"""bot_channel 的轮询口子要容忍"空字符串"的 GUC

`set_config(..., true)` 提交后会把变量还原成上一次的值；连接池里这条连接如果本来没有
会话级值，还原出来的是空串 `''` 而不是 NULL。`0014` 的策略直接
`current_setting('app.bot_channel', true)::uuid`，空串一 cast 就
`InvalidTextRepresentationError: invalid input syntax for type uuid: ""`，
于是同一连接上下一个请求（比如扫码确认）500。

这里把策略重建成和 `app_ws_id()` 一样的写法：先 `nullif(..., '')` 再 cast。

Revision ID: 0015
Revises: 0014
"""

from __future__ import annotations

from alembic import op

from app.roles import APP_ROLE

revision = "0015"
down_revision = "0014"
branch_labels = None
depends_on = None

STATEMENTS: tuple[str, ...] = (
    "DROP POLICY IF EXISTS bot_channel_worker ON bot_channel",
    """
    CREATE POLICY bot_channel_worker ON bot_channel
    FOR ALL
    USING (
      id = nullif(current_setting('app.bot_channel', true), '')::uuid
    )
    WITH CHECK (
      id = nullif(current_setting('app.bot_channel', true), '')::uuid
    )
    """,
    f"GRANT SELECT, INSERT, UPDATE, DELETE ON bot_channel TO {APP_ROLE}",
)


def upgrade() -> None:
    for statement in STATEMENTS:
        op.execute(statement)


def downgrade() -> None:
    op.execute("DROP POLICY IF EXISTS bot_channel_worker ON bot_channel")
    op.execute(
        """
        CREATE POLICY bot_channel_worker ON bot_channel
        FOR ALL
        USING (id = current_setting('app.bot_channel', true)::uuid)
        WITH CHECK (id = current_setting('app.bot_channel', true)::uuid)
        """
    )