-- 0101_library_changes_keep_latest.up.sql — the change feed keeps every
-- entity's latest change, so an app syncing from nothing gets the whole
-- library.
--
-- Until now the compactor dropped every row older than 30 days. An app
-- syncing from cursor 0 (a fresh install, cleared data, or a reset after a
-- 410) builds its library from the feed, so it got only what had changed in
-- the last 30 days. From here the compactor drops a row only once a newer row
-- for the same entity exists, and drops a delete only once it is 30 days old.
--
--   idx_library_changes_entity   finds an entity's rows, newest first, for
--                                the compactor and the fill below.
--   library_changes_trimmed      one row: the highest id of a delete the
--                                compactor has dropped. An app whose cursor
--                                is below it may have missed that delete, so
--                                it is told to start over (410). It starts
--                                where the old compactor left off: everything
--                                below the oldest remaining row is gone.
--
-- Then every artist, album and track whose latest row is not an upsert, or
-- which has no row at all (the old compactor dropped it), gets one, artists
-- first so an album never arrives before its artist. Likes and playlists are
-- left as they are: the apps fetch those from their own endpoints.
CREATE INDEX idx_library_changes_entity ON library_changes (entity_type, entity_id, id DESC);

CREATE TABLE library_changes_trimmed (
    id      boolean PRIMARY KEY DEFAULT true CONSTRAINT library_changes_trimmed_one_row CHECK (id),
    through bigint NOT NULL DEFAULT 0
);

INSERT INTO library_changes_trimmed (through)
SELECT COALESCE(min(id), 1) - 1 FROM library_changes;

INSERT INTO library_changes (entity_type, entity_id, op)
SELECT 'artist', a.id::text, 'upsert'
  FROM artists a
 WHERE COALESCE((SELECT c.op FROM library_changes c
                  WHERE c.entity_type = 'artist' AND c.entity_id = a.id::text
                  ORDER BY c.id DESC LIMIT 1), 'delete') <> 'upsert'
 ORDER BY a.id;

INSERT INTO library_changes (entity_type, entity_id, op)
SELECT 'album', al.id::text, 'upsert'
  FROM albums al
 WHERE COALESCE((SELECT c.op FROM library_changes c
                  WHERE c.entity_type = 'album' AND c.entity_id = al.id::text
                  ORDER BY c.id DESC LIMIT 1), 'delete') <> 'upsert'
 ORDER BY al.id;

INSERT INTO library_changes (entity_type, entity_id, op)
SELECT 'track', t.id::text, 'upsert'
  FROM tracks t
 WHERE COALESCE((SELECT c.op FROM library_changes c
                  WHERE c.entity_type = 'track' AND c.entity_id = t.id::text
                  ORDER BY c.id DESC LIMIT 1), 'delete') <> 'upsert'
 ORDER BY t.id;