"""
轻量级数据库结构迁移

项目没有引入 Alembic，新增列通过幂等的 ALTER TABLE 完成：
先查询 information_schema 判断列是否已存在，不存在才执行 ALTER，
保证多次启动/执行也不会报错或重复加列。
"""
import logging

from sqlalchemy import text

logger = logging.getLogger(__name__)


# (表名, 列名, 建列语句)
CHAT_MESSAGE_COLUMNS = [
    (
        "chat_message",
        "status",
        "ALTER TABLE chat_message ADD COLUMN status VARCHAR(32) NOT NULL DEFAULT 'pending' "
        "COMMENT '消息状态: pending/completed/interrupted/error'",
    ),
    (
        "chat_message",
        "duration_ms",
        "ALTER TABLE chat_message ADD COLUMN duration_ms INT DEFAULT NULL "
        "COMMENT '生成耗时(毫秒)'",
    ),
    (
        "chat_message",
        "thinking_log",
        "ALTER TABLE chat_message ADD COLUMN thinking_log TEXT DEFAULT NULL "
        "COMMENT '思考过程(JSON数组)'",
    ),
]


async def _column_exists(conn, table_name: str, column_name: str) -> bool:
    result = await conn.execute(
        text(
            "SELECT COUNT(*) FROM information_schema.COLUMNS "
            "WHERE TABLE_SCHEMA = DATABASE() "
            "AND TABLE_NAME = :table_name AND COLUMN_NAME = :column_name"
        ),
        {"table_name": table_name, "column_name": column_name},
    )
    return bool(result.scalar())


async def migrate_schema() -> None:
    """为存量数据库补齐新增列。

    只做“新增列”这类非破坏性变更：不修改、不删除、不回填任何已有数据。
    历史消息的中断状态由读取路径（get messages）按旧标记做只读兼容判断。
    """
    from app.core.database import engine

    added = []
    async with engine.begin() as conn:
        for table_name, column_name, ddl in CHAT_MESSAGE_COLUMNS:
            try:
                exists = await _column_exists(conn, table_name, column_name)
            except Exception as exc:  # noqa: BLE001
                logger.warning("检查列 %s.%s 失败，跳过迁移: %s", table_name, column_name, exc)
                return
            if not exists:
                await conn.execute(text(ddl))
                added.append(f"{table_name}.{column_name}")

    if added:
        logger.info("数据库迁移完成，新增列: %s", ", ".join(added))
    else:
        logger.info("数据库结构已是最新，无需迁移")