-- Nachklang e.V. Calendar module — step 4 of docs/calendar-auth-migration.md,
-- the cutover. Apply manually against the CALENDAR_DB database, after 002,
-- and BEFORE deploying the API build that goes with it:
--   mysql -h <DB_HOST> -u <DB_USER> -p <CALENDAR_DB> < 003_allow_null_legacy_creator.sql
--
-- From the cutover on, an event's creator is an admin-module user id. There is
-- no legacy calendar user id to write any more, and `events.created_by_id` is
-- NOT NULL - so without this the very first event created after the deploy
-- fails to insert. `event_versions.version_created_by_id` is already nullable.
--
-- The foreign key to `users` is kept: it permits NULL, so it costs nothing
-- until step 5 drops the column and the table together.
--
-- Applying this early is harmless. Widening a column to accept NULL cannot
-- break the running pre-cutover build, which always supplies a value, so this
-- can go out ahead of the deploy rather than during it.

ALTER TABLE `events`
    MODIFY COLUMN `created_by_id` INT(11) NULL DEFAULT NULL;

-- Re-run of 002's backfill, to catch anything created between the two
-- migrations while the legacy path was still writing events. Idempotent by
-- construction: it only touches rows that have no snapshot yet.
UPDATE `events` e
    JOIN `users` u ON u.user_id = e.created_by_id
    SET e.created_by_name = u.full_name
    WHERE e.created_by_name IS NULL;

UPDATE `event_versions` v
    JOIN `users` u ON u.user_id = v.version_created_by_id
    SET v.version_created_by_name = u.full_name
    WHERE v.version_created_by_name IS NULL;