"""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"