"""Add write_mode to identity_sync_targets.

Revision ID: 371
Revises: 370
Create Date: 2026-07-01

The operation dimension of the sync-template matrix (Authing-parity):
``create_update`` (default — the historical behaviour: upsert every
in-scope person), ``create_only`` (link once, never re-touch — the
runner is skipped for anyone Helix has already linked), ``update_only``
(only maintain already-linked people, never create a new downstream
record). Gated centrally in ``_sweep`` on the per-(target,person)
``identity_sync_state.external_id`` link state, so no runner internals
change. ``String(16)`` enum-as-string, NOT NULL, server_default keeps
every existing target on the historical ``create_update`` behaviour.
"""
from __future__ import annotations

import sqlalchemy as sa

from alembic import op

revision = "371"
down_revision = "370"
branch_labels = None
depends_on = None

_TABLE = "identity_sync_targets"
_COL = "write_mode"


def _has_column(bind, table: str, column: str) -> bool:
    return bind.execute(
        sa.text(
            "SELECT 1 FROM information_schema.COLUMNS "
            "WHERE TABLE_SCHEMA = DATABASE() AND TABLE_NAME = :t "
            "AND COLUMN_NAME = :c"
        ),
        {"t": table, "c": column},
    ).scalar() is not None


def upgrade() -> None:
    bind = op.get_bind()
    if not _has_column(bind, _TABLE, _COL):
        op.add_column(
            _TABLE,
            sa.Column(
                _COL,
                sa.String(16),
                nullable=False,
                server_default="create_update",
            ),
        )


def downgrade() -> None:
    bind = op.get_bind()
    if _has_column(bind, _TABLE, _COL):
        op.drop_column(_TABLE, _COL)