add command line args support

src/main.rs

@@ -1,11 +1,42 @@
 use crate::line::Line;
+use clap::Parser;
 use std::fs::read_to_string;
+use std::process::exit;
 
 mod line;
 
+#[derive(Parser, Debug)]
+#[command(
+    version = "0.1",
+    about = "A simple toy program to compare file differences.",
+    long_about = "A simple toy program to compare file differences. Written as an exercise to learn Rust and its ecosystem."
+)]
+struct CliArgs {
+    /// The path to the left file to be compared.
+    left_file_path: String,
+
+    /// The path to the right file to be compared.
+    right_file_path: String,
+}
+
 fn main() {
-    let left_file = read_to_string("a.txt").expect("Left file not found");
-    let right_file = read_to_string("b.txt").expect("Right file not found");
+    let args = CliArgs::parse();
+
+    let left_file = match read_to_string(&args.left_file_path) {
+        Ok(right_file) => right_file,
+        Err(_) => {
+            eprintln!("ERROR: File {} was not found.", &args.left_file_path);
+            exit(1)
+        }
+    };
+
+    let right_file = match read_to_string(&args.right_file_path) {
+        Ok(right_file) => right_file,
+        Err(_) => {
+            eprintln!("ERROR: File {} was not found.", &args.right_file_path);
+            exit(1)
+        }
+    };
 
     let lines: Vec<Line> = line::compare_lines(&left_file, &right_file);