"""16进制自增计数器 — 基于 PostgreSQL Sequence，生成 16 位 HEX 唯一 ID"""
from sqlalchemy import text
from sqlalchemy.ext.asyncio import AsyncSession

SEQUENCE_NAME = "product_hex_counter"


async def ensure_sequence(db: AsyncSession) -> None:
    """确保 counter sequence 存在（幂等）"""
    await db.execute(
        text(f"CREATE SEQUENCE IF NOT EXISTS {SEQUENCE_NAME} START 1;")
    )


async def next_hex_id(db: AsyncSession, length: int = 16) -> str:
    """
    生成下一个 hex ID。

    示例: 1 → "0000000000000001"
          15 → "000000000000000F"
          16 → "0000000000000010"
          255 → "00000000000000FF"
    """
    result = await db.execute(text(f"SELECT nextval('{SEQUENCE_NAME}');"))
    counter: int = result.scalar_one()
    return format(counter, f"0{length}X")