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

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,