#!/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 process name of pid 1 ( normaly the init system )
# for example at linux this value is "init" or "systemd" in most cases
#

set -e

# Expected values:
# Linux:
#  Gentoo:
#	 sysvinit, openrc-init

# GNU:
#	Debian:
#	  hurd-init, sysvinit

# [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)

# inspired by https://stackoverflow.com/a/33266819
shreadlink() (
	CDPATH=
	target=$1 fname= targetDir=

	# Resolve potential symlinks until the ultimate target is found.
	while :
	do
		if ! test -e "$target"
		then
			printf 'ERROR: %s does not exist.\n' "'$target'" >&2
			return 1
		fi

		# Change to target dir; necessary for correct resolution of target path.
		cd "$(dirname -- "$target")"

		fname=$(basename -- "$target") # Extract filename.
		[ "$fname" = '/' ] && fname='' # !! curiously, `basename /` returns '/'

		[ -L "$fname" ] || break

		# Extract [next] target path, which may be defined
		# *relative* to the symlink's own directory.
		# Note: We parse `ls -l` output to find the symlink target
		#		which is the only POSIX-compliant, albeit somewhat fragile, way.
		# FIXME: Will break if one of the filenames contain ’ -> ’
		target=$(ls -l "$fname" | sed -e 's/^.* -> //')
	done

	# Get canonical dir. path
	targetDir=$(pwd -P)

	# Output the ultimate target's canonical path.
	# Note that we manually resolve paths ending in /. and /.. to make sure we have a normalized path.
	if test "$fname" = '.'
	then
		printf '%s\n' "${targetDir%/}"
	elif test "$fname" = '..'
	then
		# Caveat: something like /var/.. will resolve to /private (assuming /var@ -> /private/var), i.e. the '..' is applied
		# AFTER canonicalization.
		printf '%s\n' "$(dirname -- "${targetDir}")"
	else
		printf '%s/%s\n' "${targetDir%/}" "$fname"
	fi
)


case $(uname -s) in
	Linux|GNU)
		# if test -f /proc/1/comm
		# then
		#	  comm_name=$(cat /proc/1/comm)
		# else
			# BusyBox's versions of ps and pgrep do not support some options
			# depending on which compile-time options have been used.
			# Both pgrep and ps are tried to get the command name
		#	  comm_name=$(
		#		  pgrep -P0 -l 2>/dev/null | awk '/^1[ \t]/ { print $2 }'
		#		  || ps -o comm= -p 1 2>/dev/null)
		# fi

		init_exe=$(shreadlink /proc/1/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

		if test "$init_exe" = '/hurd/init'
		then
			# XXX: Could maybe be removed
			echo hurd-init
			exit 0
		fi

		comm_name=$(basename "$init_exe")
		case $comm_name
		in
			init)
				:  # handled below
				;;
			systemd)
				# NOTE: sd_booted(3)
				if test -d /run/systemd/system/
				then
					echo systemd
					exit 0
				fi
				# otherwise: treat like "init"
				;;
			*)
				echo "$comm_name"
				exit 0
				;;
		esac

		# init: it could be anything...
		case $("$init_exe" --version 2>/dev/null | head -n 1)
		in
			SysV*)
				# This is a little bit more specific than init
				echo sysvinit
				exit 0
				;;
			*'GNU Hurd'*)
				echo hurd-init
				;;
			*upstart*)
				echo upstart
				exit 0
				;;
		esac
		case $("$init_exe" --help 2>/dev/null | head -n 1)
		in
			BusyBox*)
				echo busybox
				exit 0
				;;
		esac

		echo init
		;;
	FreeBSD|OpenBSD)
		ps -o comm= -p 1 2>/dev/null || true
		;;
	Darwin)
		basename "$(ps -o comm= -p 1 2>/dev/null)"
		;;
	SunOS)
		comm_name=$(ps -o comm= -p 1 2>/dev/null)
		if test "$(basename "$comm_name")" != 'init'
		then
			echo "${comm_name}"
			exit 0
		fi

		# XXX: Is this the correct way??
		if test -f /etc/svc/volatile/svc_nonpersist.db
		then
			echo smf
			exit 0
		fi
		;;
	*)
		# return a empty string as unknown value
		echo ""
		;;
esac