"""story_image_intents: one primary per story + optional FK to assets

Revision ID: 0009_si_constraints
Revises: 0008_legacy_assets
"""

from typing import Sequence, Union

import sqlalchemy as sa
from alembic import op

revision: str = "0009_si_constraints"
down_revision: Union[str, Sequence[str], None] = "0008_legacy_assets"
branch_labels: Union[str, Sequence[str], None] = None
depends_on: Union[str, Sequence[str], None] = None


def upgrade() -> None:
    bind = op.get_bind()
    bind.execute(
        sa.text(
            """
            UPDATE story_image_intents SET asset_id = NULL
            WHERE asset_id IS NOT NULL
              AND NOT EXISTS (SELECT 1 FROM assets a WHERE a.id = story_image_intents.asset_id)
            """
        )
    )
    # 去重：同一 story 多条 primary 时保留最新一条
    bind.execute(
        sa.text(
            """
            DELETE FROM story_image_intents
            WHERE id IN (
              SELECT id FROM (
                SELECT id,
                  ROW_NUMBER() OVER (
                    PARTITION BY story_id
                    ORDER BY created_at DESC NULLS LAST, id DESC
                  ) AS rn
                FROM story_image_intents
                WHERE intent_role = 'primary'
              ) t
              WHERE rn > 1
            )
            """
        )
    )
    op.create_foreign_key(
        "fk_story_image_intents_asset_id_assets",
        "story_image_intents",
        "assets",
        ["asset_id"],
        ["id"],
        ondelete="SET NULL",
    )
    op.execute(
        """
        CREATE UNIQUE INDEX IF NOT EXISTS uq_story_primary_image_intent
        ON story_image_intents (story_id)
        WHERE intent_role = 'primary'
        """
    )


def downgrade() -> None:
    op.execute("DROP INDEX IF EXISTS uq_story_primary_image_intent")
    op.drop_constraint(
        "fk_story_image_intents_asset_id_assets",
        "story_image_intents",
        type_="foreignkey",
    )