[chore] media and emoji refactoring (#3000)

* start updating media manager interface ready for storing attachments / emoji right away

* store emoji and media as uncached immediately, then (re-)cache on Processing{}.Load()

* remove now unused media workers

* fix tests and issues

* fix another test!

* fix emoji activitypub uri setting behaviour, fix remainder of test compilation issues

* fix more tests

* fix (most of) remaining tests, add debouncing to repeatedly failing media / emojis

* whoops, rebase issue

* remove kim's whacky experiments

* do some reshuffling, ensure emoji uri gets set

* ensure marked as not cached on cleanup

* tweaks to media / emoji processing to handle context canceled better

* ensure newly fetched emojis actually get set in returned slice

* use different varnames to be a bit more obvious

* move emoji refresh rate limiting to dereferencer

* add exported dereferencer functions for remote media, use these for recaching in processor

* add check for nil attachment in updateAttachment()

* remove unused emoji and media fields + columns

* see previous commit

* fix old migrations expecting image_updated_at to exists (from copies of old models)

* remove freshness checking code (seems to be broken...)

* fix error arg causing nil ptr exception

* finish documentating functions with comments, slight tweaks to media / emoji deref error logic

* remove some extra unneeded boolean checking

* finish writing documentation (code comments) for exported media manager methods

* undo changes to migration snapshot gtsmodels, updated failing migration to have its own snapshot

* move doesColumnExist() to util.go in migrations package

1 files changed, 40 insertions, 0 deletions

diff --git a/internal/db/bundb/migrations/util.go b/internal/db/bundb/migrations/util.go
new file mode 100644
index 000000000..47de09e23
--- /dev/null
+++ b/internal/db/bundb/migrations/util.go
@@ -0,0 +1,40 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package migrations
+
+import (
+	"context"
+
+	"github.com/uptrace/bun"
+	"github.com/uptrace/bun/dialect"
+)
+
+// doesColumnExist safely checks whether given column exists on table, handling both SQLite and PostgreSQL appropriately.
+func doesColumnExist(ctx context.Context, tx bun.Tx, table, col string) (bool, error) {
+	var n int
+	var err error
+	switch tx.Dialect().Name() {
+	case dialect.SQLite:
+		err = tx.NewRaw("SELECT COUNT(*) FROM pragma_table_info(?) WHERE name=?", table, col).Scan(ctx, &n)
+	case dialect.PG:
+		err = tx.NewRaw("SELECT COUNT(*) FROM information_schema.columns WHERE table_name=? and column_name=?", table, col).Scan(ctx, &n)
+	default:
+		panic("unexpected dialect")
+	}
+	return (n > 0), err
+}