nsm/crates/library/src/cue.rs

use std::fs;
use std::path::{Path, PathBuf};
use std::time::Duration;

#[derive(Debug, Clone)]
pub struct CueTrack {
    pub number: u32,
    pub title: String,
    pub performer: Option<String>,
    /// Начало трека (INDEX 01), абсолютное время от начала физического файла.
    pub start: Duration,
}

#[derive(Debug, Clone)]
pub struct CueSheet {
    pub album_title: Option<String>,
    pub album_performer: Option<String>,
    /// Абсолютный путь к аудиофайлу, на который ссылается cue (разрешён относительно
    /// расположения самого .cue файла).
    pub audio_path: PathBuf,
    pub tracks: Vec<CueTrack>,
}

/// Парсит .cue файл. Поддерживается только один `FILE` на лист (типичный случай —
/// весь альбом одним треком с cue-разметкой); мульти-файловые cue-листы — редкость,
/// для них будет использован только первый встреченный `FILE`.
pub fn parse_cue_file(cue_path: &Path) -> anyhow::Result<CueSheet> {
    let content = fs::read_to_string(cue_path)?;
    let dir = cue_path.parent().unwrap_or_else(|| Path::new("."));

    let mut album_title = None;
    let mut album_performer = None;
    let mut file_name: Option<String> = None;

    let mut tracks = Vec::new();
    let mut current_number: Option<u32> = None;
    let mut current_title: Option<String> = None;
    let mut current_performer: Option<String> = None;

    for raw in content.lines() {
        let line = raw.trim();
        if line.is_empty() {
            continue;
        }
        let upper = line.to_ascii_uppercase();

        if upper.starts_with("FILE ") {
            if file_name.is_none() {
                file_name = extract_quoted(line);
            }
        } else if let Some(rest) = upper.strip_prefix("TRACK ") {
            current_number = rest.split_whitespace().next().and_then(|s| s.parse().ok());
            current_title = None;
            current_performer = None;
        } else if upper.starts_with("TITLE ") {
            if current_number.is_some() {
                current_title = extract_quoted(line);
            } else {
                album_title = extract_quoted(line);
            }
        } else if upper.starts_with("PERFORMER ") {
            if current_number.is_some() {
                current_performer = extract_quoted(line);
            } else {
                album_performer = extract_quoted(line);
            }
        } else if let Some(rest) = upper.strip_prefix("INDEX 01 ") {
            if let (Some(num), Some(start)) = (current_number, parse_timecode(rest.trim())) {
                tracks.push(CueTrack {
                    number: num,
                    title: current_title
                        .clone()
                        .unwrap_or_else(|| format!("Track {num}")),
                    performer: current_performer.clone(),
                    start,
                });
            }
        }
        // INDEX 00 (пре-гэп), REM, CATALOG, FLAGS и т.п. — игнорируем, для базового
        // проигрывания не нужны.
    }

    let file_name =
        file_name.ok_or_else(|| anyhow::anyhow!("cue sheet has no FILE entry: {}", cue_path.display()))?;
    if tracks.is_empty() {
        anyhow::bail!("cue sheet has no tracks with INDEX 01: {}", cue_path.display());
    }

    Ok(CueSheet {
        album_title,
        album_performer,
        audio_path: dir.join(file_name),
        tracks,
    })
}

fn extract_quoted(line: &str) -> Option<String> {
    let start = line.find('"')?;
    let rest = &line[start + 1..];
    let end = rest.find('"')?;
    Some(rest[..end].to_string())
}

/// Формат таймкода cue — `MM:SS:FF`, где FF — кадры, 75 кадров в секунде (стандарт CD).
fn parse_timecode(s: &str) -> Option<Duration> {
    let parts: Vec<&str> = s.split(':').collect();
    if parts.len() != 3 {
        return None;
    }
    let mm: u64 = parts[0].parse().ok()?;
    let ss: u64 = parts[1].parse().ok()?;
    let ff: u64 = parts[2].parse().ok()?;
    Some(Duration::from_secs_f64(
        (mm * 60 + ss) as f64 + ff as f64 / 75.0,
    ))
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn parses_basic_cue_sheet() {
        let cue = r#"
PERFORMER "Test Artist"
TITLE "Test Album"
FILE "album.flac" WAVE
  TRACK 01 AUDIO
    TITLE "First Song"
    PERFORMER "Test Artist"
    INDEX 00 00:00:00
    INDEX 01 00:00:00
  TRACK 02 AUDIO
    TITLE "Second Song"
    INDEX 00 03:58:50
    INDEX 01 04:00:50
"#;
        let dir = tempfile::tempdir().unwrap();
        let cue_path = dir.path().join("album.cue");
        fs::write(&cue_path, cue).unwrap();

        let sheet = parse_cue_file(&cue_path).unwrap();
        assert_eq!(sheet.album_title.as_deref(), Some("Test Album"));
        assert_eq!(sheet.album_performer.as_deref(), Some("Test Artist"));
        assert_eq!(sheet.audio_path, dir.path().join("album.flac"));
        assert_eq!(sheet.tracks.len(), 2);
        assert_eq!(sheet.tracks[0].title, "First Song");
        assert_eq!(sheet.tracks[0].start, Duration::ZERO);
        assert_eq!(sheet.tracks[1].title, "Second Song");
        // 4:00 + 50/75 s
        let expected = Duration::from_secs_f64(4.0 * 60.0 + 50.0 / 75.0);
        assert!((sheet.tracks[1].start.as_secs_f64() - expected.as_secs_f64()).abs() < 0.001);
    }

    #[test]
    fn track_without_title_gets_fallback_name() {
        let cue = r#"
FILE "x.wav" WAVE
  TRACK 01 AUDIO
    INDEX 01 00:00:00
"#;
        let dir = tempfile::tempdir().unwrap();
        let cue_path = dir.path().join("x.cue");
        fs::write(&cue_path, cue).unwrap();

        let sheet = parse_cue_file(&cue_path).unwrap();
        assert_eq!(sheet.tracks[0].title, "Track 1");
    }
}