Remember about the microphone device last selected by the user when opening the application, as suggested by issue #3

Author: marin-m

README.md

@@ -98,6 +98,8 @@ The following will produce back hearable tones from a given fingerprint, that sh
 ./songrec fingerprint-to-lure 'data:audio/vnd.shazam.sig;base64,...' /tmp/output.wav
 ```
 
+When using the application, you may notice that certain information will be savec to `~/.local/share/SongRec` (or an equivalent directory depending on your operating system), including the CSV-format list of the last recognized songs and the last selected microphone input device (so that it is chosen back when restarting the app). You may want to delete this directory in case of persistent issues.
+
 ## Legal
 
 This software is released under the [GNU GPL v3](https://www.gnu.org/licenses/gpl-3.0.html) license. It was created with the intent of providing interoperability between the remote Shazam services and Linux-based deskop systems.

src/gui/main_window.rs

@@ -1,6 +1,8 @@
 use gio::prelude::*;
 use glib::clone;
 use gtk::prelude::*;
+use std::fs::File;
+use std::io::{Read, Write};
 use gtk::ResponseType;
 use gdk_pixbuf::Pixbuf;
 use std::error::Error;
@@ -110,6 +112,20 @@ pub fn gui_main(recording: bool) -> Result<(), Box<dyn Error>> {
         let current_signature: Rc<RefCell<Option<DecodedSignature>>> = Rc::new(RefCell::new(None));
         let current_signature_2 = current_signature.clone();
 
+        // Remember about the saved last-used microphone device, if any
+
+        let device_name_savefile = SongHistoryInterface::obtain_csv_path().unwrap()
+            .replace("song_history.csv", "device_name.txt");
+        
+        let mut old_device_name: Option<String> = None;
+        
+        if let Ok(mut file) = File::open(&device_name_savefile) {
+            let mut old_device_name_string = String::new();
+            file.read_to_string(&mut old_device_name_string).unwrap();
+            
+            old_device_name = Some(old_device_name_string);
+        }
+        
         // List available input microphones devices in the appropriate combo box
 
         let combo_box: gtk::ComboBox = builder.get_object("microphone_source_select_box").unwrap();
@@ -124,21 +140,43 @@ pub fn gui_main(recording: bool) -> Result<(), Box<dyn Error>> {
         // through disabling stderr temporarily
 
         let print_gag = Gag::stderr().unwrap();
+        let mut old_device_index = 0;
+        let mut current_index = 0;
 
         for device in host.input_devices().unwrap() {
-            combo_box_model.set(&combo_box_model.append(), &[0], &[&device.name().unwrap()]);
+            let device_name = device.name().unwrap();
+            
+            combo_box_model.set(&combo_box_model.append(), &[0], &[&device_name]);
+            
+            if old_device_name == Some(device_name) {
+                old_device_index = current_index;
+            }
+            current_index += 1;
         }
 
         drop(print_gag);
 
-        combo_box.set_active(Some(0));
+        combo_box.set_active(Some(old_device_index));
 
         combo_box.connect_changed(clone!(@weak microphone_stop_button, @weak combo_box => move |_| {
 
+            let device_name = combo_box.get_active_id().unwrap().to_string();
+            
+            // Save the selected microphone device name so that it is
+            // remembered after relaunching the app
+            
+            let mut file = File::create(&device_name_savefile).unwrap();
+            
+            file.write_all(device_name.as_bytes()).unwrap();
+            file.sync_all().unwrap();
+            
+            drop(file);
+            
             if microphone_stop_button.is_visible() {
 
-                let device_name = combo_box.get_active_id().unwrap().to_string();
-             
+                // Re-launch the microphone recording with the new selected
+                // device
+                
                 microphone_tx_4.send(MicrophoneMessage::MicrophoneRecordStop).unwrap();
                 microphone_tx_4.send(MicrophoneMessage::MicrophoneRecordStart(device_name)).unwrap();