#!/bin/sh

set -eu

RC_MAGIC='~/rc'

progname=
rc_fifo=

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

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

	return 0
}

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

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

# Returns 0 if the session is the first of its type or was last of its type
# TODO: Handle decrement from 0.
inc_session()
{
	local s_type="${1}"
	local dir=${2}
	shift 2
	local ret=

	ret=1

	s_type="$(printf '%s' "${s_type}" | tr ':' '_')"
	eval "[ \${sessions_${s_type}:-0} -eq 0 ] && ret=0"
	eval "sessions_${s_type}=\$((\${sessions_${s_type}:-0} + ${dir}))"
	eval "[ \${sessions_${s_type}} -eq 0 ] && ret=0"

	return ${ret}
}

chg_session()
{
	local session_type="${1}"
	local inc_dir=${2}
	local diff="${3}"
	shift 3

	while :; do
		case "${session_type}" in *:*);; *) break;; esac
		if inc_session "${session_type}" ${inc_dir}; then
			diff="${diff}${session_type},"
		fi
		session_type="${session_type%:*}"
	done

	diff="${diff%,}"
}

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

	chg_session "${session_type}" 1 '+'
	return ${?}
}

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

	chg_session "${session_type}" -1 '-'
	return ${?}
}

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

	while :; do
		if read -r magic cmd arg; then
			case "${magic}" in "${RC_MAGIC}");; *)
				continue
			esac
		fi
		case "${cmd}" in
			'beg')
				if valid_session_type "${arg}"; then
					beg_session "${arg}"
				fi
				;;
			'end')
				if valid_session_type "${arg}"; then
					end_session "${arg}"
				fi
				;;
			'bye')
				break
				;;
			*)
				continue
				;;
		esac
	done 0<"${rc_fifo}"
}

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

	if mkfifo "${rc_fifo}" 2>/dev/null; then
		beg_session "${session_type}"
		listen
		rm "${rc_fifo}"
	else
		# Signal the running rc daemon.
		printf "%s beg %s\n" "${RC_MAGIC}" "${session_type}" \
			1>"${rc_fifo}"
	fi

	return 0
}

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

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

	return 0
}

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

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

	return 0
}

main "${@}"