#!/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="${1}"
	local new_sessions="${2}"
	shift 2
	local ret=
	local service_script=

	ret=0
	for service_script in "${XDG_CONFIG_HOME:-${HOME}/.config}/homerc/"*; do
		"$(dirname "${0}")/svc" "${service_script##*/}" \
			"${old_sessions};${new_sessions}" || ret=1
	done

	return ${ret}
}

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 1
	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
		# No running sessions of specified 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 1
	fi

	return 0
}

list_sessions()
{
	local printed=
	local session=
	local s_type=

	printed=false
	IFS=','
	for session in ${sessions}; do
		unset IFS
		case "${session}" in '') continue;; esac
		s_type="$(printf '%s' "${session}" | tr ':' '_')"
		if ${printed}; then
			printf ', '
		fi
		eval "printf '%s (%d)' \"\${session}\" \${sessions_${s_type}}"
		printed=true
	done
	unset IFS

	return 0
}

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

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

	return 0
}

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

	cachedir="${XDG_CACHE_HOME:-${HOME}/.cache}/homerc"
	mkdir -p "${cachedir}/run"

	exec 0<&-
	exec 1>>"${cachedir}/rc.log" 2>&1
	trap '' HUP

	beg_session "${session_type}"
	listen

	rm "${rc_fifo}"

	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 0<"${res_fifo}" && \
				[ "x${magic}" = "x${MAGIC}" ]; then
			info 'Sessions: %s' "${list}"
			rm "${res_fifo}"
		else
			error 'Failed to communicate with running daemon'
			rm "${res_fifo}"
			return 1
		fi
	fi

	return 0
}

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

	return 0
}

usage()
{
	printf 'Usage: %s {start|stop} <session-type>\n' "${0}"
	printf '   or: %s {status|quit}\n\n' "${0}"
	printf '<session-type> is one or more strings of alphanumeric '
	printf 'characters\nseparated by colons.\n'

	return 0
}

main()
{
	local action="${1-}"
	local session_type="${2-}"

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

	case "${action}" in
		'start' | 'stop')
			if [ ${#} -ne 2 ] || ! valid_session_type \
					"${session_type}"; then
				usage 1>&2
				return 1
			fi
			"${action}" "${session_type}"
			;;
		'status')
			if [ ${#} -ne 1 ]; then
				usage 1>&2
				return 1
			fi
			status
			;;
		'quit')
			if [ ${#} -ne 1 ]; then
				usage 1>&2
				return 1
			fi
			quit
			;;
		*)
			usage 1>&2
			return 1
			;;
	esac

	return 0
}

main "${@}"