Music player in the sound settings: pick any calm track or automatic

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/audio.rs

@@ -30,6 +30,36 @@ pub fn tracks_in(c: Category) -> Vec<usize> {
     TRACKS.iter().enumerate().filter(|(_, t)| t.1 == c).map(|(i, _)| i).collect()
 }
 
+// the calm tracks the music player offers (no battle, victory or defeat music)
+pub fn player_tracks() -> Vec<usize> {
+    use Category as C;
+    TRACKS.iter().enumerate().filter(|(_, t)| matches!(t.1, C::Title | C::Build | C::Surface | C::Torture | C::Temple)).map(|(i, _)| i).collect()
+}
+
+pub fn track_id(t: usize) -> &'static str {
+    TRACKS.get(t).map_or("", |t| t.0)
+}
+
+pub fn track_by_id(id: &str) -> Option<usize> {
+    if id.is_empty() {
+        return None;
+    }
+    TRACKS.iter().position(|t| t.0 == id)
+}
+
+// the song title stored in the XM module (without the "DungeonCraft - " prefix)
+pub fn track_title(t: usize) -> String {
+    let Some(d) = TRACKS.get(t).map(|t| t.2) else { return String::new() };
+    let raw = d.get(17..37).unwrap_or(&[]);
+    let name: String = raw.iter().take_while(|&&b| b != 0).map(|&b| b as char).collect();
+    let name = name.trim().trim_start_matches("DungeonCraft - ").trim().to_string();
+    if name.is_empty() {
+        track_id(t).to_string()
+    } else {
+        name
+    }
+}
+
 const MUSIC_GAIN: f32 = 0.45; // our replayer is ~4x louder than libopenmpt; leaves headroom for effects
 const SFX_GAIN: f32 = 0.55;
 
@@ -218,6 +248,20 @@ pub extern "C" fn dc_audio_render(frames: u32) -> *const f32 {
 mod tests {
     use super::*;
 
+    #[test]
+    fn the_music_player_offers_only_calm_tracks_with_titles() {
+        let l = player_tracks();
+        assert!(l.len() > 20);
+        for t in l {
+            let id = track_id(t);
+            assert!(!id.starts_with("battle") && !id.starts_with("victory") && id != "defeat" && !id.starts_with("assault"), "{}", id);
+            assert!(!track_title(t).is_empty());
+            assert_eq!(track_by_id(id), Some(t));
+        }
+        assert_eq!(track_by_id(""), None);
+        assert_eq!(track_title(track_by_id("build13").unwrap()), "Underground River");
+    }
+
     #[test]
     fn engine_crossfade_and_sfx() {
         dc_audio_init(48000.0);