feat: Add position shifting logic for adding sounds to playlists in repository

app/repositories/playlist.py

@@ -1,7 +1,7 @@
 """Playlist repository for database operations."""
 
 from enum import Enum
-from sqlalchemy import func
+from sqlalchemy import func, update
 from sqlalchemy.orm import selectinload
 from sqlmodel import col, select
 from sqlmodel.ext.asyncio.session import AsyncSession
@@ -120,6 +120,20 @@ class PlaylistRepository(BaseRepository[Playlist]):
             logger.exception("Failed to get sounds for playlist: %s", playlist_id)
             raise
 
+    async def get_playlist_sound_entries(self, playlist_id: int) -> list[PlaylistSound]:
+        """Get all PlaylistSound entries for a playlist, ordered by position."""
+        try:
+            statement = (
+                select(PlaylistSound)
+                .where(PlaylistSound.playlist_id == playlist_id)
+                .order_by(PlaylistSound.position)
+            )
+            result = await self.session.exec(statement)
+            return list(result.all())
+        except Exception:
+            logger.exception("Failed to get playlist sound entries for playlist: %s", playlist_id)
+            raise
+
     async def add_sound_to_playlist(
         self,
         playlist_id: int,
@@ -135,6 +149,35 @@ class PlaylistRepository(BaseRepository[Playlist]):
                 ).where(PlaylistSound.playlist_id == playlist_id)
                 result = await self.session.exec(statement)
                 position = result.first() or 0
+            else:
+                # Shift existing positions to make room for the new sound
+                # Use a two-step approach to avoid unique constraint violations:
+                # 1. Move all affected positions to negative temporary positions
+                # 2. Then move them to their final positions
+                
+                # Step 1: Move to temporary negative positions
+                update_to_negative = (
+                    update(PlaylistSound)
+                    .where(
+                        PlaylistSound.playlist_id == playlist_id,
+                        PlaylistSound.position >= position,
+                    )
+                    .values(position=PlaylistSound.position - 10000)
+                )
+                await self.session.exec(update_to_negative)
+                await self.session.commit()
+                
+                # Step 2: Move from temporary negative positions to final positions  
+                update_to_final = (
+                    update(PlaylistSound)
+                    .where(
+                        PlaylistSound.playlist_id == playlist_id,
+                        PlaylistSound.position < 0,
+                    )
+                    .values(position=PlaylistSound.position + 10001)
+                )
+                await self.session.exec(update_to_final)
+                await self.session.commit()
 
             playlist_sound = PlaylistSound(
                 playlist_id=playlist_id,

tests/repositories/test_playlist.py

@@ -480,6 +480,158 @@ class TestPlaylistRepository:
 
         assert playlist_sound.position == TEST_POSITION
 
+    @pytest.mark.asyncio
+    async def test_add_sound_to_playlist_with_position_shifting(
+        self,
+        playlist_repository: PlaylistRepository,
+        test_session: AsyncSession,
+        ensure_plans: Any,
+    ) -> None:
+        """Test adding a sound to a playlist with position shifting when positions are occupied."""
+        # Create test user
+        user = User(
+            email="test_shifting@example.com",
+            name="Test User Shifting",
+            password_hash=PasswordUtils.hash_password("password123"),
+            role="user",
+            is_active=True,
+            plan_id=ensure_plans[0].id,
+            credits=100,
+        )
+        test_session.add(user)
+        await test_session.commit()
+        await test_session.refresh(user)
+        user_id = user.id
+
+        # Create test playlist
+        playlist = Playlist(
+            user_id=user_id,
+            name="Test Playlist Shifting",
+            description="A test playlist for position shifting",
+            genre="test",
+            is_main=False,
+            is_current=False,
+            is_deletable=True,
+        )
+        test_session.add(playlist)
+
+        # Create multiple sounds
+        sounds = []
+        for i in range(3):
+            sound = Sound(
+                name=f"Test Sound {i}",
+                filename=f"test_{i}.mp3",
+                type="SDB",
+                duration=5000,
+                size=1024,
+                hash=f"test_hash_{i}",
+                play_count=0,
+            )
+            test_session.add(sound)
+            sounds.append(sound)
+        
+        await test_session.commit()
+        await test_session.refresh(playlist)
+        for sound in sounds:
+            await test_session.refresh(sound)
+
+        playlist_id = playlist.id
+        sound_ids = [s.id for s in sounds]
+
+        # Add first two sounds sequentially (positions 0, 1)
+        await playlist_repository.add_sound_to_playlist(playlist_id, sound_ids[0])  # position 0
+        await playlist_repository.add_sound_to_playlist(playlist_id, sound_ids[1])  # position 1
+
+        # Now insert third sound at position 1 - should shift existing sound at position 1 to position 2
+        await playlist_repository.add_sound_to_playlist(playlist_id, sound_ids[2], position=1)
+
+        # Verify the final positions
+        playlist_sounds = await playlist_repository.get_playlist_sound_entries(playlist_id)
+        
+        assert len(playlist_sounds) == 3
+        assert playlist_sounds[0].sound_id == sound_ids[0]  # Original sound 0 stays at position 0
+        assert playlist_sounds[0].position == 0
+        assert playlist_sounds[1].sound_id == sound_ids[2]  # New sound 2 inserted at position 1
+        assert playlist_sounds[1].position == 1
+        assert playlist_sounds[2].sound_id == sound_ids[1]  # Original sound 1 shifted to position 2
+        assert playlist_sounds[2].position == 2
+
+    @pytest.mark.asyncio
+    async def test_add_sound_to_playlist_at_position_zero(
+        self,
+        playlist_repository: PlaylistRepository,
+        test_session: AsyncSession,
+        ensure_plans: Any,
+    ) -> None:
+        """Test adding a sound at position 0 when playlist already has sounds."""
+        # Create test user
+        user = User(
+            email="test_position_zero@example.com",
+            name="Test User Position Zero",
+            password_hash=PasswordUtils.hash_password("password123"),
+            role="user",
+            is_active=True,
+            plan_id=ensure_plans[0].id,
+            credits=100,
+        )
+        test_session.add(user)
+        await test_session.commit()
+        await test_session.refresh(user)
+        user_id = user.id
+
+        # Create test playlist
+        playlist = Playlist(
+            user_id=user_id,
+            name="Test Playlist Position Zero",
+            description="A test playlist for position zero insertion",
+            genre="test",
+            is_main=False,
+            is_current=False,
+            is_deletable=True,
+        )
+        test_session.add(playlist)
+
+        # Create multiple sounds
+        sounds = []
+        for i in range(3):
+            sound = Sound(
+                name=f"Test Sound {i}",
+                filename=f"test_zero_{i}.mp3",
+                type="SDB",
+                duration=5000,
+                size=1024,
+                hash=f"test_hash_zero_{i}",
+                play_count=0,
+            )
+            test_session.add(sound)
+            sounds.append(sound)
+        
+        await test_session.commit()
+        await test_session.refresh(playlist)
+        for sound in sounds:
+            await test_session.refresh(sound)
+
+        playlist_id = playlist.id
+        sound_ids = [s.id for s in sounds]
+
+        # Add first two sounds sequentially (positions 0, 1)
+        await playlist_repository.add_sound_to_playlist(playlist_id, sound_ids[0])  # position 0
+        await playlist_repository.add_sound_to_playlist(playlist_id, sound_ids[1])  # position 1
+
+        # Now insert third sound at position 0 - should shift existing sounds to positions 1, 2
+        await playlist_repository.add_sound_to_playlist(playlist_id, sound_ids[2], position=0)
+
+        # Verify the final positions
+        playlist_sounds = await playlist_repository.get_playlist_sound_entries(playlist_id)
+        
+        assert len(playlist_sounds) == 3
+        assert playlist_sounds[0].sound_id == sound_ids[2]  # New sound 2 inserted at position 0
+        assert playlist_sounds[0].position == 0
+        assert playlist_sounds[1].sound_id == sound_ids[0]  # Original sound 0 shifted to position 1
+        assert playlist_sounds[1].position == 1
+        assert playlist_sounds[2].sound_id == sound_ids[1]  # Original sound 1 shifted to position 2
+        assert playlist_sounds[2].position == 2
+
     @pytest.mark.asyncio
     async def test_remove_sound_from_playlist(
         self,