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,