feat: add cpal-based auto device detection and configuration

3 files changed, 84 insertions, 19 deletions

diff --git a/src/args.rs b/src/args.rs
index 9a4bd0d..1f0b7df 100644
--- a/src/args.rs
+++ b/src/args.rs
@@ -69,7 +69,8 @@ pub struct DMVOPArguments {
         long = "device",
         alias = "dev",
         allow_hyphen_values = true,
-        require_equals = true
+        require_equals = true,
+        default_value = "auto"
     )]
     pub device_name: Option<String>,
 
diff --git a/src/device_selector.rs b/src/device_selector.rs
new file mode 100644
index 0000000..12f8a79
--- /dev/null
+++ b/src/device_selector.rs
@@ -0,0 +1,78 @@
+use cpal::traits::{DeviceTrait, HostTrait};
+
+/// Pick the best input device from the available list.
+///
+/// - `"auto"` → query OS default input device via cpal, match against list
+/// - `"<name>"` → match by device ID or name; exits if not found
+/// - `None` → exits with error
+pub fn pick_device<'a>(
+    name: &Option<String>,
+    devices: &'a [vtx_engine::AudioDevice],
+) -> Option<&'a vtx_engine::AudioDevice> {
+    let name = match name {
+        Some(n) if n == "auto" || n.is_empty() => return pick_auto(devices),
+        Some(n) => n.as_str(),
+        None => {
+            eprintln!(
+                "[dmvop] No device specified. Use --device=<name> or --list-devices to see available devices."
+            );
+            std::process::exit(1);
+        }
+    };
+
+    // Try exact match by id or name
+    if let Some(d) = devices.iter().find(|d| d.id == name || d.name == name) {
+        return Some(d);
+    }
+
+    eprintln!(
+        "[dmvop] Device '{}' not found. Use --list-devices to see available devices.",
+        name
+    );
+    std::process::exit(1);
+}
+
+/// Use cpal to find the system's default input device, then match it
+/// against the vtx-engine device list by WASAPI ID.
+fn pick_auto<'a>(devices: &'a [vtx_engine::AudioDevice]) -> Option<&'a vtx_engine::AudioDevice> {
+    let host = cpal::default_host();
+    let device = match host.default_input_device() {
+        Some(d) => d,
+        None => {
+            eprintln!("[dmvop] No default input device found.");
+            return devices.first();
+        }
+    };
+
+    // Get the WASAPI device ID from cpal
+    let cpal_device_id = match device.id() {
+        Ok(id) => id,
+        Err(_) => return devices.first(),
+    };
+    let cpal_raw_id = cpal_device_id.id().to_string();
+
+    // Match against vtx-engine devices by ID (substring — cpal might omit braces)
+    for dev in devices {
+        let dev_id_clean = dev.id.trim_matches('{').trim_matches('}');
+        let cpal_id_clean = cpal_raw_id.trim_matches('{').trim_matches('}');
+        if dev_id_clean.contains(cpal_id_clean) || cpal_id_clean.contains(dev_id_clean) {
+            return Some(dev);
+        }
+    }
+
+    // Fallback: match by name (cpal DeviceId Display includes host:raw_id)
+    let cpal_display = cpal_device_id.to_string().to_lowercase();
+    for dev in devices {
+        if cpal_display.contains(&dev.name.to_lowercase())
+            || dev.name.to_lowercase().contains(&cpal_display)
+        {
+            return Some(dev);
+        }
+    }
+
+    eprintln!(
+        "[dmvop] Default device ({}) not matched, using first available.",
+        cpal_raw_id
+    );
+    devices.first()
+}
diff --git a/src/main.rs b/src/main.rs
index 2aa68ac..87f7657 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -3,7 +3,9 @@ pub mod post_proc;
 mod args;
 pub use args::*;
 
+mod device_selector;
 mod output_protocol;
+
 use clap::Parser;
 use output_protocol::OutputProtocol;
 use std::path::PathBuf;
@@ -220,30 +222,14 @@ async fn main() {
     // ---------------------------------------------------------------
     // Find the requested device and start capture
     // ---------------------------------------------------------------
-    let device_name = match &args.device_name {
-        Some(n) => n.as_str(),
-        None => {
-            eprintln!(
-                "[dmvop] No device specified. Use --device=<name> or --list-devices to see available devices."
-            );
-            std::process::exit(1);
-        }
-    };
-
-    let device = devices
-        .iter()
-        .find(|d| d.id == device_name || d.name == device_name)
-        .or_else(|| devices.first());
+    let device = device_selector::pick_device(&args.device_name, &devices);
 
     match &device {
         Some(d) => {
             debug_log!("[dmvop] Using input device: {} (id: {})", d.name, d.id);
         }
         None => {
-            eprintln!(
-                "[dmvop] Device '{}' not found and no fallback available.",
-                device_name
-            );
+            eprintln!("[dmvop] No input devices found. Make sure a microphone is connected.");
             std::process::exit(1);
         }
     }