Add drag-and-drop support

Fixes #2

src/main.rs

@@ -7,22 +7,31 @@ use clap::Clap;
 #[derive(Clap)]
 struct Args {
     in_file: PathBuf,
-    out_file: PathBuf,
+    out_file: Option<PathBuf>,
 }
 
 fn main() {
     let args = Args::parse();
+    let out_file = args.out_file.clone().unwrap_or_else(|| {
+        let mut out_file = args.in_file.clone();
+        match out_file.extension().map(|x| x.to_str()).flatten() {
+            Some("lvd") => out_file.set_extension("yaml"),
+            Some("yaml") | Some("yml") => out_file.set_extension("lvd"),
+            _ => true
+        };
+        out_file
+    });
 
     match LvdFile::open(&args.in_file) {
         Ok(lvd_file) => {
-            fs::write(&args.out_file, serde_yaml::to_string(&lvd_file).unwrap()).unwrap();
+            fs::write(&out_file, serde_yaml::to_string(&lvd_file).unwrap()).unwrap();
         }
         Err(binrw::Error::BadMagic { pos: 0, .. }) => {
             // Magic doesn't match, is a yaml file
             let contents = fs::read_to_string(&args.in_file).unwrap();
             let lvd_file: LvdFile = serde_yaml::from_str(&contents).unwrap();
 
-            lvd_file.save(&args.out_file).unwrap();
+            lvd_file.save(&out_file).unwrap();
         }
         Err(err) => {
             eprintln!("Error: {:?}", err);