scotty/pkg/scrobblerlog/parser.go

/*
Copyright © 2023-2025 Philipp Wolfer <phw@uploadedlobster.com>

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
*/

// Package to parse and writer .scrobbler.log files as written by Rockbox.
//
// See
// - https://www.rockbox.org/wiki/LastFMLog
// - https://git.rockbox.org/cgit/rockbox.git/tree/apps/plugins/lastfm_scrobbler.c
package scrobblerlog

import (
	"bufio"
	"encoding/csv"
	"fmt"
	"io"
	"strconv"
	"strings"
	"time"

	"go.uploadedlobster.com/mbtypes"
)

// TZInfo is the timezone information in the header of the scrobbler log file.
// It can be "UTC" or "UNKNOWN", if the device writing the scrobbler log file
// knows the time, but not the timezone.
type TZInfo string

const (
	TZ_UNKNOWN TZInfo = "UNKNOWN"
	TZ_UTC     TZInfo = "UTC"
)

// L if listened at least 50% or S if skipped
type Rating string

const (
	RATING_LISTENED Rating = "L"
	RATING_SKIPPED  Rating = "S"
)

// A single entry of a track in the scrobbler log file.
type Record struct {
	ArtistName             string
	AlbumName              string
	TrackName              string
	TrackNumber            int
	Duration               time.Duration
	Rating                 Rating
	Timestamp              time.Time
	MusicBrainzRecordingID mbtypes.MBID
}

// Represents a scrobbler log file.
type ScrobblerLog struct {
	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, ignoreSkipped bool) error {
	l.Records = make([]Record, 0)

	reader := bufio.NewReader(data)
	err := l.ReadHeader(reader)
	if err != nil {
		return err
	}

	tsvReader := csv.NewReader(reader)
	tsvReader.Comma = '\t'
	// Row length is often flexible
	tsvReader.FieldsPerRecord = -1

	for {
		// A row is:
		// artistName	releaseName	trackName	trackNumber	duration	rating	timestamp	recordingMBID
		row, err := tsvReader.Read()
		if err == io.EOF {
			break
		} else if err != nil {
			return err
		}

		// fmt.Printf("row: %v\n", row)

		// We consider only the last field (recording MBID) optional
		if len(row) < 7 {
			line, _ := tsvReader.FieldPos(0)
			return fmt.Errorf("invalid record in scrobblerlog line %v", line)
		}

		record, err := l.rowToRecord(row)
		if err != nil {
			return err
		}

		if ignoreSkipped && record.Rating == RATING_SKIPPED {
			continue
		}

		l.Records = append(l.Records, record)
	}

	return nil
}

func (l *ScrobblerLog) Append(data io.Writer, records []Record) (lastTimestamp time.Time, err error) {
	tsvWriter := csv.NewWriter(data)
	tsvWriter.Comma = '\t'

	for _, record := range records {
		if record.Timestamp.After(lastTimestamp) {
			lastTimestamp = record.Timestamp
		}

		// A row is:
		// artistName	releaseName	trackName	trackNumber	duration	rating	timestamp	recordingMBID
		err = tsvWriter.Write([]string{
			record.ArtistName,
			record.AlbumName,
			record.TrackName,
			strconv.Itoa(record.TrackNumber),
			strconv.Itoa(int(record.Duration.Seconds())),
			string(record.Rating),
			strconv.FormatInt(record.Timestamp.Unix(), 10),
			string(record.MusicBrainzRecordingID),
		})
	}

	tsvWriter.Flush()
	return
}

func (l *ScrobblerLog) ReadHeader(reader *bufio.Reader) error {
	// Skip header
	for i := 0; i < 3; i++ {
		line, _, err := reader.ReadLine()
		if err != nil {
			return err
		}

		if len(line) == 0 || line[0] != '#' {
			err = fmt.Errorf("unexpected header (line %v)", i)
		} else {
			text := string(line)
			if i == 0 && !strings.HasPrefix(text, "#AUDIOSCROBBLER/1") {
				err = fmt.Errorf("not a scrobbler log file")
			}

			// The timezone can be set to "UTC" or "UNKNOWN", if the device writing
			// the log knows the time, but not the timezone.
			timezone, found := strings.CutPrefix(text, "#TZ/")
			if found {
				l.TZ = TZInfo(timezone)
				continue
			}

			client, found := strings.CutPrefix(text, "#CLIENT/")
			if found {
				l.Client = client
				continue
			}
		}

		if err != nil {
			return err
		}
	}
	return nil
}

func (l *ScrobblerLog) WriteHeader(writer io.Writer) error {
	headers := []string{
		"#AUDIOSCROBBLER/1.1\n",
		"#TZ/" + string(l.TZ) + "\n",
		"#CLIENT/" + l.Client + "\n",
	}
	for _, line := range headers {
		_, err := writer.Write([]byte(line))
		if err != nil {
			return err
		}
	}
	return nil
}

func (l ScrobblerLog) rowToRecord(row []string) (Record, error) {
	var record Record
	trackNumber, err := strconv.Atoi(row[3])
	if err != nil {
		return record, err
	}

	duration, err := strconv.Atoi(row[4])
	if err != nil {
		return record, err
	}

	timestamp, err := strconv.ParseInt(row[6], 10, 64)
	if err != nil {
		return record, err
	}

	var timezone *time.Location = nil
	if l.TZ == TZ_UNKNOWN {
		timezone = l.FallbackTimezone
	}

	record = Record{
		ArtistName:  row[0],
		AlbumName:   row[1],
		TrackName:   row[2],
		TrackNumber: trackNumber,
		Duration:    time.Duration(duration) * time.Second,
		Rating:      Rating(row[5]),
		Timestamp:   timeFromLocalTimestamp(timestamp, timezone),
	}

	if len(row) > 7 {
		record.MusicBrainzRecordingID = mbtypes.MBID(row[7])
	}

	return record, nil
}

// 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
	// 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
}