#!/bin/sh
#
# Copy or link this file as ".git/hooks/pre-commit".

# Prepare a copy of the message:
#  - strip comment lines
#  - stop at "diff --git" (git commit -v)
commit_msg="$GIT_DIR/COMMIT_MSG"
sed -n -e '/^#/d' -e '/^diff --git/q' -e 'p;d' "$1" > "$commit_msg"

die() {
	echo 'commit-msg hook failure' 1>&2
	echo '-----------------------' 1>&2
	echo '' 1>&2
	echo "$@" 1>&2
	echo 'To continue editing, run the command
  git commit -e -F '"$commit_msg"'
(assuming your working directory is at the top).' 1>&2
	exit 1
}

#-----------------------------------------------------------------------------
# Check the commit message layout with a simple state machine.

msg_first() {
	len=$(echo -n "$line" | wc -c)
	if test $len -eq 0; then
		# not yet first line
		return
	elif test $len -lt 8; then
		die 'The first line must be at least 8 characters:
--------
'"$line"'
--------
'
	elif test $len -gt 78; then
		die 'The first line may be at most 78 characters:
------------------------------------------------------------------------------
'"$line"'
------------------------------------------------------------------------------
'
	elif echo "$line" | grep "^[	 ]\|[	 ]$" >/dev/null 2>&1; then
		die 'The first line may not have leading or trailing space:
['"$line"']
'
	else
		# first line okay
		state=second
	fi
}

msg_second() {
	if test "x$line" != "x"; then
		die 'The second line must be empty:
'"$line"
	else
		state=rest
	fi
}

msg_rest() {
	false
}

# Pipe commit message into the state machine.
state=first
cat "$commit_msg" |
while IFS='' read line; do
	msg_$state || break
done &&
rm -f "$commit_msg"