#!/usr/bin/env bash
set -u
set -e

ref_name=$1
old_rev=$2
new_rev=$3

# Here you can use whatever formatter you like
# and set up the error (or success) output as you wish
format() {
	local my_work_tree=$1
	pushd $my_work_tree >/dev/null

	# briefly allow non-zero exit status
	set +e
	local my_diffs=$(2>&1 /usr/local/bin/prettier './**/*.{js,css,html,json,md}' --list-different | grep -v 'No matching files')
	set -e

	# Show a friendly error message to the git user downstream (if there are files to fix)
	if [ -n "$my_diffs" ]; then
		>&2 echo ""
		>&2 echo "Please run prettier on the following files (and double check your .prettierrc):"
		echo "$my_diffs" | while read my_word; do
			>&2 echo "	$my_word"
		done
		>&2 echo ""
		>&2 echo "Example:"
		>&2 echo "	npm install -g prettier"
		>&2 echo "	prettier './**/*.{js,css,html,json,md}' --write"
		>&2 echo ""
	fi

	popd >/dev/null

	# This is the "return" value
	echo $my_diffs
}

# This is all pretty generic - just checking out files to lint/format and running said formatter
case "${ref_name}" in
refs/heads/*)
	# match empty commit 0000000000000000000000000000000000000000
	# all deletes should be successful (no files to check against)
	if [ "$(expr "${new_rev}" : '0*$')" -ne 0 ]; then
		exit 0
	fi

	# We don't want a race condition if multiple people push while a check is in progress
	# For this reason we first checkout all of the files in HEAD and the copy over the changed files.
	# We also need to remove any deleted files.
	#
	# ex: /tmp/git-work-tree.abc123xyz
	my_work_tree=$(mktemp -d -t git-work-tree.XXXXXXXX) 2>/dev/null
	if [ "$(expr "${old_rev}" : '0*$')" -ne 0 ]; then
		# Ignore "fatal: You are on a branch yet to be born"
		set +e
	fi
	git --work-tree="${my_work_tree}" --git-dir="." checkout -f >/dev/null
	my_changes=$(git --work-tree="${my_work_tree}" --git-dir="." diff --name-status HEAD $new_rev)
	if [ -n "$(echo "$my_changes" | grep -e "^A")" ]; then
		echo "$my_changes" | grep -e "^A" | cut -f 2 | \
			xargs git --work-tree="${my_work_tree}" --git-dir="." checkout $new_rev --
	fi
	if [ -n "$(echo "$my_changes" | grep -e "^M")" ]; then
		echo "$my_changes" | grep -e "^M" | cut -f 2 | \
			xargs git --work-tree="${my_work_tree}" --git-dir="." checkout $new_rev --
	fi
	if [ -n "$(echo "$my_changes" | grep -e "^D")" ]; then
		echo "$my_changes" | grep -e "^D" | cut -f 2 | \
			xargs git --work-tree="${my_work_tree}" --git-dir="." rm -rf -- >/dev/null
	fi

	# Now we run the formatter, do some cleanup, and error out if needed
	my_failure=$(format $my_work_tree)
	rm -rf "${my_work_tree}"
	if [ -n "$my_failure" ]; then
		exit 1
	fi
;;
refs/tags/*)
	# allowing tags to be made regardless of formatting (such as old versions)
	exit 0
;;
*)
	# allowing all other things (not sure what they are though, TBH)
	exit 0
;;
esac