Update to not recompile if code hasn't changed

src/app.rs

@@ -245,6 +245,22 @@ fn build(mode: &Option<String>) -> std::io::Result<()> {
 
     std::fs::create_dir_all(format!("target/{}", build_config.name))?;
 
+    let hash = hash_src_tree()?;
+
+    let old_compute_path = PathBuf::from(format!("target/{}/.build_hash", build_config.name));
+
+    if old_compute_path.exists() {
+        let text = std::fs::read_to_string(old_compute_path)?;
+
+        if hash.trim() == text.trim() {
+            println!(
+                "   {} (code not changed, recompile not made)",
+                "Finished".green().bold()
+            );
+            return Ok(());
+        }
+    }
+
     let mut command = Command::new("gcc");
 
     for arg in &build_config.args {
@@ -280,6 +296,18 @@ fn build(mode: &Option<String>) -> std::io::Result<()> {
     Ok(())
 }
 
+fn hash_src_tree() -> std::io::Result<String> {
+    let mut hashes = String::new();
+    for entry in glob("src/").expect("a valid glob pattern") {
+        if let Ok(file) = entry {
+            let text = std::fs::read_to_string(file)?;
+            let hash = sha256::digest(text);
+            hashes.push_str(hash.as_str());
+        }
+    }
+    Ok(sha256::digest(hashes))
+}
+
 fn run(mode: &Option<String>, args: Option<Vec<String>>) -> std::io::Result<()> {
     let conf = match get_config() {
         Some(conf) => conf,