Move migrations into services and base into modules/migration (#17663)

* Move migrtions into services and base into modules/migration

* Fix imports

* Fix lint

services/migrations/update.go

@@ -0,0 +1,76 @@
+// Copyright 2019 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package migrations
+
+import (
+	"context"
+
+	"code.gitea.io/gitea/models"
+	"code.gitea.io/gitea/models/db"
+	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/modules/structs"
+)
+
+// UpdateMigrationPosterID updates all migrated repositories' issues and comments posterID
+func UpdateMigrationPosterID(ctx context.Context) error {
+	for _, gitService := range structs.SupportedFullGitService {
+		select {
+		case <-ctx.Done():
+			log.Warn("UpdateMigrationPosterID aborted before %s", gitService.Name())
+			return db.ErrCancelledf("during UpdateMigrationPosterID before %s", gitService.Name())
+		default:
+		}
+		if err := updateMigrationPosterIDByGitService(ctx, gitService); err != nil {
+			log.Error("updateMigrationPosterIDByGitService failed: %v", err)
+		}
+	}
+	return nil
+}
+
+func updateMigrationPosterIDByGitService(ctx context.Context, tp structs.GitServiceType) error {
+	provider := tp.Name()
+	if len(provider) == 0 {
+		return nil
+	}
+
+	const batchSize = 100
+	var start int
+	for {
+		select {
+		case <-ctx.Done():
+			log.Warn("UpdateMigrationPosterIDByGitService(%s) cancelled", tp.Name())
+			return nil
+		default:
+		}
+
+		users, err := models.FindExternalUsersByProvider(models.FindExternalUserOptions{
+			Provider: provider,
+			Start:    start,
+			Limit:    batchSize,
+		})
+		if err != nil {
+			return err
+		}
+
+		for _, user := range users {
+			select {
+			case <-ctx.Done():
+				log.Warn("UpdateMigrationPosterIDByGitService(%s) cancelled", tp.Name())
+				return nil
+			default:
+			}
+			externalUserID := user.ExternalID
+			if err := models.UpdateMigrationsByType(tp, externalUserID, user.UserID); err != nil {
+				log.Error("UpdateMigrationsByType type %s external user id %v to local user id %v failed: %v", tp.Name(), user.ExternalID, user.UserID, err)
+			}
+		}
+
+		if len(users) < batchSize {
+			break
+		}
+		start += len(users)
+	}
+	return nil
+}