"""finance_cost_centers.headcount — active-employee count per cost centre.

Revision ID: 303
Revises: 302
Create Date: 2026-06-17

PR1 of the finance closed-loop theme: the authoritative cost-centre master
(``finance_cost_centers``) is no longer populated from 汇联易 alone (which
returns nothing for this app) — a daily reconciler rebuilds it from the
HRIS-synced ``identity_persons.cost_center`` truth. This adds a nullable
``headcount`` column so the reconciler can stamp the active-employee count
per cost centre, letting the coverage UI render "N cost centres / M people"
without a cross-domain join. Idempotent + re-runnable (guards on column
presence so a partial prod apply converges).
"""
from __future__ import annotations

import sqlalchemy as sa

from alembic import op

revision = "303"
down_revision = "302"
branch_labels = None
depends_on = None

TABLE = "finance_cost_centers"
COLUMN = "headcount"


def _column_exists(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 _column_exists(bind, TABLE, COLUMN):
        op.add_column(TABLE, sa.Column(COLUMN, sa.Integer(), nullable=True))


def downgrade() -> None:
    bind = op.get_bind()
    if _column_exists(bind, TABLE, COLUMN):
        op.drop_column(TABLE, COLUMN)