feat: initial commit

backend/app/services/order_service.py

@@ -0,0 +1,22 @@
+"""Order number generation and business logic."""
+from datetime import datetime
+from sqlalchemy.ext.asyncio import AsyncSession
+from sqlalchemy import select, func
+from app.models.order import Order
+
+
+async def generate_order_number(db: AsyncSession) -> str:
+    """Generate next sequential order number: SA-2026-XXXXX."""
+    year = datetime.utcnow().year
+    prefix = f"SA-{year}-"
+
+    # Use MAX to find the highest existing sequence number this year.
+    # COUNT-based approach breaks when orders are deleted (produces duplicates).
+    result = await db.execute(
+        select(func.max(Order.order_number)).where(Order.order_number.like(f"{prefix}%"))
+    )
+    max_num = result.scalar()
+    if max_num:
+        last_seq = int(max_num.split("-")[-1])
+        return f"{prefix}{last_seq + 1:05d}"
+    return f"{prefix}00001"