Add Iceshrimp migration docs

content/en/docs/install/migrate.md

@@ -266,3 +266,174 @@ If you use an object store such as S3, double-check your settings
 be able to search notes, you must enable it via the "roles" system.
 
 Congratulations, you're now running Sharkey!
+
+## From Iceshrimp
+
+This guide was only tested on an Iceshrimp-JS instance, on version v20223.12.11. Iceshrimp.NET is not supported,
+and as far as known, the migration from Iceshrimp-JS to Iceshrimp.NET is a one way street.
+Furthermore, this was tested on a **vanilla** Iceshrimp-JS instance. Other Iceshrimp instances
+that may run with custom patches may require a different treatment.
+
+If any of the steps fails, especially SQL queries, seek help from us
+[Via Discord](https://discord.gg/8hF6pMVWja). Do *not* try fixing things
+in the DB yourself unless you *really* know what you are doing.
+
+Before you begin, please take a backup of your database. While you're
+there, make sure you know how to restore from that backup! Using the
+`plain` format for `pg_dump` is probably the simplest way.
+
+It's a good idea to have a separate backup of your list of silenced
+instances and of your `user` table.
+
+### Using Docker
+
+Stop / shut down the entire stack: PostgreSQL, Redis / Valkey and
+Iceshrimp itself. Stop all of it.
+
+Now is the time to *backup* your database and Redis volumes!
+
+You will need to revert Iceshrimp migrations back to the last common one with
+Firefish, which should leave you on Firefish 1.0.2 schema.
+
+First, connect to the database container. Start *only* the database with `docker compose up -d db`
+(instead of `db`, you may need to use whatever name is set for the service in
+your docker compose config), and start a `psql` shell with `docker
+exec -it db psql -U iceshrimp -d iceshrimp` (replace `db` as before, and
+`-U iceshrimp -d iceshrimp` with the database user and database name,
+respectively, if they're different from `iceshrimp`).
+
+You should now be connected to your Iceshrimp database. We need first to delete from the
+tables 3 of the Iceshrimp migrations that are not able to be reverted, regarding OAuth and
+instance's max character limit. Don't worry, the OAuth is going to be dropped enterily by
+one of the migration reverts, and the max character limit does not conflict with Sharkey, and
+in fact, could be overwritten safely by a Sharkey migration.
+
+Make sure you have a backup safely stored, and then delete the mentioned
+migrations with the following queries:
+```sql
+DELETE FROM "migrations" WHERE "name" = 'IncreaseHostCharLimit1701118152149';
+DELETE FROM "migrations" WHERE "name" = 'IncreaseOauthTokenRedirecturisLength1697286869039';
+DELETE FROM "migrations" WHERE "name" = 'IncreaseOAuthRedirecturisLength1697246035867';
+```
+
+We are now ready to start reverting Iceshrimp migrations.
+Edit the `docker-compose.yml` file and add `entrypoint: /bin/sh` to the web section of the file.
+Save the file and start the container with `docker-compose up -d web`, and then run
+`docker exec -it iceshrimp_web sh`.
+Replace "iceshrimp_web" with the name of your container if you've changed it.
+
+Now, navigate to the Iceshrimp directory, and inside of it, nagivate to `packages/backend`.
+The command to run in order to revert the latest applies migration is
+```
+yarn run typeorm migration:revert -d built/ormconfig.js
+```
+You'll have to run it several times, until you see that `IceshrimpRepo1689965609061` has been reverted.
+You're now back on the Firefish 1.0.2 database scheme.
+Exit the shell and run `docker compose down web` to stop the Iceshrimp container.
+
+Now, edit you docker compose and replace the Iceshrimp image with
+`registry.activitypub.software/transfem-org/sharkey:latest`
+
+Backup your Iceshrimp config and replace it with the [default
+Sharkey one](https://activitypub.software/TransFem-org/Sharkey/-/raw/stable/.config/docker_example.yml)
+
+Edit the config inline with your instance settings. Make sure to use
+the same `db` & `redis` settings as in your Iceshrimp config.
+
+Make sure to update the *mount paths* for volumes of the Sharkey
+container from `/iceshrimp/` to `/sharkey/` (so your existing volumes
+will show up at the new path, inside the container).
+
+Now we need to massage the database into shape so that Sharkey database migrations will
+work. The following series of SQL queries / commands should do it, but
+please read the comments and pay attention to the results after each
+query!
+
+```sql
+-- start a transaction, so we won't leave the db in a halfway state if
+-- things go wrong
+BEGIN;
+
+-- move aside some existing columns; Sharkey migrations will
+-- re-create them; we don't `DROP` them because we want to keep the data
+ALTER TABLE "user" RENAME COLUMN "movedToUri" TO "ish_movedToUri";
+ALTER TABLE "user" RENAME COLUMN "alsoKnownAs" TO "ish_alsoKnownAs";
+ALTER TABLE "user" RENAME COLUMN "speakAsCat" TO "ish_speakAsCat";
+ALTER TABLE "user_profile" RENAME COLUMN "preventAiLearning" TO "ish_preventAiLearning";
+ALTER TABLE "meta" RENAME COLUMN "silencedHosts" TO "ish_silencedHosts";
+
+-- this column was added by both Iceshrimp, and Misskey, but with
+-- different names, let's fix it
+ALTER TABLE "meta" RENAME COLUMN "ToSUrl" TO "termsOfServiceUrl";
+
+-- update antenna types, this is only needed on some instances but
+-- recommend to run anyway
+--
+-- this *removes* any antennas of types not supported by Sharkey!
+CREATE TYPE public.new_antenna_src_enum AS ENUM ('home', 'all', 'list');
+ALTER TABLE antenna ADD COLUMN new_src public.new_antenna_src_enum;
+DELETE FROM antenna WHERE src NOT IN ('home', 'all', 'list');
+ALTER TABLE antenna DROP COLUMN src;
+ALTER TABLE antenna RENAME COLUMN new_src TO src;
+DROP TYPE public.antenna_src_enum;
+ALTER TYPE new_antenna_src_enum RENAME TO antenna_src_enum;
+
+-- optional but recommended: delete all empty moderation log entries
+DELETE FROM moderation_log WHERE info = '{}';
+
+-- only needed on some instances, run this if
+-- `\dT+ user_profile_mutingnotificationtypes_enum`
+-- does not show `note` in the "elements" section
+ALTER TYPE "public"."user_profile_mutingnotificationtypes_enum" ADD VALUE 'note';
+```
+
+If everything worked and you saw no errors, you can run `COMMIT;` in
+that same `psql` shell, to commit all the changes, then close that
+shell. Again, if anything went wrong, come talk to us on
+[Matrix](https://matrix.to/#/#sharkey-support:shourai.de) or
+[Discord](https://discord.gg/8hF6pMVWja)!
+
+Start Sharkey, and let it run all its migrations. Once that's done,
+and Starkey says it's listening, stop Sharkey but keep the database
+running.
+
+Open another `psql` shell like before (`docker exec -it db psql -U
+firefish -d firefish`, replacing things as before). We need another
+small pass of massaging.
+
+```sql
+BEGIN;
+
+-- all existing users are approved, because Firefish doesn't have a
+-- concept of approvals
+UPDATE "user" SET approved = true;
+
+-- now we put back the data we moved aside
+UPDATE "user" SET "movedToUri" = "ish_movedToUri" WHERE "ish_movedToUri" IS NOT NULL;
+UPDATE "user" SET "alsoKnownAs" = "ish_alsoKnownAs" WHERE "ish_alsoKnownAs" IS NOT NULL;
+UPDATE "user" SET "speakAsCat" = COALESCE("ish_speakAsCat", false);
+UPDATE "user_profile" SET "preventAiLearning" = COALESCE("ish_preventAiLearning", true);
+UPDATE "meta" SET "silencedHosts" = COALESCE("ish_silencedHosts",'{}');
+
+ALTER TABLE "user" DROP COLUMN "ish_movedToUri";
+ALTER TABLE "user" DROP COLUMN "ish_alsoKnownAs";
+ALTER TABLE "user" DROP COLUMN "ish_speakAsCat";
+ALTER TABLE "user_profile" DROP COLUMN "ish_preventAiLearning";
+ALTER TABLE "meta" DROP COLUMN "ish_silencedHosts";
+
+```
+
+If everything worked and you saw no errors, you can run `COMMIT;` in
+that same `psql` shell, to commit all the changes, then close that
+shell. Again, if anything went wrong, come talk to us on
+[Discord](https://discord.gg/8hF6pMVWja)!
+
+Start everything up again, you should see no errors in the logs.
+
+Log in as an administrator, and go to the control panel.
+If you use an object store such as S3, double-check your settings
+(it's possible, for example, that the URL now looks like
+`https://https://yourdomain.com`, fix it). If you want your users to
+be able to search notes, you must enable it via the "roles" system.
+
+Congratulations, you're now running Sharkey!