improved library scan speeds, added library manager component

-libraries tab now opens a library manager
-choose library directory, manually soft scan and rescan
-batched db queues
-mp3 header-based duration extraction

backend/metadata/mp3duration_test.go

@@ -0,0 +1,117 @@
+package metadata
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+// testMP3Files returns the paths to all .mp3 files in the test_data
+// directory.  It skips the test if none are found.
+func testMP3Files(t *testing.T) []string {
+	t.Helper()
+
+	root := filepath.Join("..", "..", "test_data")
+
+	var files []string
+
+	err := filepath.Walk(root, func(
+		path string, info os.FileInfo, err error,
+	) error {
+		if err != nil {
+			return err
+		}
+
+		if !info.IsDir() && filepath.Ext(path) == ".mp3" {
+			files = append(files, path)
+		}
+
+		return nil
+	})
+	if err != nil {
+		t.Fatalf("walking test_data: %v", err)
+	}
+
+	if len(files) == 0 {
+		t.Skip("no .mp3 test fixtures found in test_data/")
+	}
+
+	return files
+}
+
+// TestGetMP3Duration_MatchesBeepDecode verifies that the fast
+// header-only parser produces a duration within 1 second of the
+// full decode via beep, for every test MP3 file.
+func TestGetMP3Duration_MatchesBeepDecode(t *testing.T) {
+	for _, path := range testMP3Files(t) {
+		t.Run(filepath.Base(path), func(t *testing.T) {
+			// Reference value: full beep decode.
+			refMS, err := GetTrackLengthMillis(path)
+			if err != nil {
+				t.Fatalf(
+					"beep decode failed: %v", err,
+				)
+			}
+
+			// Fast path.
+			f, err := os.Open(path)
+			if err != nil {
+				t.Fatalf("open: %v", err)
+			}
+
+			defer func() { _ = f.Close() }()
+
+			fastMS, err := getMP3Duration(f)
+			if err != nil {
+				t.Fatalf(
+					"getMP3Duration failed: %v", err,
+				)
+			}
+
+			diffMS := refMS - fastMS
+			if diffMS < 0 {
+				diffMS = -diffMS
+			}
+
+			// Allow up to 1 second of difference to account
+			// for rounding and the slight inaccuracy of the
+			// CBR fallback for VBR-without-Xing files.
+			const toleranceMS = 1000
+
+			t.Logf(
+				"beep=%dms  fast=%dms  diff=%dms",
+				refMS, fastMS, diffMS,
+			)
+
+			if diffMS > toleranceMS {
+				t.Errorf(
+					"duration mismatch: beep=%dms fast=%dms "+
+						"(diff %dms exceeds %dms tolerance)",
+					refMS, fastMS, diffMS, toleranceMS,
+				)
+			}
+		})
+	}
+}
+
+// TestGetMP3Duration_BasicParsing exercises the parser on a single
+// file and verifies a positive duration is returned.
+func TestGetMP3Duration_BasicParsing(t *testing.T) {
+	files := testMP3Files(t)
+
+	f, err := os.Open(files[0])
+	if err != nil {
+		t.Fatalf("open: %v", err)
+	}
+
+	defer func() { _ = f.Close() }()
+
+	ms, err := getMP3Duration(f)
+	if err != nil {
+		t.Fatalf("getMP3Duration: %v", err)
+	}
+
+	if ms <= 0 {
+		t.Errorf("expected positive duration, got %d", ms)
+	}
+}