"""Add content_hash column to files table for SHA-256 dedup and integrity.

Revision ID: 0038_dms_content_hash
Revises: 0037_user_tenant_model
Create Date: 2026-07-25

Changes:
1. Add content_hash (String(64), nullable) column to files table.
"""

from __future__ import annotations

from typing import Union

import sqlalchemy as sa
from alembic import op

# revision identifiers
revision: str = "0038_dms_content_hash"
down_revision: Union[str, None] = "0037_user_tenant_model"
branch_labels: Union[str, None] = None
depends_on: Union[str, None] = None


def _column_exists(table: str, column: str) -> str:
    """Return SQL that checks if a column exists on a table."""
    return (
        f"SELECT 1 FROM information_schema.columns "
        f"WHERE table_name = '{table}' AND column_name = '{column}'"
    )


def upgrade() -> None:
    conn = op.get_bind()
    # Check if table exists first
    table_exists = conn.execute(sa.text("SELECT 1 FROM information_schema.tables WHERE table_name = 'files'")).fetchone()
    if table_exists is None:
        return
    result = conn.execute(sa.text(_column_exists("files", "content_hash"))).fetchone()
    if result is None:
        op.execute("ALTER TABLE files ADD COLUMN IF NOT EXISTS content_hash VARCHAR(64)")


def downgrade() -> None:
    conn = op.get_bind()
    result = conn.execute(sa.text(_column_exists("files", "content_hash"))).fetchone()
    if result is not None:
        op.drop_column("files", "content_hash")