Move standalone backends to their own modules

src/wrapper/standalone/backend/jack.rs

@@ -0,0 +1,36 @@
+use anyhow::{Context, Result};
+use jack::{Client, ClientOptions};
+
+use super::super::config::WrapperConfig;
+use super::Backend;
+use crate::buffer::Buffer;
+
+/// Uses JACK audio and MIDI.
+pub struct Jack {
+    config: WrapperConfig,
+    client: Client,
+}
+
+impl Backend for Jack {
+    fn run(&mut self, cb: impl FnMut(&mut Buffer) -> bool) {
+        // TODO: Create an async client and do The Thing (tm)
+        todo!()
+    }
+}
+
+impl Jack {
+    /// Initialize the JACK backend. Returns an error if this failed for whatever reason.
+    pub fn new(name: &str, config: WrapperConfig) -> Result<Self> {
+        let (client, status) = Client::new(name, ClientOptions::NO_START_SERVER)
+            .context("Error while initializing the JACK client")?;
+        if !status.is_empty() {
+            anyhow::bail!("The JACK server returned an error: {status:?}");
+        }
+
+        // TODO: Register ports
+        // TODO: Connect output
+        // TODO: Command line argument to connect the inputs?
+
+        Ok(Self { config, client })
+    }
+}