"""phase43 — plan semantics for inspection_schedules

Extends MT's `inspection_schedules` (phase34) with the single-tenant "plan"
model (ST phase36_scheduled_inspections), rather than adding a second, competing
scheduler table. Adds:

  notes              TEXT      — free-text brief for the inspector
  last_completed_at  DATETIME  — when the last occurrence was fulfilled
  advance_notified   BOOL      — per-occurrence reminder de-dup flags, reset
  due_notified       BOOL        when a recurring schedule rolls forward
  overdue_notified   BOOL
  mode               ENUM      — 'auto'  = cron materialises the Inspection
                                 'plan'  = inspector clicks Start (ST behaviour)

  inspections.inspection_schedule_id  — FK back to the originating schedule

`next_run_at` (phase34) is reused as the due datetime — ST's `next_due_date` by
another name. No duplicate column, no renames (rule 7).

Existing rows keep working exactly as before: `mode` defaults to 'auto', which
is the only behaviour that has ever existed in MT. Nothing flips to 'plan'
unless someone chooses it in the form.

INFORMATION_SCHEMA-guarded throughout — safe to re-run on every tenant DB.
"""

revision      = 'phase43_schedule_plan_fields'
down_revision = 'phase42_area_qr_token'
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 _fk_exists(conn, table, name):
    return conn.execute(sa.text(
        "SELECT COUNT(*) FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS "
        "WHERE TABLE_SCHEMA = DATABASE() AND TABLE_NAME = :t "
        "AND CONSTRAINT_NAME = :n AND CONSTRAINT_TYPE = 'FOREIGN KEY'"
    ), {"t": table, "n": name}).scalar() > 0


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


_NEW_COLUMNS = (
    ('notes',             'TEXT NULL'),
    ('last_completed_at', 'DATETIME NULL'),
    ('advance_notified',  'TINYINT(1) NOT NULL DEFAULT 0'),
    ('due_notified',      'TINYINT(1) NOT NULL DEFAULT 0'),
    ('overdue_notified',  'TINYINT(1) NOT NULL DEFAULT 0'),
    ('mode',              "ENUM('auto','plan') NOT NULL DEFAULT 'auto'"),
)


def upgrade():
    bind = op.get_bind()

    for name, ddl in _NEW_COLUMNS:
        if not _column_exists(bind, 'inspection_schedules', name):
            op.execute(sa.text(
                f"ALTER TABLE inspection_schedules ADD COLUMN {name} {ddl}"
            ))

    # Link a materialised/started Inspection back to its schedule.
    if not _column_exists(bind, 'inspections', 'inspection_schedule_id'):
        op.execute(sa.text(
            "ALTER TABLE inspections ADD COLUMN inspection_schedule_id INT NULL"
        ))
    if not _index_exists(bind, 'inspections', 'ix_inspections_inspection_schedule_id'):
        op.execute(sa.text(
            "CREATE INDEX ix_inspections_inspection_schedule_id "
            "ON inspections (inspection_schedule_id)"
        ))
    if not _fk_exists(bind, 'inspections', 'fk_inspections_inspection_schedule'):
        # ON DELETE SET NULL: deleting a schedule must never delete completed
        # inspection history.
        op.execute(sa.text(
            "ALTER TABLE inspections "
            "ADD CONSTRAINT fk_inspections_inspection_schedule "
            "FOREIGN KEY (inspection_schedule_id) "
            "REFERENCES inspection_schedules (id) ON DELETE SET NULL"
        ))


def downgrade():
    bind = op.get_bind()

    if _fk_exists(bind, 'inspections', 'fk_inspections_inspection_schedule'):
        op.execute(sa.text(
            "ALTER TABLE inspections DROP FOREIGN KEY fk_inspections_inspection_schedule"
        ))
    if _index_exists(bind, 'inspections', 'ix_inspections_inspection_schedule_id'):
        op.execute(sa.text(
            "DROP INDEX ix_inspections_inspection_schedule_id ON inspections"
        ))
    if _column_exists(bind, 'inspections', 'inspection_schedule_id'):
        op.execute(sa.text(
            "ALTER TABLE inspections DROP COLUMN inspection_schedule_id"
        ))

    for name, _ddl in reversed(_NEW_COLUMNS):
        if _column_exists(bind, 'inspection_schedules', name):
            op.execute(sa.text(
                f"ALTER TABLE inspection_schedules DROP COLUMN {name}"
            ))