#!/bin/sh
# update feeds, merge with old feeds.
# NOTE: assumes "sfeed_*" executables are in $PATH.

# defaults
sfeedpath="$HOME/.sfeed/feeds"

# used for processing feeds concurrently: wait until ${maxjobs} amount of
# feeds are finished at a time.
maxjobs=16

# load config (evaluate shellscript).
# loadconfig(configfile)
loadconfig() {
	# allow to specify config via argv[1].
	if [ "$1" != "" ]; then
		# get absolute path of config file required for including.
		config="$1"
		configpath=$(readlink -f "${config}" 2>/dev/null)
	else
		# default config location.
		config="$HOME/.sfeed/sfeedrc"
		configpath="${config}"
	fi

	# config is loaded here to be able to override $sfeedpath or functions.
	if [ -r "${configpath}" ] && [ ! -d "${configpath}" ]; then
		. "${configpath}"
	else
		printf "Configuration file \"%s\" cannot be read.\n" "${config}" >&2
		echo "See the sfeedrc.example file or the sfeedrc(5) man page for an example." >&2
		die
	fi
}

# log(name, s)
log() {
	printf '[%s] %-50.50s %s\n' "$(date +'%H:%M:%S')" "$1" "$2"
}

# log_error(name, s)
log_error() {
	printf '[%s] %-50.50s %s\n' "$(date +'%H:%M:%S')" "$1" "$2" >&2
	# set error exit status indicator for parallel jobs.
	rm -f "${sfeedtmpdir}/ok"
}

# fetch a feed via HTTP/HTTPS etc.
# fetch(name, url, feedfile)
fetch() {
	# fail on redirects, hide User-Agent, timeout is 15 seconds.
	curl -L --max-redirs 0 -H "User-Agent:" -f -s -m 15 \
		"$2" 2>/dev/null
}

# convert encoding from one encoding to another.
# convertencoding(name, from, to)
convertencoding() {
	if [ "$2" != "" ] && [ "$3" != "" ] && [ "$2" != "$3" ]; then
		iconv -cs -f "$2" -t "$3" 2> /dev/null
	else
		# else no convert, just output.
		cat
	fi
}

# parse and convert input, by default XML to the sfeed(5) TSV format.
# parse(name, feedurl, basesiteurl)
parse() {
	sfeed "$3"
}

# filter fields.
# filter(name, url)
filter() {
	cat
}

# merge raw files: unique sort by id, title, link.
# merge(name, oldfile, newfile)
merge() {
	sort -t '	' -u -k6,6 -k2,2 -k3,3 "$2" "$3" 2>/dev/null
}

# order by timestamp (descending).
# order(name, url)
order() {
	sort -t '	' -k1rn,1 2>/dev/null
}

# internal handler to fetch and process a feed.
# _feed(name, feedurl, [basesiteurl], [encoding])
_feed() {
	name="$1"
	feedurl="$2"
	basesiteurl="$3"
	encoding="$4"

	filename="$(printf '%s' "${name}" | tr '/' '_')"
	sfeedfile="${sfeedpath}/${filename}"
	tmpfeedfile="${sfeedtmpdir}/feeds/${filename}"

	# if file does not exist yet create it.
	[ -e "${sfeedfile}" ] || touch "${sfeedfile}" 2>/dev/null

	if ! fetch "${name}" "${feedurl}" "${sfeedfile}" > "${tmpfeedfile}.fetch"; then
		log_error "${name}" "FAIL (FETCH)"
		return 1
	fi

	# try to detect encoding (if not specified). if detecting the encoding fails assume utf-8.
	[ "${encoding}" = "" ] && encoding=$(sfeed_xmlenc < "${tmpfeedfile}.fetch")

	if ! convertencoding "${name}" "${encoding}" "utf-8" < "${tmpfeedfile}.fetch" > "${tmpfeedfile}.utf8"; then
		log_error "${name}" "FAIL (ENCODING)"
		return 1
	fi
	rm -f "${tmpfeedfile}.fetch"

	# if baseurl is empty then use feedurl.
	if ! parse "${name}" "${feedurl}" "${basesiteurl:-${feedurl}}" < "${tmpfeedfile}.utf8" > "${tmpfeedfile}.tsv"; then
		log_error "${name}" "FAIL (PARSE)"
		return 1
	fi
	rm -f "${tmpfeedfile}.utf8"

	if ! filter "${name}" "${feedurl}" < "${tmpfeedfile}.tsv" > "${tmpfeedfile}.filter"; then
		log_error "${name}" "FAIL (FILTER)"
		return 1
	fi
	rm -f "${tmpfeedfile}.tsv"

	# new feed data is empty: no need for below stages.
	if [ ! -s "${tmpfeedfile}.filter" ]; then
		log "${name}" "OK"
		return 0
	fi

	if ! merge "${name}" "${sfeedfile}" "${tmpfeedfile}.filter" > "${tmpfeedfile}.merge"; then
		log_error "${name}" "FAIL (MERGE)"
		return 1
	fi
	rm -f "${tmpfeedfile}.filter"

	if ! order "${name}" "${feedurl}" < "${tmpfeedfile}.merge" > "${tmpfeedfile}.order"; then
		log_error "${name}" "FAIL (ORDER)"
		return 1
	fi
	rm -f "${tmpfeedfile}.merge"

	# copy
	if ! cp "${tmpfeedfile}.order" "${sfeedfile}"; then
		log_error "${name}" "FAIL (COPY)"
		return 1
	fi
	rm -f "${tmpfeedfile}.order"

	# OK
	log "${name}" "OK"
	return 0
}

# fetch and process a feed in parallel.
# feed(name, feedurl, [basesiteurl], [encoding])
feed() {
	# Job parameters for xargs.
	# Specify fields as a single parameter separated by the NUL separator.
	# These fields are split later by the child process, this allows xargs
	# with empty fields across many implementations.
	printf '%s\037%s\037%s\037%s\037%s\037%s\0' \
		"${config}" "${sfeedtmpdir}" "$1" "$2" "$3" "$4"
}

cleanup() {
	# remove temporary directory with feed files.
	rm -rf "${sfeedtmpdir}"
}

# die(statuscode)
die() {
	statuscode="${1:-1}" # default: exit 1
	# cleanup temporary files etc.
	cleanup
	exit "${statuscode}"
}

sighandler() {
	signo="$1"
	# ignore TERM signal for myself.
	trap -- "" TERM
	# kill all running children >:D
	kill -TERM -$$
}

feeds() {
	printf "Configuration file \"%s\" is invalid or does not contain a \"feeds\" function.\n" "${config}" >&2
	echo "See sfeedrc.example for an example." >&2
	die
}

main() {
	# signal number received for parent.
	signo=0
	# SIGINT: signal to interrupt parent.
	trap -- "sighandler 2" "INT"
	# SIGTERM: signal to terminate parent.
	trap -- "sighandler 15" "TERM"
	# load config file.
	loadconfig "$1"
	# fetch feeds and store in temporary directory.
	sfeedtmpdir="$(mktemp -d "${TMPDIR:-/tmp}/sfeed_XXXXXX")" || die
	mkdir -p "${sfeedtmpdir}/feeds"
	touch "${sfeedtmpdir}/ok" || die
	# make sure path exists.
	mkdir -p "${sfeedpath}"

	# print feeds for parallel processing with xargs.
	feeds > "${sfeedtmpdir}/jobs" || die
	SFEED_UPDATE_CHILD="1" xargs -x -0 -P "${maxjobs}" -n 1 \
		"$(readlink -f "${argv0}")" < "${sfeedtmpdir}/jobs"
	statuscode=$?

	# check error exit status indicator for parallel jobs.
	[ -f "${sfeedtmpdir}/ok" ] || statuscode=1
	# on signal SIGINT and SIGTERM exit with signal number + 128.
	[ ${signo} -ne 0 ] && die $((signo+128))
	die ${statuscode}
}

# process a single feed.
# parameters are: config, tmpdir, name, feedurl, basesiteurl, encoding
if [ "${SFEED_UPDATE_CHILD}" = "1" ]; then
	IFS="" # "\037"
	[ "$1" = "" ] && exit 0 # must have an argument set
	printf '%s\n' "$1" | \
	while read -r _config _tmpdir _name _feedurl _basesiteurl _encoding; do
		# load config file, sets $config.
		loadconfig "${_config}"
		sfeedtmpdir="${_tmpdir}"
		_feed "${_name}" "${_feedurl}" "${_basesiteurl}" "${_encoding}"
		exit "$?"
	done
	exit 0
fi

# ...else parent mode:
argv0="$0" # remember $0, in shells like zsh $0 is the function name.
[ "${SFEED_UPDATE_INCLUDE}" = "1" ] || main "$@"