"""Add tenant-local deduplication index on files.

Plan 6.6: Partial unique index on (tenant_id, content_hash)
WHERE content_hash IS NOT NULL AND deleted_at IS NULL.

Before creating the unique index, checks for existing duplicates.

Revision ID: 0098
Revises: 0097
"""

from __future__ import annotations

from alembic import op
import sqlalchemy as sa

revision = "0098"
down_revision = "0097"
branch_labels = None
depends_on = None


def upgrade() -> None:
    # Check for duplicates before creating unique index
    conn = op.get_bind()
    duplicates = conn.execute(
        sa.text(
            "SELECT tenant_id, content_hash, count(*) FROM files "
            "WHERE content_hash IS NOT NULL AND deleted_at IS NULL "
            "GROUP BY tenant_id, content_hash HAVING count(*) > 1"
        )
    ).fetchall()

    if duplicates:
        raise RuntimeError(
            f"Cannot create unique index: {len(duplicates)} duplicate (tenant_id, content_hash) pairs found. "
            "Data cleanup required before migration."
        )

    op.execute(
        "CREATE UNIQUE INDEX IF NOT EXISTS uq_files_tenant_content_hash "
        "ON files (tenant_id, content_hash) "
        "WHERE content_hash IS NOT NULL AND deleted_at IS NULL"
    )


def downgrade() -> None:
    op.execute("DROP INDEX IF EXISTS uq_files_tenant_content_hash")