"""phase50 — inspection schedule receipt acknowledgement

Ports single-tenant phase47 onto MT's `inspection_schedules` table. Adds:

    acknowledged_at DATETIME NULL

Stamped when the assigned inspector confirms they have received/seen a scheduled
inspection request. NULL = awaiting confirmation.

Scope of the acknowledgement
----------------------------
It is per ASSIGNMENT, not per occurrence. `fulfill()` and `advance_due_date()`
deliberately leave this column alone as the schedule rolls forward — an
inspector who confirmed "yes, this weekly restroom round is mine" should not be
asked again every week. The edit route resets it to NULL when the schedule is
reassigned to a DIFFERENT inspector, because the new assignee has confirmed
nothing.

The acknowledger is always the assigned inspector — the only person the routes
permit to confirm — so no separate `acknowledged_by` column is stored.

Only meaningful for `plan` mode: an `auto` schedule materialises its inspection
without anyone starting it, so there is no request to receive. The UI shows the
control for plan-mode rows only.

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

Revision id note
----------------
`alembic_version.version_num` is VARCHAR(32); the id below is 24 characters.
The filename stays descriptive — Alembic keys on the `revision` string.

Uses an INFORMATION_SCHEMA check — safe to re-run on every tenant DB. Additive
only: nothing is renamed, retyped or dropped.
"""

revision      = 'phase50_sched_acknowledged'
down_revision = 'phase49_followup_req_by'
branch_labels = None
depends_on    = None

from alembic import op
import sqlalchemy as sa


_TABLE  = 'inspection_schedules'
_COLUMN = 'acknowledged_at'


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


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 _table_exists(bind, _TABLE):
        return
    if not _column_exists(bind, _TABLE, _COLUMN):
        op.execute(sa.text(
            f"ALTER TABLE {_TABLE} ADD COLUMN {_COLUMN} DATETIME NULL"
        ))


def downgrade():
    bind = op.get_bind()
    if not _table_exists(bind, _TABLE):
        return
    if _column_exists(bind, _TABLE, _COLUMN):
        op.execute(sa.text(
            f"ALTER TABLE {_TABLE} DROP COLUMN {_COLUMN}"
        ))