"""phase47 — scheduled inspection receipt acknowledgement

Adds to `scheduled_inspections`:

    acknowledged_at  DATETIME NULL

When the assigned inspector confirms they have received/seen a scheduled
inspection request. NULL = awaiting confirmation. Reset to NULL by the edit
route when the schedule is reassigned to a different inspector (once per
assignment, not per occurrence). The acknowledger is always the assigned
inspector, so no separate acknowledged_by column is stored.

No backfill: legacy rows keep NULL and render as "awaiting confirmation", which
is the correct initial state for an assignment nobody has confirmed yet.

Uses INFORMATION_SCHEMA check — safe to re-run.
"""

revision      = 'phase47_sched_acknowledged'
down_revision = 'phase46_followup_req_by'
branch_labels = None
depends_on    = None

from alembic import op
import sqlalchemy as sa


def _column_exists(conn, table, column):
    return conn.execute(sa.text(
        "SELECT COUNT(*) FROM INFORMATION_SCHEMA.COLUMNS "
        "WHERE TABLE_SCHEMA = DATABASE() "
        "AND TABLE_NAME = :t AND COLUMN_NAME = :c"
    ), {"t": table, "c": column}).scalar() > 0


def upgrade():
    bind = op.get_bind()
    if not _column_exists(bind, 'scheduled_inspections', 'acknowledged_at'):
        op.execute(sa.text(
            "ALTER TABLE scheduled_inspections ADD COLUMN acknowledged_at DATETIME NULL"
        ))


def downgrade():
    bind = op.get_bind()
    if _column_exists(bind, 'scheduled_inspections', 'acknowledged_at'):
        op.execute(sa.text(
            "ALTER TABLE scheduled_inspections DROP COLUMN acknowledged_at"
        ))