feat: add monitoring retention controls

go-backend/internal/store/repo/repository.go

@@ -65,7 +65,8 @@ type TunnelQuality = model.TunnelQuality
 // ─── Repository ──────────────────────────────────────────────────────
 
 type Repository struct {
-	db *gorm.DB
+	db     *gorm.DB
+	dbPath string
 }
 
 type FlowUploadCounterDelta struct {
@@ -198,7 +199,7 @@ func Open(path string) (*Repository, error) {
 		return nil, err
 	}
 
-	return &Repository{db: db}, nil
+	return &Repository{db: db, dbPath: path}, nil
 }
 
 func OpenPostgres(dsn string) (*Repository, error) {

go-backend/internal/store/repo/repository_storage.go

@@ -0,0 +1,72 @@
+package repo
+
+import (
+	"errors"
+	"fmt"
+	"os"
+)
+
+type DatabaseStorageSummary struct {
+	DBType            string `json:"dbType"`
+	DatabaseSizeBytes int64  `json:"databaseSizeBytes"`
+	DatabaseSizeText  string `json:"databaseSizeText"`
+}
+
+func (r *Repository) DatabaseStorageSummary() (DatabaseStorageSummary, error) {
+	if r == nil || r.db == nil {
+		return DatabaseStorageSummary{}, errors.New("repository not initialized")
+	}
+
+	switch r.db.Dialector.Name() {
+	case "sqlite":
+		size, err := sqliteDatabaseFileSize(r.dbPath)
+		if err != nil {
+			return DatabaseStorageSummary{}, err
+		}
+		return DatabaseStorageSummary{DBType: "sqlite", DatabaseSizeBytes: size, DatabaseSizeText: formatDatabaseSize(size)}, nil
+	case "postgres":
+		var size int64
+		if err := r.db.Raw("SELECT pg_database_size(current_database())").Scan(&size).Error; err != nil {
+			return DatabaseStorageSummary{}, err
+		}
+		return DatabaseStorageSummary{DBType: "postgres", DatabaseSizeBytes: size, DatabaseSizeText: formatDatabaseSize(size)}, nil
+	default:
+		return DatabaseStorageSummary{}, fmt.Errorf("unsupported database dialect %q", r.db.Dialector.Name())
+	}
+}
+
+func sqliteDatabaseFileSize(path string) (int64, error) {
+	if path == "" || path == ":memory:" {
+		return 0, nil
+	}
+
+	var total int64
+	for _, candidate := range []string{path, path + "-wal", path + "-shm"} {
+		info, err := os.Stat(candidate)
+		if err != nil {
+			if os.IsNotExist(err) {
+				continue
+			}
+			return 0, err
+		}
+		if !info.IsDir() {
+			total += info.Size()
+		}
+	}
+	return total, nil
+}
+
+func formatDatabaseSize(bytes int64) string {
+	if bytes < 1024 {
+		return fmt.Sprintf("%d B", bytes)
+	}
+	units := []string{"KB", "MB", "GB", "TB"}
+	value := float64(bytes) / 1024
+	for _, unit := range units {
+		if value < 1024 || unit == "TB" {
+			return fmt.Sprintf("%.1f %s", value, unit)
+		}
+		value /= 1024
+	}
+	return fmt.Sprintf("%d B", bytes)
+}

go-backend/internal/store/repo/repository_storage_test.go

@@ -0,0 +1,52 @@
+package repo
+
+import (
+	"path/filepath"
+	"testing"
+
+	"go-backend/internal/store/model"
+)
+
+func TestDatabaseStorageSummarySQLiteIncludesSize(t *testing.T) {
+	dbPath := filepath.Join(t.TempDir(), "storage.db")
+	r, err := Open(dbPath)
+	if err != nil {
+		t.Fatalf("open repo: %v", err)
+	}
+	defer r.Close()
+
+	if err := r.InsertNodeMetric(&model.NodeMetric{NodeID: 1, Timestamp: 123, CPUUsage: 1}); err != nil {
+		t.Fatalf("insert metric: %v", err)
+	}
+
+	summary, err := r.DatabaseStorageSummary()
+	if err != nil {
+		t.Fatalf("storage summary: %v", err)
+	}
+	if summary.DBType != "sqlite" {
+		t.Fatalf("expected sqlite db type, got %q", summary.DBType)
+	}
+	if summary.DatabaseSizeBytes <= 0 {
+		t.Fatalf("expected database size > 0, got %d", summary.DatabaseSizeBytes)
+	}
+	if summary.DatabaseSizeText == "" {
+		t.Fatalf("expected formatted size")
+	}
+}
+
+func TestFormatDatabaseSize(t *testing.T) {
+	tests := []struct {
+		bytes int64
+		want  string
+	}{
+		{bytes: 0, want: "0 B"},
+		{bytes: 512, want: "512 B"},
+		{bytes: 1024, want: "1.0 KB"},
+		{bytes: 1024 * 1024, want: "1.0 MB"},
+	}
+	for _, tc := range tests {
+		if got := formatDatabaseSize(tc.bytes); got != tc.want {
+			t.Fatalf("formatDatabaseSize(%d) = %q, want %q", tc.bytes, got, tc.want)
+		}
+	}
+}