Fixed hooks

hooks/pre-commit

@@ -1,4 +1,12 @@
-git_dir=$(git rev-parse --git-dir)
-project_dir=$(dirname $git_dir)
+#!/bin/sh
+# adapted from https://prettier.io/docs/en/precommit.html#option-5-shell-script
+FILES=$(git diff --cached --name-only --diff-filter=ACMR | sed 's| |\\ |g' | grep '.dart$')
+[ -z "$FILES" ] && exit 0
 
-dart format $project_dir
+# Format all selected files
+echo "$FILES" | xargs dart format
+
+# Add back the formatted files to staging
+echo "$FILES" | xargs git add
+
+exit 0