-- =============================================================================
-- Vignette · migration 21 — learner-persona별 단일 활성 회기
-- =============================================================================
-- 기존 DB 적용 전 owner가 아래 읽기 전용 점검을 실행한다.
-- 중복 또는 실패 후 남은 invalid index가 있으면 임의 종료·DROP 하지 말고
-- 소유자가 보존·복구 방식을 결정해야 한다.
--
-- SELECT learner_id, persona_id, count(*)
-- FROM app.sessions
-- WHERE ended_at IS NULL AND persona_id IS NOT NULL
-- GROUP BY learner_id, persona_id
-- HAVING count(*) > 1;
--
-- CREATE INDEX CONCURRENTLY는 transaction block 안에서 실행할 수 없다.
-- release agent가 online migration으로 owner psql에 전달한다.
-- 이 파일의 전·후 condition은 IF NOT EXISTS가 invalid/wrong index를 조용히
-- 건너뛰는 경우를 fail-closed로 막는다.

DO $$
DECLARE
  target_index oid := to_regclass('app.uq_sessions_one_active_learner_persona');
BEGIN
  IF EXISTS (
    SELECT 1
    FROM app.sessions
    WHERE ended_at IS NULL
      AND persona_id IS NOT NULL
    GROUP BY learner_id, persona_id
    HAVING count(*) > 1
  ) THEN
    RAISE EXCEPTION
      'migration 21 blocked: duplicate active learner-persona sessions exist';
  END IF;

  IF target_index IS NOT NULL AND NOT EXISTS (
    SELECT 1
    FROM pg_index AS index_meta
    WHERE index_meta.indexrelid = target_index
      AND index_meta.indrelid = 'app.sessions'::regclass
      AND index_meta.indisvalid
      AND index_meta.indisready
      AND index_meta.indisunique
      AND index_meta.indnkeyatts = 2
      AND pg_get_indexdef(index_meta.indexrelid, 1, true) = 'learner_id'
      AND pg_get_indexdef(index_meta.indexrelid, 2, true) = 'persona_id'
      AND regexp_replace(
        pg_get_expr(index_meta.indpred, index_meta.indrelid),
        '[[:space:]()]',
        '',
        'g'
      ) = 'ended_atISNULLANDpersona_idISNOTNULL'
  ) THEN
    RAISE EXCEPTION
      'migration 21 blocked: target index exists but is invalid or has a different definition';
  END IF;
END
$$;

CREATE UNIQUE INDEX CONCURRENTLY IF NOT EXISTS uq_sessions_one_active_learner_persona
  ON app.sessions (learner_id, persona_id)
  WHERE ended_at IS NULL AND persona_id IS NOT NULL;

DO $$
BEGIN
  IF NOT EXISTS (
    SELECT 1
    FROM pg_index AS index_meta
    WHERE index_meta.indexrelid = 'app.uq_sessions_one_active_learner_persona'::regclass
      AND index_meta.indrelid = 'app.sessions'::regclass
      AND index_meta.indisvalid
      AND index_meta.indisready
      AND index_meta.indisunique
      AND index_meta.indnkeyatts = 2
      AND pg_get_indexdef(index_meta.indexrelid, 1, true) = 'learner_id'
      AND pg_get_indexdef(index_meta.indexrelid, 2, true) = 'persona_id'
      AND regexp_replace(
        pg_get_expr(index_meta.indpred, index_meta.indrelid),
        '[[:space:]()]',
        '',
        'g'
      ) = 'ended_atISNULLANDpersona_idISNOTNULL'
  ) THEN
    RAISE EXCEPTION
      'migration 21 failed: valid target unique index was not created';
  END IF;
END
$$;