[feature] Implement markers API (#1989)

* Implement markers API

Fixes #1856

* Correct import grouping in markers files

* Regenerate Swagger for markers API

* Shorten names for readability

* Cache markers for 6 hours

* Update DB ref

* Update envparsing.sh

internal/db/bundb/marker.go

@@ -0,0 +1,115 @@
+// 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 bundb
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"time"
+
+	"github.com/superseriousbusiness/gotosocial/internal/db"
+	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
+	"github.com/superseriousbusiness/gotosocial/internal/state"
+	"github.com/uptrace/bun"
+)
+
+type markerDB struct {
+	db    *WrappedDB
+	state *state.State
+}
+
+/*
+	MARKER FUNCTIONS
+*/
+
+func (m *markerDB) GetMarker(ctx context.Context, accountID string, name gtsmodel.MarkerName) (*gtsmodel.Marker, error) {
+	marker, err := m.state.Caches.GTS.Marker().Load(
+		"AccountID.Name",
+		func() (*gtsmodel.Marker, error) {
+			var marker gtsmodel.Marker
+
+			if err := m.db.NewSelect().
+				Model(&marker).
+				Where("? = ? AND ? = ?", bun.Ident("account_id"), accountID, bun.Ident("name"), name).
+				Scan(ctx); err != nil {
+				return nil, m.db.ProcessError(err)
+			}
+
+			return &marker, nil
+		},
+		accountID,
+		name,
+	)
+	if err != nil {
+		return nil, err // already processed
+	}
+
+	return marker, nil
+}
+
+func (m *markerDB) UpdateMarker(ctx context.Context, marker *gtsmodel.Marker) error {
+	prevMarker, err := m.GetMarker(ctx, marker.AccountID, marker.Name)
+	if err != nil && !errors.Is(err, db.ErrNoEntries) {
+		return fmt.Errorf("UpdateMarker: error fetching previous version of marker: %w", err)
+	}
+
+	marker.UpdatedAt = time.Now()
+	if prevMarker != nil {
+		marker.Version = prevMarker.Version + 1
+	}
+
+	return m.state.Caches.GTS.Marker().Store(marker, func() error {
+		if prevMarker == nil {
+			if _, err := m.db.NewInsert().
+				Model(marker).
+				Exec(ctx); err != nil {
+				return m.db.ProcessError(err)
+			}
+			return nil
+		}
+
+		// Optimistic concurrency control: start a transaction, try to update a row with a previously retrieved version.
+		// If the update in the transaction fails to actually change anything, another update happened concurrently, and
+		// this update should be retried by the caller, which in this case involves sending HTTP 409 to the API client.
+		return m.db.RunInTx(ctx, func(tx bun.Tx) error {
+			result, err := tx.NewUpdate().
+				Model(marker).
+				WherePK().
+				Where("? = ?", bun.Ident("version"), prevMarker.Version).
+				Exec(ctx)
+			if err != nil {
+				return m.db.ProcessError(err)
+			}
+
+			rowsAffected, err := result.RowsAffected()
+			if err != nil {
+				return m.db.ProcessError(err)
+			}
+			if rowsAffected == 0 {
+				// Will trigger a rollback, although there should be no changes to roll back.
+				return db.ErrAlreadyExists
+			} else if rowsAffected > 1 {
+				// This shouldn't happen.
+				return db.ErrNoEntries
+			}
+
+			return nil
+		})
+	})
+}