-- migrate:up

-- A bike is normally held for its reservation's own period. These two columns
-- override it for one bike, which is how a conflict is resolved without moving
-- the whole booking: the reservation keeps its hours, and only the bike both
-- bookings want changes hands earlier.
--
-- NULL means "the reservation's period", so every existing row keeps behaving
-- exactly as before.
ALTER TABLE reservations_bikes
    ADD COLUMN start_time timestamptz,
    ADD COLUMN end_time timestamptz;

-- Both or neither, and the right way round
ALTER TABLE reservations_bikes ADD CONSTRAINT reservations_bikes_period CHECK (
    (start_time IS NULL AND end_time IS NULL)
    OR (start_time IS NOT NULL AND end_time IS NOT NULL AND start_time < end_time));

-- Conflicts are looked up by bike — "who else holds this one, and when" — which
-- `reservations_bikes_bike_id_idx` already serves: it was created with the
-- table, and the primary key, starting with reservation_id, could not.

-- migrate:down
ALTER TABLE reservations_bikes DROP CONSTRAINT reservations_bikes_period;
ALTER TABLE reservations_bikes DROP COLUMN start_time, DROP COLUMN end_time;