"""#642 - 生成任务新增 bgm_config 字段

Revision ID: 052_generation_task_bgm_config
Revises: 051_generation_task_resolution
Create Date: 2026-07-25

Changes:
1. generation_tasks 表新增 bgm_config 字段（JSON类型），存储用户自定义BGM配置
2. 为空时使用默认空字典

背景：
#642 一键生成支持自定义BGM 功能在 SQLAlchemy 模型中加了 bgm_config 字段，
但遗漏了 alembic migration，导致 staging 环境数据库没有该列，
创建生成任务时直接 500。
"""

import sqlalchemy as sa

from alembic import context, op

revision = "052_generation_task_bgm_config"
down_revision = "051_generation_task_resolution"
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 = 'bgm_config'"
            )
        )
        if result.scalar() is not None:
            return

    op.add_column(
        "generation_tasks",
        sa.Column(
            "bgm_config",
            sa.JSON,
            nullable=False,
            server_default=sa.text("'{}'::json"),
        ),
    )


def downgrade() -> None:
    conn = op.get_bind()
    if context.get_context().dialect.name == "postgresql":
        # 检查列是否存在（幂等）
        result = conn.execute(
            sa.text(
                "SELECT column_name FROM information_schema.columns "
                "WHERE table_name = 'generation_tasks' AND column_name = 'bgm_config'"
            )
        )
        if result.scalar() is None:
            return

    op.drop_column("generation_tasks", "bgm_config")