-- =====================================================
-- Optimistic Locking for Courses, Events, Bookings
--
-- Problem: Concurrent edits to courses, events, or bookings
-- can silently overwrite each other (last write wins).
--
-- Fix: Add version column to each table with an auto-
-- increment trigger on update. API layer checks version
-- match before writing, preventing silent overwrites.
--
-- Reuses the same trigger function pattern established
-- in 20260416000005_member_versioning.sql but creates a
-- shared generic function instead of table-specific ones.
-- =====================================================

-- Shared version increment function (CREATE OR REPLACE is idempotent)
CREATE OR REPLACE FUNCTION public.increment_version()
RETURNS trigger
LANGUAGE plpgsql AS $$
BEGIN
  NEW.version := OLD.version + 1;
  RETURN NEW;
END;
$$;

-- -------------------------------------------------------
-- COURSES
-- -------------------------------------------------------

ALTER TABLE public.courses
  ADD COLUMN IF NOT EXISTS version integer NOT NULL DEFAULT 1;

DO $$
BEGIN
  IF NOT EXISTS (
    SELECT 1 FROM pg_trigger WHERE tgname = 'trg_courses_increment_version'
  ) THEN
    CREATE TRIGGER trg_courses_increment_version
      BEFORE UPDATE ON public.courses
      FOR EACH ROW
      EXECUTE FUNCTION public.increment_version();
  END IF;
END;
$$;

-- -------------------------------------------------------
-- EVENTS
-- -------------------------------------------------------

ALTER TABLE public.events
  ADD COLUMN IF NOT EXISTS version integer NOT NULL DEFAULT 1;

DO $$
BEGIN
  IF NOT EXISTS (
    SELECT 1 FROM pg_trigger WHERE tgname = 'trg_events_increment_version'
  ) THEN
    CREATE TRIGGER trg_events_increment_version
      BEFORE UPDATE ON public.events
      FOR EACH ROW
      EXECUTE FUNCTION public.increment_version();
  END IF;
END;
$$;

-- -------------------------------------------------------
-- BOOKINGS
-- -------------------------------------------------------

ALTER TABLE public.bookings
  ADD COLUMN IF NOT EXISTS version integer NOT NULL DEFAULT 1;

DO $$
BEGIN
  IF NOT EXISTS (
    SELECT 1 FROM pg_trigger WHERE tgname = 'trg_bookings_increment_version'
  ) THEN
    CREATE TRIGGER trg_bookings_increment_version
      BEFORE UPDATE ON public.bookings
      FOR EACH ROW
      EXECUTE FUNCTION public.increment_version();
  END IF;
END;
$$;