-- +goose Up
-- Hard guarantee against double-booking. The service layer checks for
-- collisions before inserting, but check-then-insert is racy under concurrent
-- requests; these exclusion constraints enforce the same rules atomically.
CREATE EXTENSION IF NOT EXISTS btree_gist;

-- Two appointments may not overlap for the same staff member.
ALTER TABLE bookings
  ADD CONSTRAINT bookings_staff_no_overlap
  EXCLUDE USING gist (
    tenant_id WITH =,
    staff_id WITH =,
    tstzrange(starts_at, ends_at) WITH &&
  ) WHERE (booking_mode = 'appointment' AND status <> 'cancelled' AND staff_id IS NOT NULL);

-- Two appointments may not overlap in the same location.
ALTER TABLE bookings
  ADD CONSTRAINT bookings_location_no_overlap
  EXCLUDE USING gist (
    tenant_id WITH =,
    location_id WITH =,
    tstzrange(starts_at, ends_at) WITH &&
  ) WHERE (booking_mode = 'appointment' AND status <> 'cancelled' AND location_id IS NOT NULL);

-- Appointments with no staff or location assignment occupy the tenant's
-- single implicit resource (mirrors resourcesCollide in the service layer).
ALTER TABLE bookings
  ADD CONSTRAINT bookings_unassigned_no_overlap
  EXCLUDE USING gist (
    tenant_id WITH =,
    tstzrange(starts_at, ends_at) WITH &&
  ) WHERE (booking_mode = 'appointment' AND status <> 'cancelled' AND staff_id IS NULL AND location_id IS NULL);

-- +goose Down
ALTER TABLE bookings DROP CONSTRAINT IF EXISTS bookings_unassigned_no_overlap;
ALTER TABLE bookings DROP CONSTRAINT IF EXISTS bookings_location_no_overlap;
ALTER TABLE bookings DROP CONSTRAINT IF EXISTS bookings_staff_no_overlap;