"""#1197 - 预览生成：generation_tasks 表新增 is_preview 字段

Revision ID: 053
Revises: 052
Create Date: 2026-08-15

Changes:
1. generation_tasks 表新增 is_preview 字段，标记是否为预览生成任务（低清 480p）
2. 默认 False，与现有正式生成任务兼容
3. 加索引以支持按预览/正式任务筛选
"""

import sqlalchemy as sa

from alembic import context, op

revision = "053_generation_task_is_preview"
down_revision = "052_generation_task_bgm_config"
branch_labels = None
depends_on = None


def upgrade() -> None:
    conn = op.get_bind()
    if context.get_context().dialect.name == "postgresql":
        # 检查列是否已存在（幂等）
        result = conn.execute(
            sa.text(
                "SELECT column_name FROM information_schema.columns "
                "WHERE table_name = 'generation_tasks' AND column_name = 'is_preview'"
            )
        )
        if result.scalar() is not None:
            return

    op.add_column(
        "generation_tasks",
        sa.Column("is_preview", sa.Boolean, nullable=False, server_default=sa.text("false")),
    )
    # 加索引
    op.create_index(
        "ix_generation_tasks_is_preview",
        "generation_tasks",
        ["is_preview"],
    )


def downgrade() -> None:
    conn = op.get_bind()
    if context.get_context().dialect.name == "postgresql":
        result = conn.execute(
            sa.text(
                "SELECT column_name FROM information_schema.columns "
                "WHERE table_name = 'generation_tasks' AND column_name = 'is_preview'"
            )
        )
        if result.scalar() is None:
            return

    op.drop_index("ix_generation_tasks_is_preview", table_name="generation_tasks")
    op.drop_column("generation_tasks", "is_preview")