BEGIN;

-- Replaces the boolean processed/processed_successfully pair with a
-- three-state model driven by two nullable timestamps:
--   unprocessed: notified_at IS NULL
--   notified:    notified_at IS NOT NULL AND processed_at IS NULL
--   processed:   processed_at IS NOT NULL
-- The dispatcher sets notified_at each time it hands an event to the
-- listener (initially, and again on retry if the listener never acks).
-- Only the listener's ack, via its own timestamped write, sets
-- processed_at - it's a separate write specifically so it never races the
-- transaction that recorded notified_at.

ALTER TABLE mock.shop_amazon_events
	ADD COLUMN notified_at TIMESTAMPTZ,
	ADD COLUMN processed_at TIMESTAMPTZ;

UPDATE mock.shop_amazon_events
	SET processed_at = NOW()
	WHERE processed;

ALTER TABLE mock.shop_amazon_events
	DROP COLUMN processed,
	DROP COLUMN processed_successfully;

DROP INDEX IF EXISTS mock.shop_amazon_events_by_timestamp_unprocessed;
CREATE INDEX shop_amazon_events_by_timestamp_unprocessed ON mock.shop_amazon_events (shop_id, event_timestamp) WHERE processed_at IS NULL;

COMMIT;