Make pre-commit hook work properly

hooks/pre-commit.hook

@@ -1,3 +1,37 @@
 #!/bin/bash
-cd AfRApay.MateCard
-uncrustify --no-backup -c .uncrustify.cfg src/*.cpp include/*.h
+
+# Regexp for grep to only choose some file extensions for formatting
+exts="\.\(cpp\|h\)$"
+
+# The formatter to use
+formatter=`which uncrustify`
+
+# Check availability of the formatter
+if [ -z "$formatter" ]
+then
+  1>&2 echo "$formatter not found. Pre-commit formatting will not be done."
+  exit 0
+fi
+
+# Format staged files
+for file in `git diff --cached --name-only --diff-filter=ACMR | grep $exts`
+do
+  echo "Formatting $file"
+  # Get the file from index
+  git show ":$file" > "$file.tmp"
+  # Format it
+  "$formatter" --no-backup -c AfRApay.MateCard/.uncrustify.cfg "$file.tmp"
+  # Create a blob object from the formatted file
+  hash=`git hash-object -w "$file.tmp"`
+  # Add it back to index
+  git update-index --add --cacheinfo 100644 "$hash" "$file"
+  # Remove the tmp file
+  rm "$file.tmp"
+done
+
+# If no files left in index after formatting - fail
+ret=0
+if [ ! "`git diff --cached --name-only`" ]; then
+  1>&2 echo "No files left after formatting"
+  exit 1
+fi