"""2026070902_add_generated_date_expression_indexes

Revision ID: 2026070902
Revises: 2026070901
Create Date: 2026-07-09 00:00:00.000000

该文件包含 2026-07-09 的数据库迁移内容：
1. chat_generation_tasks 表增加 generated_at 日期表达式索引，优化按日期分组/筛选
2. generation_records 表增加 generated_at 日期表达式索引，优化按日期分组/筛选
"""
from typing import Sequence, Union

from alembic import op
import sqlalchemy as sa


revision: str = '2026070902'
down_revision: Union[str, None] = '2026070901'
branch_labels: Union[str, Sequence[str], None] = None
depends_on: Union[str, Sequence[str], None] = None


def upgrade() -> None:
    # ========================================
    # 2026-07-09 - 生成记录表增加日期表达式索引
    # ========================================
    # 使用 CAST(timezone('utc', generated_at) AS date) 而不是 date(generated_at)：
    # 1) 当 generated_at 为 timestamptz 时，date() 的结果依赖会话时区，属于 STABLE 函数，
    #    无法用于索引表达式。显式指定 UTC 时区后转为 date 是纯计算，属于 IMMUTABLE。
    # 2) 必须用 CAST(... AS date) 而不能用 ::date：:: 的优先级高于函数调用，
    #    PG 会把 func(x)::date 解析为 func(x::date)，导致语法错误。
    op.create_index(
        'idx_chat_generation_tasks_generated_date',
        'chat_generation_tasks',
        [sa.text("CAST(timezone('utc', generated_at) AS date)")],
        unique=False,
    )
    op.create_index(
        'idx_generation_records_generated_date',
        'generation_records',
        [sa.text("CAST(timezone('utc', generated_at) AS date)")],
        unique=False,
    )


def downgrade() -> None:
    # ========================================
    # 2026-07-09 - 生成记录表增加日期表达式索引（回滚）
    # ========================================
    op.drop_index('idx_generation_records_generated_date', table_name='generation_records')
    op.drop_index('idx_chat_generation_tasks_generated_date', table_name='chat_generation_tasks')