Add option to apply format fix only on changed files (much faster) (#153)

The default version parses a lot of files and takes ~5s on my machine.
This adds an option `-g` to run only on files modified/staged in git.

bin/clang-format-fix

@@ -1,3 +1,26 @@
 #!/bin/bash
 
-find src lib \( -name "*.c" -o -name "*.cpp" -o -name "*.h" -o -name "*.hpp" \) -exec clang-format -style=file -i {} +
+# Configuration: Standard arguments for clang-format
+STYLE_ARGS="-style=file -i"
+
+# --- Main Logic ---
+
+if [[ "$1" == "-g" ]]; then
+    # Mode: Format all modified files (staged and unstaged)
+
+    # Use 'git ls-files' to get a list of all files with pending changes:
+    # --modified: files tracked by git that have been modified (staged or unstaged)
+    # --exclude-standard: ignores files in .gitignore
+    git ls-files --modified --exclude-standard \
+        | grep -E '\.(c|cpp|h|hpp)$' \
+        | xargs -r clang-format $STYLE_ARGS
+
+    # NOTE: We skip the 'git add' step from before.
+    # When running on unstaged files, 'clang-format -i' modifies them
+    # in the working directory, where they remain unstaged (M).
+
+else
+    # Executes original working command directly.
+    find src lib \( -name "*.c" -o -name "*.cpp" -o -name "*.h" -o -name "*.hpp" \) -exec clang-format $STYLE_ARGS {} +
+
+fi