Refactor the imp/gui bondary to use real traits (#18)

# Summary

Introduces a trait-based platform abstraction layer that makes the boundary
between platform-specific and shared code explicit and compile-time verified.

The TLDR version of this new trait stuff works:

1. Define a `PlatformInterface` trait.
2. Each platform defines a zero-sized struct implementing the trait (ex `WebPlatform`).
3. Create an ifdef'd type alias on those structs:

```rust
#[cfg(feature = "web")]
pub type Platform = web::WebPlatform;

#[cfg(all(feature = "desktop"))]
pub type Platform = desktop::DesktopPlatform;

#[cfg(all(feature = "mobile", not(feature = "web")))]
pub type Platform = mobile::MobilePlatform;
```

5. Add a compile time assertion that `Platform` implements `PlatformInterface`.

#  Motivation

Previously, platform code used a mix of pub use re-exports and #[cfg] blocks
that made it difficult to understand what each platform must implement. The
new trait-based approach provides:

- Clear documentation of the platform contract
- Compile-time verification that all platforms implement required
  functionality
- Ability to cargo check without feature flags (via stub platform)

# Changes

New traits in imp/mod.rs:
  - PlatformInterface - logging, permissions, network, config, storage. Overall this the trait that platforms must satify to compile.
  - AudioSystemInterface - audio system initialization and recording
  - AudioPlayerInterface - opus audio playback

 Type aliases:
  - Platform, AudioSystem, AudioPlayer resolve to the correct types based on
  feature flags

Call site updates:
  - Changed from imp::function() to Platform::function() syntax
  - Removed ImpRead/ImpWrite helper traits in favor of direct bounds

# Testing

Manual testing reveals that Web and Desktop still work, I (Liam) have not tested the mobile version beyond compilation.

Co-authored-by: Liam Warfield <liam.warfield@gmail.com>
Reviewed-on: #18
Co-authored-by: Sam Sartor <me@samsartor.com>
Co-committed-by: Sam Sartor <me@samsartor.com>

gui/src/imp/web.rs

@@ -3,7 +3,6 @@ use crate::effects::{AudioProcessor, AudioProcessorSender, TransmitState};
 use color_eyre::eyre::{bail, eyre, Error};
 use crossbeam::atomic::AtomicCell;
 use dioxus::prelude::*;
-use futures::{AsyncRead, AsyncWrite};
 use gloo_timers::future::TimeoutFuture;
 use js_sys::Float32Array;
 use mumble_protocol::control::ClientControlCodec;
@@ -29,7 +28,6 @@ use web_sys::AudioWorkletNode;
 use web_sys::EncodedAudioChunk;
 use web_sys::EncodedAudioChunkInit;
 use web_sys::EncodedAudioChunkType;
-use web_sys::MediaStream;
 use web_sys::MediaStreamConstraints;
 use web_sys::MessageEvent;
 use web_sys::WebTransport;
@@ -39,16 +37,119 @@ use web_sys::WorkletOptions;
 use web_sys::{console, window};
 use web_sys::{AudioContext, AudioDataCopyToOptions};
 
+#[allow(unused)]
 pub use wasm_bindgen_futures::spawn_local as spawn;
 
-pub trait ImpRead: AsyncRead + Unpin + 'static {}
-impl<T: AsyncRead + Unpin + 'static> ImpRead for T {}
+#[allow(unused)]
+#[derive(Clone)]
+pub struct SpawnHandle;
 
-pub trait ImpWrite: AsyncWrite + Unpin + 'static {}
-impl<T: AsyncWrite + Unpin + 'static> ImpWrite for T {}
+impl SpawnHandle {
+    pub fn spawn<F>(&self, future: F)
+    where
+        F: Future<Output = ()> + 'static,
+    {
+        wasm_bindgen_futures::spawn_local(future);
+    }
 
-pub async fn sleep(d: Duration) {
-    TimeoutFuture::new(d.as_millis() as u32).await
+    pub fn current() -> Self {
+        SpawnHandle
+    }
+}
+
+/// Web platform implementation using WebTransport and Web Audio API.
+pub struct WebPlatform;
+
+impl super::PlatformInterface for WebPlatform {
+    type AudioSystem = WebAudioSystem;
+
+    fn init_logging() {
+        // copied from tracing_web example usage
+
+        use tracing_subscriber::fmt::format::Pretty;
+        use tracing_subscriber::prelude::*;
+        use tracing_web::{performance_layer, MakeWebConsoleWriter};
+
+        let fmt_layer = tracing_subscriber::fmt::layer()
+            .with_ansi(false) // Only partially supported across browsers
+            .without_time() // std::time is not available in browsers
+            .with_writer(MakeWebConsoleWriter::new()) // write events to the console
+            .with_filter(LevelFilter::DEBUG);
+        let perf_layer = performance_layer().with_details_from_fields(Pretty::default());
+
+        tracing_subscriber::registry()
+            .with(fmt_layer)
+            .with(perf_layer)
+            .init();
+
+        info!("logging initiated");
+    }
+
+    fn request_permissions() {
+        // No-op on web
+    }
+
+    async fn load_config() -> color_eyre::Result<ClientConfig> {
+        let config_url = match option_env!("MUMBLE_WEB2_GUI_CONFIG_URL") {
+            Some(url) => Url::parse(url)?,
+            None => absolute_url("config")?,
+        };
+        info!("loading config from {}", config_url);
+
+        let config = reqwest::get(config_url)
+            .await?
+            .json::<ClientConfig>()
+            .await?;
+
+        Ok(config)
+    }
+
+    fn load_username() -> Option<String> {
+        web_sys::window()
+            .unwrap()
+            .local_storage()
+            .ok()??
+            .get_item("username")
+            .ok()?
+    }
+
+    fn load_server_url() -> Option<String> {
+        None
+    }
+
+    fn set_default_username(username: &str) -> Option<()> {
+        web_sys::window()?
+            .local_storage()
+            .ok()??
+            .set_item("username", username)
+            .ok()
+    }
+
+    fn set_default_server(_server: &str) -> Option<()> {
+        None
+    }
+
+    async fn network_connect(
+        address: String,
+        username: String,
+        event_rx: &mut UnboundedReceiver<Command>,
+        gui_config: &ClientConfig,
+    ) -> Result<(), Error> {
+        network_connect(address, username, event_rx, gui_config).await
+    }
+
+    async fn get_status(client: &reqwest::Client) -> color_eyre::Result<ServerStatus> {
+        Ok(client
+            .get(absolute_url("status")?)
+            .send()
+            .await?
+            .json::<ServerStatus>()
+            .await?)
+    }
+
+    async fn sleep(duration: Duration) {
+        TimeoutFuture::new(duration.as_millis() as u32).await;
+    }
 }
 
 trait ResultExt<T> {
@@ -73,7 +174,7 @@ impl<T> ResultExt<T> for Result<T, JsError> {
     }
 }
 
-pub struct AudioSystem {
+pub struct WebAudioSystem {
     webctx: AudioContext,
     processors: AudioProcessorSender,
 }
@@ -104,8 +205,10 @@ async fn attach_worklet(audio_context: &AudioContext) -> Result<(), Error> {
     Ok(())
 }
 
-impl AudioSystem {
-    pub async fn new() -> Result<Self, Error> {
+impl super::AudioSystemInterface for WebAudioSystem {
+    type AudioPlayer = WebAudioPlayer;
+
+    async fn new() -> Result<Self, Error> {
         // Create MediaStreams to playback decoded audio
         // The audio context is used to reproduce audio.
         let webctx = configure_audio_context();
@@ -113,17 +216,14 @@ impl AudioSystem {
 
         let processors = AudioProcessorSender::default();
 
-        Ok(AudioSystem { webctx, processors })
+        Ok(WebAudioSystem { webctx, processors })
     }
 
-    pub fn set_processor(&self, processor: AudioProcessor) {
+    fn set_processor(&self, processor: AudioProcessor) {
         self.processors.store(Some(processor))
     }
 
-    pub fn start_recording(
-        &mut self,
-        each: impl FnMut(Vec<u8>, bool) + 'static,
-    ) -> Result<(), Error> {
+    fn start_recording(&mut self, each: impl FnMut(Vec<u8>, bool) + 'static) -> Result<(), Error> {
         let audio_context_worklet = self.webctx.clone();
         let processors = self.processors.clone();
         spawn(async move {
@@ -135,7 +235,7 @@ impl AudioSystem {
         Ok(())
     }
 
-    pub fn create_player(&mut self) -> Result<AudioPlayer, Error> {
+    fn create_player(&mut self) -> Result<WebAudioPlayer, Error> {
         let sink_node = AudioWorkletNode::new(&self.webctx, "rust_speaker_worklet").ey()?;
 
         // Connect worklet to destination
@@ -188,14 +288,14 @@ impl AudioSystem {
         decoder_error.forget();
         output.forget();
 
-        Ok(AudioPlayer(audio_decoder))
+        Ok(WebAudioPlayer(audio_decoder))
     }
 }
 
-pub struct AudioPlayer(AudioDecoder);
+pub struct WebAudioPlayer(AudioDecoder);
 
-impl AudioPlayer {
-    pub fn play_opus(&mut self, payload: &[u8]) {
+impl super::AudioPlayerInterface for WebAudioPlayer {
+    fn play_opus(&mut self, payload: &[u8]) {
         let js_audio_payload = Uint8Array::from(payload);
         let _ = self.0.decode(
             &EncodedAudioChunk::new(&EncodedAudioChunkInit::new(
@@ -418,94 +518,8 @@ pub async fn network_connect(
     crate::network_loop(username, event_rx, reader, writer).await
 }
 
-pub fn set_default_username(username: &str) -> Option<()> {
-    web_sys::window()?
-        .local_storage()
-        .ok()??
-        .set_item("username", username)
-        .ok()
-}
-
-pub fn set_default_server(username: &str) -> Option<()> {
-    None
-}
-
-pub fn load_username() -> Option<String> {
-    web_sys::window()
-        .unwrap()
-        .local_storage()
-        .ok()??
-        .get_item("username")
-        .ok()?
-}
-
-pub fn load_server_url() -> Option<String> {
-    None
-}
-
 pub fn absolute_url(path: &str) -> Result<Url, Error> {
     let window: web_sys::Window = web_sys::window().expect("no global `window` exists");
     let location = window.location();
     Ok(Url::parse(&location.href().ey()?)?.join(path)?)
 }
-
-pub async fn load_config() -> color_eyre::Result<ClientConfig> {
-    let config_url = match option_env!("MUMBLE_WEB2_GUI_CONFIG_URL") {
-        Some(url) => Url::parse(url)?,
-        None => absolute_url("config")?,
-    };
-    info!("loading config from {}", config_url);
-
-    let config = reqwest::get(config_url)
-        .await?
-        .json::<ClientConfig>()
-        .await?;
-
-    Ok(config)
-}
-
-pub async fn get_status(client: &reqwest::Client) -> color_eyre::Result<ServerStatus> {
-    Ok(client
-        .get(absolute_url("status")?)
-        .send()
-        .await?
-        .json::<ServerStatus>()
-        .await?)
-}
-
-pub fn init_logging() {
-    // copied from tracing_web example usage
-
-    use tracing_subscriber::fmt::format::Pretty;
-    use tracing_subscriber::prelude::*;
-    use tracing_web::{performance_layer, MakeWebConsoleWriter};
-
-    let fmt_layer = tracing_subscriber::fmt::layer()
-        .with_ansi(false) // Only partially supported across browsers
-        .without_time() // std::time is not available in browsers
-        .with_writer(MakeWebConsoleWriter::new()) // write events to the console
-        .with_filter(LevelFilter::DEBUG);
-    let perf_layer = performance_layer().with_details_from_fields(Pretty::default());
-
-    tracing_subscriber::registry()
-        .with(fmt_layer)
-        .with(perf_layer)
-        .init();
-
-    info!("logging initiated");
-}
-
-pub struct SpawnHandle;
-
-impl SpawnHandle {
-    pub fn current() -> Self {
-        SpawnHandle
-    }
-
-    pub fn spawn<F>(&self, future: F)
-    where
-        F: Future<Output = ()> + 'static,
-    {
-        spawn(future);
-    }
-}