feat: argparse and dry-run.

src/file_finder.rs

@@ -0,0 +1,37 @@
+use std::io::Result;
+use std::path::{Path, PathBuf};
+
+pub fn find_largest_video_file(path: &Path) -> Result<PathBuf> {
+    let mut largest_size = 0;
+    let mut largest_file = PathBuf::from(path);
+    for entry in std::fs::read_dir(path)? {
+        let entry_path = entry?.path().canonicalize()?;
+        if entry_path.is_dir() {
+            continue;
+        }
+
+        let size = entry_path.metadata()?.len();
+        if size >= largest_size {
+            largest_size = size;
+            largest_file = entry_path.into();
+        }
+    }
+
+    Ok(largest_file)
+}
+
+pub fn find_audio_file(video_path: &Path) -> Result<PathBuf> {
+    let video_name = video_path.file_name().unwrap().to_str().unwrap();
+    let video_extension = video_path.extension().unwrap();
+    let audio_name = format!("{}.m4a", &video_name[..video_name.len() - video_extension.len() - 1]);
+    let audio_path = video_path.parent().unwrap().join(audio_name);
+
+    if !audio_path.exists() {
+        return Err(std::io::Error::new(
+            std::io::ErrorKind::NotFound,
+            format!("Audio file does not exist: {}", audio_path.display())
+        ));
+    }
+
+    Ok(audio_path)
+}