Make rescan asynchronous in background goroutine

TriggerRescan now returns immediately and runs the actual scan in a
30-minute timeout background goroutine. This prevents long scans from
tying up or timing out the HTTP request. Update related tests to wait
on a channel for the async scan to complete.

2 files changed, 22 insertions, 6 deletions

diff --git a/internal/service/admin.go b/internal/service/admin.go
index a775bed..673bf37 100644
--- a/internal/service/admin.go
+++ b/internal/service/admin.go
@@ -3,6 +3,7 @@ package service
 import (
 	"context"
 	"fmt"
+	"time"
 
 	"codeberg.org/snonux/player/internal/auth"
 	"codeberg.org/snonux/player/internal/clock"
@@ -39,10 +40,17 @@ func (s *adminService) TriggerRescan(ctx context.Context) error {
 	if s.scanner == nil {
 		return fmt.Errorf("scanner not configured")
 	}
-	// Use a background context so the scan isn't canceled when the HTTP request finishes.
-	if err := s.scanner.Scan(context.Background(), s.mediaRoot); err != nil {
-		return fmt.Errorf("scan failed: %w", err)
-	}
+	// Run the scan in a background goroutine so the HTTP request
+	// returns immediately and the scan continues asynchronously.
+	go func() {
+		ctx, cancel := context.WithTimeout(context.Background(), 30*time.Minute)
+		defer cancel()
+		if err := s.scanner.Scan(ctx, s.mediaRoot); err != nil {
+			fmt.Printf("[rescan] scan failed: %v\n", err)
+		} else {
+			fmt.Printf("[rescan] scan completed\n")
+		}
+	}()
 	return nil
 }
 
diff --git a/internal/service/admin_test.go b/internal/service/admin_test.go
index bef8ca2..ac73ce2 100644
--- a/internal/service/admin_test.go
+++ b/internal/service/admin_test.go
@@ -57,9 +57,11 @@ func TestAdminService_ListTrash(t *testing.T) {
 func TestAdminService_TriggerRescan(t *testing.T) {
 	ctx := context.Background()
 	var scannedRoot string
+	done := make(chan struct{})
 	sc := &fakeScanner{
 		scanFunc: func(_ context.Context, root string) error {
 			scannedRoot = root
+			close(done)
 			return nil
 		},
 	}
@@ -67,6 +69,8 @@ func TestAdminService_TriggerRescan(t *testing.T) {
 	if err := svc.TriggerRescan(ctx); err != nil {
 		t.Fatalf("unexpected error: %v", err)
 	}
+	<-done
+	// Give the background goroutine a moment to write scannedRoot.
 	if scannedRoot != "/media" {
 		t.Fatalf("expected root %q, got %q", "/media", scannedRoot)
 	}
@@ -74,16 +78,20 @@ func TestAdminService_TriggerRescan(t *testing.T) {
 
 func TestAdminService_TriggerRescan_Error(t *testing.T) {
 	ctx := context.Background()
+	done := make(chan struct{})
 	sc := &fakeScanner{
 		scanFunc: func(_ context.Context, _ string) error {
+			close(done)
 			return errors.New("scan failed")
 		},
 	}
 	svc := NewAdminService(&repository.MockStore{}, newMockClock(), &fakeHasher{fixed: "hash"}, sc, "/media")
 	err := svc.TriggerRescan(ctx)
-	if err == nil {
-		t.Fatal("expected error")
+	// TriggerRescan now always returns nil immediately; failure is logged in background.
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
 	}
+	<-done
 }
 
 func TestAdminService_TriggerRescan_NilScanner(t *testing.T) {