#!/usr/bin/env bash
#
# A hook script to check the commit log message.
# Called by "git commit" with one argument, the name of the file that has the
# commit message.
# The hook should exit with non-zero status after issuing an appropriate message
# if it wants to stop the commit.
# The hook is allowed to edit the commit message file.
#
# To enable this hook, save this file in ".git/hooks/commit-msg".

die() {
	printf "$1" >&2
	exit ${2:-1}
}

subject="$(head -1 "$1")"
# Ignore "fixup! " and "squash! " prefix' added by `git-commit`
subject="${subject#fixup! }"
subject="${subject#squash! }"

# git's character to comment out lines in commit messages. The `auto` value is
# handled specially (see the different uses of $git_comment_char).
# NOTE: Only `^` is escaped as $git_comment_char is used in character classes
#       and thus all other characters are free to use.
git_comment_char="$(git config --get --default='#' core.commentChar \
                    | sed 's:\^:\\&:g')"
# git's cut-line to cut off everything behind it (e.g. commit patch with
# `commit.verbose`)
cut_line='------------------------ >8 ------------------------'

# Take all lines after the subject until EOF or the cut-line (here `auto` is
# replaced with 'any character' as the cut-line in itself should hopefully be
# unambiguous enough) and remove all lines starting with the comment-char
# (`auto` is not handled properly but rather replaced with the default `#`)
body="$(
	tail +2 "$1" \
	| sed -n "/^[${git_comment_char/auto/[:print:]\t}] $cut_line\$/q
	          /^[^${git_comment_char/auto/\#}]/p"
)"

[[ ${#subject} -le 50 ]] || die "Subject too long. (<= 50)\n"

# The subject line has to match "${pats[@]}", but to be more verbose different
# error messages are printed for the different 'levels' of the pattern.
declare -a pats msg
pats=(
	"^([-_,*(){}./a-zA-Z0-9]+:)+ "
	"[A-Z]"
	".*[^.]$"
)
msg=(
	"Specify which program was modified. (e.g. \"zsh:p10k: <subject>\")\n"
	"Start subject with a capital letter.\n"
	"Remove punctuation mark from end.\n"
)
[[ ${#msg[@]} -ge ${#pats[@]} ]] || die "Something went wrong internally.\n"
for ((i = 0; i < ${#pats[@]}; i++)); do
	if ! grep -qE "$(printf "%s" "${pats[@]:0:$i+1}")" <<<"$subject"; then
		die "${msg[$i]}"
	fi
done

BKP_IFS="$IFS"
IFS='
'
for line in $body; do
	[[ ${#line} -le 72 ]] || die "Body lines too long. (<= 72)\n"
done
IFS="$BKP_IFS"