#!/bin/execlineb
#
# This is the turnstile s6-rc backend. It accepts the action as its first
# argument, which is either "ready", "run", or "stop". The backend can be
# written in any language, in this case the shebang is used to run it.
#
# It also serves as an example of how to implement such backend in a non
# shell language.
#
# Arguments for "ready":
#
# live:     the path to s6-rc's live dir; it is the string that is
#           written by dinit into ready_fd for the "run" part of the process
#
# Arguments for "run":
#
# ready_p:  path to named pipe (fifo) that should be poked with a string; this
#           will be passed to the "ready" script of the sequence as its sole
#           argument (here this is the path to s6-rc's live state directory)
# srvdir:   an internal directory that can be used by the service manager
#           for any purpose (usually to keep track of its state)
# confdir:  the path where turnstile's configuration data reside, used
#           to source the configuration file
#
# Arguments for "stop":
#
# pid:      the PID of the service manager to stop (gracefully); it should
#           terminate the services it's running and then stop itself
#
# How the script manages its configuration and so on is up to the script.
#
# Note that the script *must* exec the service manager directly, i.e. the
# service manager must fully replace the shell process for this to work.
#
# Copyright 2024 Carlos Eduardo <carana2099@gmail.com>
# License: BSD-2-Clause
#

importas -i directive 1
shift -n 1

case $directive {
	run {
		# source additional arguments.
		# two subsitution steps are needed because https://skarnet.org/lists/skaware/2049.html
		multisubstitute {
			importas -i __confdir 3
			importas -i __home    HOME
		}
		envfile -I -- ${__confdir}/s6-rc.conf

		# despite the above warning, we do want serial substitution on these, so we import it here, before the bigger multisubstitute.
		multisubstitute {
			importas -uD "${HOME}/.local/share/s6" compiled compileddir
			importas -uD "${statedir}/s6-rc"       live     livestatedir
			importas -uD "${statedir}/env"         env      envdir
		}
		multisubstitute {
			importas -i readyfifo 1
			importas -i statedir 2
			importas -i confdir 3
			# not used directly, but might be useful for the config file
			importas -Si HOME
			importas -Si USER
			importas -Si XDG_RUNTIME_DIR
			importas -Si SHELL
			importas -Si LOGNAME
		}

		# Initialize state directory.
		# confdir/s6 should have the definition for a s6-svscan-log
		# service that acts as the catch-all loger. See:
		# /run/service/s6-svscan-log
		# on a s6-linux-init powered machine for an example.
		# It should also contain a .s6-svscan/SIGINT file with
		# foreground { s6-rc -bDa } s6-svscanctl -t .
		if { cp -a -- ${confdir}/s6 ${statedir}/service }

		pipeline -dw -- {
			if {
				forstdin -x0 _
					exit 0
			}
			if -nt {
				# Create envdir.
				if { mkdir -p -- ${env} }
				# Init service management layer.
				if { s6-rc-init -c $compiled -l $live -- ${statedir}/service }
				# Wait for logger to come up.
				redirfd -w 2 ${statedir}/service/s6-svscan-log/fifo
				# Print string for the ready step.
				redirfd -w 1 ${readyfifo}
				printf %s $live
			}
			# tell s6-svscan to give up if anything goes awry.
			s6-svscanctl -t -- ${statedir}/service
		}
			# turn pipeline output into notification-fd.
			fdmove -c 3 1
			# backup stderr for catch-all logger
			fdmove -c 4 2
			# fifo trick
			redirfd -wnb 2 ${statedir}/service/s6-svscan-log/fifo
			fdmove -c 1 2
			# avoid leaking script arguments
			emptyenv -P
			# export extra info for helper scripts
			export SVDIR ${statedir}/service
			export TURNSTILE_S6RC_LIVESTATE_DIR ${live}
			s6-svscan -d 3 -X 4 -- ${statedir}/service
	}
	ready {
		importas -i string 1
		s6-rc -l $string -up change default
	}
	stop {
		importas -i ! 1
		# Using INT instead of TERM so the s6-rc -bDa change hook runs
		kill -s INT $!
	}
}
	exit 32