Refactor database connection handling in API endpoints

- Removed direct pool checks and replaced them with a centralized database initialization method in `init_db`.
- Updated API endpoints in `admin.py`, `collection.py`, `pins.py`, and `watched.py` to ensure the database connection pool is initialized before usage.
- Enhanced error handling to raise HTTP exceptions if the database is unavailable.
- Improved the `init_db` function in `database.py` to prevent multiple simultaneous initializations using an asyncio lock.

backend/app/api/pins.py

@@ -3,7 +3,7 @@ from fastapi import APIRouter, HTTPException
 from pydantic import BaseModel
 from typing import Optional
 from uuid import UUID
-from app.core.database import pool
+from app.core.database import init_db, pool as db_pool
 
 router = APIRouter()
 
@@ -16,12 +16,11 @@ class PinCreate(BaseModel):
 @router.get("")
 async def list_pins():
     """List all manual pins"""
-    # Pool should be initialized on startup
-    if not pool:
-        from app.core.database import init_db
-        await init_db()
+    await init_db()
+    if db_pool is None:
+        raise HTTPException(status_code=503, detail="Database not available")
     
-    async with pool.connection() as conn:
+    async with db_pool.connection() as conn:
         async with conn.cursor() as cur:
             query = """
                 SELECT id, country_code, label, pinned_at
@@ -46,12 +45,11 @@ async def list_pins():
 @router.post("")
 async def create_pin(pin: PinCreate):
     """Create a new manual pin"""
-    # Pool should be initialized on startup
-    if not pool:
-        from app.core.database import init_db
-        await init_db()
+    await init_db()
+    if db_pool is None:
+        raise HTTPException(status_code=503, detail="Database not available")
     
-    async with pool.connection() as conn:
+    async with db_pool.connection() as conn:
         async with conn.cursor() as cur:
             query = """
                 INSERT INTO moviemap.manual_pin (country_code, label)
@@ -68,12 +66,11 @@ async def create_pin(pin: PinCreate):
 @router.delete("/{pin_id}")
 async def delete_pin(pin_id: UUID):
     """Delete a manual pin"""
-    # Pool should be initialized on startup
-    if not pool:
-        from app.core.database import init_db
-        await init_db()
+    await init_db()
+    if db_pool is None:
+        raise HTTPException(status_code=503, detail="Database not available")
     
-    async with pool.connection() as conn:
+    async with db_pool.connection() as conn:
         async with conn.cursor() as cur:
             query = "DELETE FROM moviemap.manual_pin WHERE id = %s RETURNING id"
             await cur.execute(query, (str(pin_id),))