+with text-based generation.
+"""
+import pytest
+from fastapi.testclient import TestClient
+from main import app
+
+client = TestClient(app)
+
+
+def test_generate_audiobook_with_segments():
+    """Test that audiobook can be generated from edited script segments."""
+    # Prepare request with segments
+    request_data = {
+        "segments": [
+            {"id": "seg_0", "speaker": "Alice", "text": "Hello, how are you?"},
+            {"id": "seg_1", "speaker": "Bob", "text": "I'm doing great, thanks!"},
+            {"id": "seg_2", "speaker": "Narrator", "text": "They continued their conversation."}
+        ],
+        "lang": "a",
+        "roles": [
+            {"id": "Alice", "voice": "af_bella"},
+            {"id": "Bob", "voice": "am_adam"},
+            {"id": "Narrator", "voice": "af_sarah"}
+        ],
+        "speed": 1.0
+    }
+    
+    response = client.post("/api/tts", json=request_data)
+    
+    # Should succeed
+    assert response.status_code == 200
+    assert response.headers["content-type"] == "audio/wav"
+    assert "audiobook.wav" in response.headers.get("content-disposition", "")
+    assert len(response.content) > 0
+
+
+def test_generate_audiobook_with_text_backward_compatibility():
+    """Test that audiobook generation still works with text (backward compatibility)."""
+    # Prepare request with text (old format)
+    request_data = {
+        "text": "Alice: Hello there!\nBob: Hi Alice!",
+        "lang": "a",
+        "roles": [
+            {"id": "Alice", "voice": "af_bella"},
+            {"id": "Bob", "voice": "am_adam"}
+        ],
+        "speed": 1.0
+    }
+    
+    response = client.post("/api/tts", json=request_data)
+    
+    # Should succeed
+    assert response.status_code == 200
+    assert response.headers["content-type"] == "audio/wav"
+    assert len(response.content) > 0
+
+
+def test_generate_audiobook_segments_take_precedence():
+    """Test that segments are used when both segments and text are provided."""
+    # Prepare request with both segments and text
+    request_data = {
+        "segments": [
+            {"id": "seg_0", "speaker": "Alice", "text": "From segments"}
+        ],
+        "text": "Alice: From text",
+        "lang": "a",
+        "roles": [
+            {"id": "Alice", "voice": "af_bella"}
+        ],
+        "speed": 1.0
+    }
+    
+    response = client.post("/api/tts", json=request_data)
+    
+    # Should succeed and use segments
+    assert response.status_code == 200
+    assert response.headers["content-type"] == "audio/wav"
+
+
+def test_generate_audiobook_missing_both_segments_and_text():
+    """Test that request fails when neither segments nor text is provided."""
+    request_data = {
+        "lang": "a",
+        "roles": [
+            {"id": "Alice", "voice": "af_bella"}
+        ],
+        "speed": 1.0
+    }
+    
+    response = client.post("/api/tts", json=request_data)
+    
+    # Should fail with validation error
+    assert response.status_code == 400
+    assert "ValidationError" in response.json()["error"]
+
+
+def test_generate_audiobook_empty_segments():
+    """Test that request fails when segments array is empty."""
+    request_data = {
+        "segments": [],
+        "lang": "a",
+        "roles": [
+            {"id": "Alice", "voice": "af_bella"}
+        ],
+        "speed": 1.0
+    }
+    
+    response = client.post("/api/tts", json=request_data)
+    
+    # Should fail - empty segments should be treated as not provided
+    assert response.status_code == 400
+
+
+def test_edited_script_preserves_speaker_assignments():
+    """Test that edited speaker assignments in segments are preserved."""
+    # Segments where user has changed speaker assignments
+    request_data = {
+        "segments": [
+            {"id": "seg_0", "speaker": "Bob", "text": "This was originally Alice's line"},
+            {"id": "seg_1", "speaker": "Alice", "text": "This was originally Bob's line"}
+        ],
+        "lang": "a",
+        "roles": [
+            {"id": "Alice", "voice": "af_bella"},
+            {"id": "Bob", "voice": "am_adam"}
+        ],
+        "speed": 1.0
+    }
+    
+    response = client.post("/api/tts", json=request_data)
+    
+    # Should succeed with edited assignments
+    assert response.status_code == 200
+    assert response.headers["content-type"] == "audio/wav"
+    assert len(response.content) > 0
+
+
+def test_segment_with_unmapped_speaker_uses_default():
+    """Test that segments with unmapped speakers fall back to default voice."""
+    request_data = {
+        "segments": [
+            {"id": "seg_0", "speaker": "UnknownSpeaker", "text": "Hello from unknown"}
+        ],
+        "lang": "a",
+        "roles": [
+            {"id": "Alice", "voice": "af_bella"}
+        ],
+        "speed": 1.0
+    }
+    
+    response = client.post("/api/tts", json=request_data)
+    
+    # Should succeed using default voice
+    assert response.status_code == 200
+    assert response.headers["content-type"] == "audio/wav"
+
+
+if __name__ == "__main__":
+    pytest.main([__file__, "-v"])