-- Sync protocol 2.
--
-- Rows are now written only by compare-and-swap on change_seq (see
-- server/src/db.ts), keyed by a JSON array of the key's values, and every
-- user's data belongs to an epoch: a random id that changes whenever the
-- server's copy is thrown away, so a client can tell it is talking to a
-- server that no longer holds what it pushed and must hydrate from scratch.

CREATE TABLE IF NOT EXISTS sync_meta (
  k TEXT PRIMARY KEY,
  v TEXT NOT NULL
);

CREATE TABLE IF NOT EXISTS sync_epoch (
  user_id TEXT PRIMARY KEY,
  epoch   TEXT NOT NULL
);

-- Protocol 1 rows cannot be read as protocol 2: their keys were joined with
-- a space and every one was ordered by a client's clock. They are dropped
-- once, and each user's epoch with them — so every client re-hydrates and
-- offers its own database back, which is the copy that was always the
-- source of truth. No deployment held protocol 1 data when this shipped.
DO $$
BEGIN
  IF NOT EXISTS (SELECT 1 FROM sync_meta WHERE k = 'protocol' AND v = '2') THEN
    DELETE FROM sync_row;
    DELETE FROM sync_epoch;
    INSERT INTO sync_meta (k, v) VALUES ('protocol', '2')
      ON CONFLICT (k) DO UPDATE SET v = EXCLUDED.v;
  END IF;
END $$;