Added code to copy song

src/song.rs

@@ -153,6 +153,7 @@ impl Song {
         filename
     }
 
+    /// Saves the song to the filesystem using the song's data
     pub fn save_to_filesystem(&self) -> Result<(), std::io::Error> {
         match self.song_path() {
             Ok(song_path) => match std::fs::File::create(&song_path) {
@@ -169,4 +170,29 @@ impl Song {
     // TODO: Add function to remove file from the filesystem
 }
 
-// TODO: Add function to copy song
+/// Copies a song using the source song's data
+pub fn copy_song(song_source: &Song, song_target: &mut Song) -> Result<(), std::io::Error> {
+    match song_target.song_path() {
+        Ok(songpath) => {
+            let p = std::path::Path::new(&songpath);
+            if p.exists() {
+                Err(std::io::Error::other(
+                    "Cannot copy song over to one that already exists",
+                ))
+            } else {
+                if song_target.data.is_empty() {
+                    song_target.data = song_source.data.clone();
+                } else {
+                    song_target.data.clear();
+                    song_target.data = song_source.data.clone();
+                }
+
+                match song_target.save_to_filesystem() {
+                    Ok(_) => Ok(()),
+                    Err(err) => Err(err),
+                }
+            }
+        }
+        Err(err) => Err(err),
+    }
+}