Add ChangePart command and buffered audio sink

Introduce a `ChangePart` variant to `AudioCmd` and a `current_part`
state in
`handle_audio`.  The audio sink is now created via
`DeviceSinkBuilder::from_default_device` with a fixed buffer size.
`load_audio`
now accepts a reference to `SoundrackParts`, and the player
automatically
queues the correct part when the queue becomes empty.

src/app/threads/audio.rs

@@ -1,4 +1,6 @@
-use rodio::{Decoder, DeviceSinkBuilder, MixerDeviceSink, Player, Source, source::Amplify};
+use rodio::{
+    Decoder, DeviceSinkBuilder, MixerDeviceSink, Player, Source, cpal::BufferSize, source::Amplify,
+};
 use std::{fs::File, io::BufReader, sync::mpsc::Receiver};
 
 #[derive(Debug)]
@@ -6,8 +8,10 @@ pub enum AudioCmd {
     Mute,
     VolumeUp,
     VolumeDown,
+    ChangePart(SoundrackParts),
 }
 
+#[derive(Debug)]
 pub enum SoundrackParts {
     Calm,
     Buildup,
@@ -15,7 +19,7 @@ pub enum SoundrackParts {
     Outro,
 }
 
-fn load_audio(part: SoundrackParts) -> Amplify<Decoder<BufReader<File>>> {
+fn load_audio(part: &SoundrackParts) -> Amplify<Decoder<BufReader<File>>> {
     let file: File = match part {
         SoundrackParts::Calm => File::open("soundtrack/default/test.ogg").expect("open audio file"),
         SoundrackParts::Buildup => {
@@ -35,36 +39,33 @@ fn load_audio(part: SoundrackParts) -> Amplify<Decoder<BufReader<File>>> {
 }
 
 pub fn handle_audio(rx: Receiver<AudioCmd>, mute: bool) {
-    let mut handle: MixerDeviceSink =
-        DeviceSinkBuilder::open_default_sink().expect("open default audio stream");
-
+    let mut handle: MixerDeviceSink = DeviceSinkBuilder::from_default_device()
+        .expect("get default device")
+        .with_buffer_size(BufferSize::Fixed(4096))
+        .open_sink_or_fallback()
+        .expect("open device audio stream");
     handle.log_on_drop(false);
 
     let player: Player = Player::connect_new(&handle.mixer());
 
     let mut volume: f32 = player.volume();
+    player.set_volume(if mute { 0.0 } else { volume });
 
-    if mute {
-        player.set_volume(0.0);
-    } else {
-        player.set_volume(volume);
-    }
+    // let preloaded_soundtrack_files: [File; 4] = [
+    //     File::open("soundtrack/default/test.ogg").expect("open audio file"),
+    //     File::open("soundtrack/default/test.ogg").expect("open audio file"),
+    //     File::open("soundtrack/default/test.ogg").expect("open audio file"),
+    //     File::open("soundtrack/default/test.ogg").expect("open audio file"),
+    // ];
 
-    player.append(load_audio(SoundrackParts::Calm));
+    let mut current_part: SoundrackParts = SoundrackParts::Calm;
+    player.append(load_audio(&current_part));
 
     loop {
-        if player.empty() {
-            player.append(load_audio(SoundrackParts::Calm));
-        }
-
         for cmd in rx.try_iter() {
             match cmd {
                 AudioCmd::Mute => {
-                    if player.volume() == 0.0 {
-                        player.set_volume(volume);
-                    } else {
-                        player.set_volume(0.0);
-                    }
+                    player.set_volume(if player.volume() == 0.0 { volume } else { 0.0 });
                 }
                 AudioCmd::VolumeUp => {
                     volume = (volume + 0.1).min(1.0);
@@ -74,7 +75,16 @@ pub fn handle_audio(rx: Receiver<AudioCmd>, mute: bool) {
                     volume = (volume - 0.1).max(0.0);
                     player.set_volume(volume);
                 }
+                AudioCmd::ChangePart(part) => {
+                    current_part = part;
+                    player.append(load_audio(&current_part));
+                    player.skip_one();
+                }
             }
         }
+
+        if player.empty() {
+            player.append(load_audio(&current_part));
+        }
     }
 }