scrobblerlog: Allow configuring fallback time zone

Fixes #6

pkg/scrobblerlog/parser.go

@@ -71,10 +71,12 @@ type Record struct {
 
 // Represents a scrobbler log file.
 type ScrobblerLog struct {
-	TZ       TZInfo
-	Client   string
-	Records  []Record
-	location *time.Location
+	TZ      TZInfo
+	Client  string
+	Records []Record
+	// Timezone to be used for timestamps in the log file,
+	// if TZ is set to [TZ_UNKNOWN].
+	FallbackTimezone *time.Location
 }
 
 func (l *ScrobblerLog) Parse(data io.Reader, includeSkipped bool) error {
@@ -173,7 +175,6 @@ func (l *ScrobblerLog) ReadHeader(reader *bufio.Reader) error {
 			timezone, found := strings.CutPrefix(text, "#TZ/")
 			if found {
 				l.TZ = TZInfo(timezone)
-				l.location = locationFromTimezone(l.TZ)
 				continue
 			}
 
@@ -223,6 +224,11 @@ func (l ScrobblerLog) rowToRecord(row []string) (Record, error) {
 		return record, err
 	}
 
+	var timezone *time.Location = nil
+	if l.TZ == TZ_UNKNOWN {
+		timezone = l.FallbackTimezone
+	}
+
 	record = Record{
 		ArtistName:  row[0],
 		AlbumName:   row[1],
@@ -230,7 +236,7 @@ func (l ScrobblerLog) rowToRecord(row []string) (Record, error) {
 		TrackNumber: trackNumber,
 		Duration:    time.Duration(duration) * time.Second,
 		Rating:      Rating(row[5]),
-		Timestamp:   timeFromLocalTimestamp(timestamp, l.location),
+		Timestamp:   timeFromLocalTimestamp(timestamp, timezone),
 	}
 
 	if len(row) > 7 {
@@ -240,26 +246,20 @@ func (l ScrobblerLog) rowToRecord(row []string) (Record, error) {
 	return record, nil
 }
 
-// Convert the timezone string from the header to a time.Location.
-// Often this is set to "UNKNOWN" in the log file, in which case it defaults
-// to UTC.
-func locationFromTimezone(timezone TZInfo) *time.Location {
-	location, err := time.LoadLocation(string(timezone))
-	if err != nil {
-		return time.UTC
-	}
-	return location
-}
-
-// Convert a Unix timestamp to a time.Time object, but treat the timestamp
+// Convert a Unix timestamp to a [time.Time] object, but treat the timestamp
 // as being in the given location's timezone instead of UTC.
+// If location is nil, the timestamp is returned as UTC.
 func timeFromLocalTimestamp(timestamp int64, location *time.Location) time.Time {
 	t := time.Unix(timestamp, 0)
 
-	// The time is now in UTC. Get the offset to the requested timezone.
-	_, offset := t.In(location).Zone()
-	if offset != 0 {
-		t = t.Add(time.Duration(offset) * time.Second)
+	// The time is now in UTC. Get the offset to the requested timezone
+	// and shift the time accordingly.
+	if location != nil {
+		_, offset := t.In(location).Zone()
+		if offset != 0 {
+			t = t.Add(time.Duration(offset) * time.Second)
+		}
 	}
+
 	return t
 }

pkg/scrobblerlog/parser_test.go

@@ -81,6 +81,21 @@ func TestParserExcludeSkipped(t *testing.T) {
 		record4.MusicBrainzRecordingID)
 }
 
+func TestParserFallbackTimezone(t *testing.T) {
+	assert := assert.New(t)
+	data := bytes.NewBufferString(testScrobblerLog)
+	result := scrobblerlog.ScrobblerLog{
+		FallbackTimezone: time.FixedZone("UTC+2", 7200),
+	}
+	err := result.Parse(data, false)
+	require.NoError(t, err)
+	record1 := result.Records[0]
+	assert.Equal(
+		time.Unix(1260342084, 0).Add(2*time.Hour),
+		record1.Timestamp,
+	)
+}
+
 func TestAppend(t *testing.T) {
 	assert := assert.New(t)
 	data := make([]byte, 0, 10)