#!/bin/sh -e
#
# 2016 Daniel Heule (hda at sfs.biz)
# Copyright 2017, Philippe Gregoire <pg@pgregoire.xyz>
# 2020 Dennis Camera (dennis.camera at ssrq-sds-fds.ch)
#
# This file is part of cdist.
#
# cdist is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# cdist is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with cdist. If not, see <http://www.gnu.org/licenses/>.
#
#
# Returns the name of the init system (PID 1)
#
# Expected values:
# Linux:
#  Adélie Linux:
#    sysvinit+openrc
#  Alpine Linux:
#    busybox-init+openrc
#  ArchLinux:
#    systemd, sysvinit
#  CRUX:
#    sysvinit
#  Debian:
#    systemd, upstart, sysvinit, openrc, ???
#  Devuan:
#    sysvinit, ???
#  Gentoo:
#    sysvinit+openrc, openrc-init, systemd
#  OpenBMC:
#    systemd
#  OpenWrt:
#    procd, init??
#  RedHat (RHEL, CentOS, Fedora, RedHat Linux, ...):
#    systemd, upstart, sysvinit
#  Slackware:
#    sysvinit
#  SuSE:
#    systemd, sysvinit
#  Ubuntu:
#    systemd, upstart, sysvinit
#
# GNU:
#   Debian:
#     hurd-init, sysvinit
#
# BSD:
#  {Free,Open,Net}BSD:
#    init
#
# Mac OS X:
#   launchd, init
#
# Solaris/Illumos:
#   smf, init


# [root@fedora-12 ~]# readlink /proc/1/exe
# /sbin/init (deleted)
# [root@fedora-12 ~]# ls -l /proc/1/exe
# lrwxrwxrwx. 1 root root 0 2020-01-30 23:00 /proc/1/exe -> /sbin/init (deleted)

set -e
#set -x  # DEBUG

validate_busybox_init() {
	# It is quite common to use SysVinit to stack other init systemd
	# (like OpenRC) on top of it. So we check for that, too.
	if stacked=$(validate_openrc)
	then
		echo "busybox-init+${stacked}"
	else
		echo busybox-init
	fi
}

validate_hurd_init() {
	# FIXME: Test me!
	test -x /hurd/init || return 1
	grep -q 'GNU Hurd' /hurd/init || return 1
	echo hurd-init
}

validate_openrc() {
	test -f /run/openrc/softlevel || return 1
	echo openrc
}

validate_procd() {
	grep -q 'procd' /sbin/procd || return 1
	echo procd
}

validate_runit() {
	test -d /run/runit || return 1
	echo runit
}

validate_smf() {
	# XXX: Is this the correct way??
	test -f /etc/svc/volatile/svc_nonpersist.db || return 1
	echo smf
}

validate_systemd() {
	# NOTE: sd_booted(3)
	test -d /run/systemd/system/ || return 1
	# systemctl --version | sed -e '/^systemd/!d;s/^systemd //'
	echo systemd
}

validate_sysvinit() {
	test -x /sbin/init \
	 && grep -q 'INIT_VERSION=sysvinit-[0-9.]*' /sbin/init \
	 || return 1

	# It is quite common to use SysVinit to stack other init systemd
	# (like OpenRC) on top of it. So we check for that, too.
	if stacked=$(validate_openrc)
	then
		echo "sysvinit+${stacked}"
	else
		echo sysvinit
	fi
	unset stacked
}

validate_upstart() {
	test -x "$(command -v initctl)" || return 1
	case $(initctl version)
	in
		*'(upstart '*')')
			# if type -d /etc/init
			# then
			# 	# modern (DBus-based?) upstart >= 0.5
			# 	:
			# elif type -d /etc/events.d
			# then
			# 	# ancient upstart
			# 	:
			# fi
			echo upstart
			;;
		*)
			return 1
			;;
	esac
}

find_init_procfs() (
	# First, check if the required file in procfs exists...
	test -h /proc/1/exe || return 1

	# Find init executable
	init_exe=$(ls -l /proc/1/exe 2>/dev/null)
	init_exe=${init_exe#* -> }

	if ! test -x "$init_exe"
	then
		# On some rare occasions it can happen that the
		# running init's binary has been replaced. In this
		# case Linux adjusts the symlink to "X (deleted)"
		case $init_exe
		in
			*' (deleted)')
				init_exe=${init_exe% (deleted)}
				test -x "$init_exe" || exit 1
				;;
			*)
				exit 1
				;;
		esac
	fi

	echo "${init_exe}"
)

# BusyBox's versions of ps and pgrep do not support some options
# depending on which compile-time options have been used.

find_init_pgrep() {
	pgrep -P0 -fl 2>/dev/null | awk -F '[[:blank:]]' '$1 == 1 { print $2 }'
}

find_init_ps() {
	case $(uname -s)
	in
		Darwin|NetBSD)
			ps -o ucomm= -p 1 2>/dev/null
			;;
		FreeBSD)
			ps -o command= -p 1 2>/dev/null | cut -d ' ' -f 1
			;;
		OpenBSD)
			ps -o command -p 1 2>/dev/null | tail -n +2 | cut -d ' ' -f 1
			;;
		*)
			ps -o comm= -p 1 2>/dev/null
			;;
	esac
}

find_init() {
	case $(uname -s)
	in
		Linux|GNU|NetBSD)
			find_init_procfs || find_init_pgrep || find_init_ps
			;;
		FreeBSD)
			find_init_procfs || find_init_ps
			;;
		OpenBSD)
			find_init_pgrep || find_init_ps
			;;
		Darwin|FreeBSD|SunOS)
			find_init_ps
			;;
		*)
			echo "Don't know how to determine init." >&2
			echo 'Please send a patch.' >&2
			exit 1
	esac
}

validate_by_comm_name() {
	case $1
	in
		busybox)
			validate_busybox_init
			;;
		init)
			# FIXME: Do some more magic here!
			echo init
			;;
		openrc-init)
			validate_openrc >/dev/null && echo openrc-init
			;;
		runit)
			validate_runit
			;;
		systemd)
			validate_systemd
			;;
		*)
			# Run validate function by comm name if available.
			# Fall back to comm name if either it does not exist or
			# returns non-zero.
			type "validate_$1" >/dev/null && "validate_$1" || echo $1
	esac
}

try_all() {
	# init: it could be anything...
	# We try some approaches to gather more information about init without
	# calling it! On some init systemd this triggers a reinitialisation of
	# the system which we don't want (e.g. embedded systems).

	validate_sysvinit || \
	validate_openrc || \
	validate_runit || \
	validate_smf || \
	validate_upstart || \
	validate_hurd_init || \
	echo init  # fallback
}

init=$(find_init)

if test -x "${init}"
then
	case $init
	in
		/hurd/init)
			# FIXME: Create validate function
			echo hurd-init
			;;
		*/init)
			try_all
			;;
		*)
			validate_by_comm_name "$(basename "${init}")"
			;;
	esac
else
	validate_by_comm_name "${init}"
fi