feat: make database migration testable and backfill assets

migration.go

@@ -0,0 +1,78 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"gorm.io/gorm"
+)
+
+// migrateDatabase applies schema changes and repairs legacy indexes. It is
+// intentionally separate from startup so migration behavior can be tested on
+// a disposable SQLite database before touching production data.
+func migrateDatabase(db *gorm.DB) error {
+	if err := db.AutoMigrate(&Task{}, &MediaAsset{}, &Setting{}, &User{}, &UserPermission{}, &CreditAccount{}, &CreditTransaction{}, &CreditReservation{}, &RedeemBatch{}, &RedeemCode{}, &RedeemRecord{}, &WebDAVConfig{}, &Session{}, &AuditLog{}); err != nil {
+		return err
+	}
+	if err := db.Exec("DROP INDEX IF EXISTS idx_tasks_source_rid_quality").Error; err != nil {
+		return err
+	}
+	if err := db.Exec("CREATE UNIQUE INDEX IF NOT EXISTS idx_tasks_user_source_rid_quality ON tasks(user_id, source, r_id, quality)").Error; err != nil {
+		return err
+	}
+	if err := db.Exec("DROP INDEX IF EXISTS idx_credit_reservations_task_id").Error; err != nil {
+		return err
+	}
+	return db.Exec("CREATE INDEX IF NOT EXISTS idx_credit_reservations_task_id ON credit_reservations(task_id)").Error
+}
+
+// backfillMediaAssets turns legacy completed tasks into shared media assets.
+// Existing physical files are reused; no media is moved or deleted.
+func backfillMediaAssets(db *gorm.DB, downloadDir string) error {
+	var tasks []Task
+	if err := db.Where("(asset_id = 0 OR asset_id IS NULL) AND status = ?", "done").Find(&tasks).Error; err != nil {
+		return err
+	}
+	for i := range tasks {
+		t := &tasks[i]
+		key := assetKey(t.Source, t.RID, t.Quality)
+		var asset MediaAsset
+		result := db.Where("asset_key = ?", key).Limit(1).Find(&asset)
+		if result.Error != nil {
+			return result.Error
+		}
+		if result.RowsAffected == 0 {
+			asset = MediaAsset{
+				AssetKey:      key,
+				Source:        t.Source,
+				RID:           t.RID,
+				Quality:       t.Quality,
+				LocalPath:     t.LocalPath,
+				Format:        t.Format,
+				ActualQuality: t.ActualQuality,
+				Size:          t.DownloadedBytes,
+				Status:        "done",
+			}
+			if asset.LocalPath != "" {
+				if fi, statErr := os.Stat(asset.LocalPath); statErr == nil && fi.Size() > 0 {
+					asset.Size = fi.Size()
+				}
+			} else if downloadDir != "" {
+				candidate := filepath.Join(downloadDir, safe(t.Artist)+" - "+safe(t.Title)+"."+t.Format)
+				if fi, statErr := os.Stat(candidate); statErr == nil && fi.Size() > 0 {
+					asset.LocalPath, asset.Size = candidate, fi.Size()
+				}
+			}
+			if err := db.Create(&asset).Error; err != nil {
+				return fmt.Errorf("create media asset for task %d: %w", t.ID, err)
+			}
+		}
+		if t.AssetID != asset.ID {
+			if err := db.Model(t).Update("asset_id", asset.ID).Error; err != nil {
+				return fmt.Errorf("link media asset for task %d: %w", t.ID, err)
+			}
+		}
+	}
+	return nil
+}