-- Nachklang e.V. Calendar module — step 5 preparation, brought forward.
-- Apply manually against the CALENDAR_DB database, after 001:
--   mysql -h <DB_HOST> -u <DB_USER> -p <CALENDAR_DB> < 002_snapshot_legacy_creator_names.sql
--
-- Snapshots the creator's and last editor's *name* onto the event itself.
--
-- Why: the creator is only ever rendered as a name (nothing authorises on it),
-- and today that name comes from joining the calendar's own `users` table.
-- Step 5 drops that table, which would silently erase the authorship of every
-- event created before the cutover. There is no account backfill to save them
-- either - that was dropped deliberately, see docs/calendar-auth-migration.md.
-- One text column per reference keeps the history at no ongoing cost.
--
-- These columns are an archive, not a source of truth. Nothing writes them
-- after this backfill: events created from the cutover onwards carry an admin
-- user id, whose name is resolved live so that renaming an account updates
-- everywhere. The read path prefers the live admin name, falls back to this
-- snapshot, and falls back again to the join until step 5 removes it.
--
-- The backfill is written to be idempotent (`WHERE ... IS NULL`) so it can be
-- re-run. Step 4's migration does exactly that, to catch anything created
-- between this migration and the cutover.
--
-- No charset clause: unlike 001's id columns these hold display text that is
-- only ever compared against other calendar data, so they inherit the tables'
-- utf8mb4_general_ci like the columns they are copied from.

ALTER TABLE `events`
    ADD COLUMN `created_by_name` VARCHAR(255) NULL DEFAULT NULL AFTER `created_by_user_id`;

ALTER TABLE `event_versions`
    ADD COLUMN `version_created_by_name` VARCHAR(255) NULL DEFAULT NULL AFTER `version_created_by_user_id`;

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;