From 1543e155a871caed0a3f74c6c4d8c265c8890fd5 Mon Sep 17 00:00:00 2001
From: SAY-5 <say.apm35@gmail.com>
Date: Mon, 4 May 2026 19:22:34 -0700
Subject: [PATCH] fix(ui): guard against empty Files slice in buildDownloads

Skip ROMs whose cached row has has_multiple_files=false and an empty
Files slice (and log a warning) instead of indexing g.Files[0]. This
panic was reachable when an incremental cache update wrote a row
without a files array.

Fixes #223

Signed-off-by: SAY-5 <say.apm35@gmail.com>
---
 ui/download.go      |  8 ++++
 ui/download_test.go | 91 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 99 insertions(+)
 create mode 100644 ui/download_test.go

diff --git a/ui/download.go b/ui/download.go
index 230ab53..0f082e6 100644
--- a/ui/download.go
+++ b/ui/download.go
@@ -368,6 +368,14 @@ func (s *DownloadScreen) buildDownloads(config internal.Config, host romm.Host,
 			downloadLocation = filepath.Join(tmpDir, fmt.Sprintf("grout_multirom_%d.zip", g.ID))
 			sourceURL, _ = url.JoinPath(host.URL(), "/api/roms/", strconv.Itoa(g.ID), "content", g.FsName)
 		} else {
+			// Skip games with no file metadata to avoid an out-of-range panic.
+			// This can happen when the cached row was written without a
+			// `files` array (e.g. after an incremental cache update).
+			if len(g.Files) == 0 {
+				gaba.GetLogger().Warn("Skipping ROM with no file metadata; refresh the library to repopulate it",
+					"game", g.Name, "id", g.ID, "fs_name", g.FsName)
+				continue
+			}
 			// Find the file to download - use selected file if specified, otherwise first file
 			fileToDownload := g.Files[0]
 			if selectedFileID > 0 {
diff --git a/ui/download_test.go b/ui/download_test.go
new file mode 100644
index 0000000..b28600f
--- /dev/null
+++ b/ui/download_test.go
@@ -0,0 +1,91 @@
+package ui
+
+import (
+	"os"
+	"testing"
+
+	"grout/internal"
+	"grout/romm"
+)
+
+func TestMain(m *testing.M) {
+	// cfw.GetCFW() (called from buildDownloads) requires the CFW env var to
+	// be set to a recognised value, otherwise it terminates the process.
+	if os.Getenv("CFW") == "" {
+		os.Setenv("CFW", "ROCKNIX")
+	}
+	os.Exit(m.Run())
+}
+
+// TestBuildDownloads_EmptyFiles is a regression test for issue #223:
+// a cached ROM with HasMultipleFiles == false and an empty Files slice
+// must not panic. The entry should be skipped instead.
+func TestBuildDownloads_EmptyFiles(t *testing.T) {
+	s := NewDownloadScreen()
+	config := internal.Config{}
+	host := romm.Host{RootURI: "http://example.invalid"}
+	platform := romm.Platform{ID: 1, FSSlug: "nds", Name: "Nintendo DS"}
+
+	games := []romm.Rom{
+		{
+			ID:               60,
+			Name:             "Professor Layton and the Curious Village",
+			FsName:           "Professor Layton and the Curious Village (USA).nds",
+			FsNameNoExt:      "Professor Layton and the Curious Village (USA)",
+			HasMultipleFiles: false,
+			Files:            nil,
+		},
+	}
+
+	defer func() {
+		if r := recover(); r != nil {
+			t.Fatalf("buildDownloads panicked on empty Files slice: %v", r)
+		}
+	}()
+
+	downloads, artDownloads, gamelistEntries := s.buildDownloads(config, host, platform, games, 0)
+
+	if len(downloads) != 0 {
+		t.Errorf("expected 0 downloads when Files is empty, got %d", len(downloads))
+	}
+	if len(artDownloads) != 0 {
+		t.Errorf("expected 0 art downloads when Files is empty, got %d", len(artDownloads))
+	}
+	if len(gamelistEntries) != 0 {
+		t.Errorf("expected 0 gamelist entries when Files is empty, got %d", len(gamelistEntries))
+	}
+}
+
+// TestBuildDownloads_SingleFile_HappyPath sanity-checks that a normal
+// single-file ROM still produces a download URL after the empty-Files guard.
+func TestBuildDownloads_SingleFile_HappyPath(t *testing.T) {
+	s := NewDownloadScreen()
+	config := internal.Config{}
+	host := romm.Host{RootURI: "http://example.invalid"}
+	platform := romm.Platform{ID: 1, FSSlug: "nds", Name: "Nintendo DS"}
+
+	games := []romm.Rom{
+		{
+			ID:               42,
+			Name:             "Test Game",
+			FsName:           "test.nds",
+			FsNameNoExt:      "test",
+			HasMultipleFiles: false,
+			Files: []romm.RomFile{
+				{ID: 100, FileName: "test.nds"},
+			},
+		},
+	}
+
+	downloads, _, gamelistEntries := s.buildDownloads(config, host, platform, games, 0)
+
+	if len(downloads) != 1 {
+		t.Fatalf("expected 1 download, got %d", len(downloads))
+	}
+	if len(gamelistEntries) != 1 {
+		t.Fatalf("expected 1 gamelist entry, got %d", len(gamelistEntries))
+	}
+	if downloads[0].URL == "" {
+		t.Error("expected non-empty download URL")
+	}
+}