#!/bin/sh -e
# convert twtxt.txt to atom file
# 09/05 : make sha256 usable on linux. Thanks Frederic Galusik.

# some help can't hurt
help() 
{
	printf "usage:\n"
	printf "\t%s -n <nick> -u <feed url> -t <feed title> -x <twtxt.txt url> twtxt.txt\n" "$0"
	exit 1
}

# make sure variables to check later if user set them
nick=""
url=""
title=""
twtxturl=""

# use getopt to get options
while getopts 'n:u:t:x:h' c
do
	case $c in
		n) nick="${OPTARG}" ;;
		u) url="${OPTARG}" ;;
		t) title="${OPTARG}" ;;
		x) twtxturl="${OPTARG}" ;;
		h) help ;;
	esac
done
# skip options in argumnent index so $1 is twtxt.txt
shift $((OPTIND - 1))

# abort if user forgot a parameter
test -z "$nick" && help
test -z "$url" && help
test -z "$title" && help

# header template of the atom
HEADER="<?xml version='1.0' encoding='utf-8'?>
<feed xmlns='http://www.w3.org/2005/Atom'>
<id>${url}</id>
<title>${title}</title>
<link rel='self' type='application/atom+xml' href='${url}' />
<author><name>${nick}</name></author>
"

# get the last entry to set last time atom was updated
LAST="$(awk 'END {print $1}' $1)"

# Let's output the beginning
printf '%s' "$HEADER"
printf '<updated>%s</updated>\n' "$LAST"

# grep remove comments and empty lines and loop over twtxt.txt lines
grep -Ev '^#|^$' "${1}" | while read -r TS MSG; do
	# ID must be unique, use sha256 on it
	if [[ "$OSTYPE" == "linux-gnu" ]]; then
		ID="$(printf '%s' "$1 $TS $MSG" | sha256sum | cut -f 1 -d " " )"
	else
		ID="$(printf '%s' "$1 $TS $MSG" | sha256)"
	fi
	# Can't have ]]> in CDATA
	ESCAPED="$(printf "%s" "${MSG}" | awk '{gsub("]]>", "]]]]><![CDATA[>")}1')"
	# output the entry
	printf '<entry>\n'
	printf '<id>urn:hash::sha256:%s</id>\n' "${ID}"
	printf '<title type="text"><![CDATA[%s]]></title>\n' "${ESCAPED}"
	printf '<updated>%s</updated>\n' "${TS}"
	printf '<content type="text"><![CDATA[%s]]></content>\n' "${ESCAPED}"
	printf '<link rel="alternate" type="text/plain" href="%s" />\n' "${twtxturl}"
	printf '</entry>\n'
done

printf '%s' '</feed>' 
exit 0