#!/bin/sh

set -eu

MAGIC='~/rc'

progname=
rc_fifo=
res_fifo=
sessions=','

info()
{
	local fmt="${1}"
	shift 1

	printf "%s: ${fmt}\n" "${progname}" "${@}"

	return 0
}

error()
{
	local fmt="${1}"
	shift 1

	printf "%s: Error: ${fmt}\n" "${progname}" "${@}" 1>&2

	return 0
}

valid_session_type()
{
	local session_type="${1}"
	shift 1

	case "${session_type}" in *[!A-Za-z0-9:]* | '' | ':'* | *':')
		return 1
	esac
	return 0
}

run_services()
{
	local old_sessions="${1}"
	local new_sessions="${1}"
	shift 1
	local service_script=

	for service_script in "${XDG_CACHE_HOME:-${HOME}/.cache}/homerc/"*; do
		"$(dirname ${0})/svc" "${service_script##*/}" \
			"${old_sessions};${new_sessions}"
	done
}

beg_session()
{
	local session_type="${1}"
	shift 1
	local s_type=
	local add=
	local new_sessions=
	local old_sessions=

	s_type="$(printf '%s' "${session_type}" | tr ':' '_')"

	if eval "[ \${sessions_${s_type}:-0} -eq 0 ]"; then
		add=true
	else
		add=false
	fi

	# Increment.
	eval "sessions_${s_type}=\$((\${sessions_${s_type}:-0} + 1))"

	if ${add}; then
		new_sessions="${sessions}${session_type},"
		old_sessions="${sessions}"
		sessions="${new_sessions}"
		run_services "${old_sessions}" "${new_sessions}"
		return ${?}
	fi

	return 0
}

end_session()
{
	local session_type="${1}"
	shift 1
	local s_type=
	local new_sessions=
	local old_sessions=

	s_type="$(printf '%s' "${session_type}" | tr ':' '_')"

	if eval "[ \${sessions_${s_type}:-0} -eq 0 ]"; then
		error 'No running sessions of type %s' "${session_type}"
		return 1
	fi

	# Decrement.
	eval "sessions_${s_type}=\$((\${sessions_${s_type}} - 1))"

	if eval "[ \${sessions_${s_type}} -eq 0 ]"; then
		eval "unset sessions_${s_type}"
		new_sessions="${sessions%,${session_type},*}"
		new_sessions="${new_sessions},${sessions#*,${session_type},}"
		old_sessions="${sessions}"
		sessions="${new_sessions}"
		run_services "${old_sessions}" "${new_sessions}"
		return ${?}
	fi

	return 0
}

list_sessions()
{
	local printed=
	local session=

	printed=false
	IFS=','
	for session in ${sessions}; do
		unset IFS
		if ${printed}; then
			printf ', '
		fi
		eval "printf '%s (%d)' '${session}' \${sessions_${session}}"
		printed=true
	done
	unset IFS
}

listen()
{
	local magic=
	local cmd=
	local arg=

	while :; do
		if read -r magic cmd arg; then
			case "${magic}" in "${MAGIC}");; *)
				continue
			esac
			case "${cmd}" in
				'beg')
					if valid_session_type "${arg}"; then
						beg_session "${arg}"
					fi
					;;
				'end')
					if valid_session_type "${arg}"; then
						end_session "${arg}"
					fi
					;;
				'who')
					{
						printf '%s ' "${MAGIC}"
						list_sessions
						printf '\n'
					} 1>"${arg}"
					;;
				'bye')
					break
					;;
				*)
					continue
					;;
			esac
		fi
	done 0<"${rc_fifo}"
}

run_daemon()
{
	local session_type="${1}"
	shift 1
	local piddir=

	exec 0<&- 1>&- 2>&-
	# TODO:
	# Disassociate from its process group (usually a shell), to insulate
	# itself from signals (such as HUP) sent to the process group
	# Ignore all terminal I/O signals

	piddir="${XDG_CACHE_HOME:-${HOME}/.cache}/homerc"
	mkdir -p "${piddir}"
	rm -f "${piddir}/"*

	beg_session "${session_type}"
	listen
	rm "${rc_fifo}"
	rm -f "${piddir}/"*

	return 0
}

start()
{
	local session_type="${1}"
	shift 1

	if mkfifo -m 0600 "${rc_fifo}" 2>/dev/null; then
		run_daemon "${session_type}" &
	else
		# Signal the running rc daemon.
		printf "%s beg %s\n" "${MAGIC}" "${session_type}" \
			1>"${rc_fifo}"
	fi

	return 0
}

stop()
{
	local session_type="${1}"
	shift 1

	if mkfifo -m 0600 "${rc_fifo}" 2>/dev/null; then
		# Daemonizing just to end a non-existent session makes no sense.
		error 'No running daemon found'
		rm "${rc_fifo}"
		return 1
	else
		# Signal the running rc daemon.
		printf "%s end %s\n" "${MAGIC}" "${session_type}" \
			1>"${rc_fifo}"
	fi

	return 0
}

status()
{
	local magic=
	local list=

	if mkfifo -m 0600 "${rc_fifo}" 2>/dev/null; then
		# Daemonizing just to list non-existent sessions makes no sense.
		error 'No running daemon found'
		rm "${rc_fifo}"
		return 1
	else
		# Establish response FIFO.
		if ! mkfifo -m 0600 "${res_fifo}" 2>/dev/null; then
			error 'Failed to communicate with running daemon'
			return 1
		fi
		# Signal the running rc daemon.
		printf "%s who %s\n" "${MAGIC}" "${res_fifo}" \
			1>"${rc_fifo}"
		if read -r magic list; then
			case "${magic}" in "${MAGIC}");; *)
				continue
			esac
			info 'Sessions: %s' "${list}"
		else
			error 'Failed to communicate with running daemon'
			rm "${res_fifo}"
			return 1
		fi
	fi

	return 0
}

usage()
{
	printf 'Usage: %s {start|stop} <session-type>\n' "${0}"
	printf '   or: %s status\n' "${0}"

	return 0
}

main()
{
	local action=
	local session_type=

	if [ ${#} -ne 2 ]; then
		usage 1>&2
		return 1
	fi
	action="${1}"
	session_type="${2}"

	if ! valid_session_type; then
		error 'Invalid session type'
		return 1
	fi

	progname="${0##*/}"
	rc_fifo="/tmp/homercrc-$(id -u)"
	res_fifo="/tmp/homercres-${$}"

	case "${action}" in
		'start')
			start "${session_type}"
			;;
		'stop')
			stop "${session_type}"
			;;
		'status')
			status
			;;
		*)
			usage 1>&2
			return 1
			;;
	esac

	return 0
}

main "${@}"