#!/bin/sh
# vi: ts=4 noexpandtab syntax=sh

ETC_CONFIG=/etc/ec2-init/is-compat-env
CONFIG_ACTIVE_VAR="compat"
CMDLINE_EC2_COMPAT=ec2init
CR="
"
VERBOSE=1
META_DATA_URL=http://169.254.169.254/2009-04-04
check_md=0

Usage() {
	cat <<EOF
Usage: ${0##*/} [options]
   indicate whether or not this appears to be an ec2 environment
   a exit value:
     0 indicates this is ec2
     1 indicates this is not ec2

options:
	-h | --help       display usage
	-m | --meta-data  check metadata service
	-q | --quiet      do not output 'yes' or 'no', only exit properly
EOF
}

xit() {
	ret=${1:-1}
	if [ "${VERBOSE}" != "0" ]; then
		[ "$ret" = "0" ] && echo yes || echo no
	fi
	exit "$ret";
}

while [ $# -ne 0 ]; do
	case "$1" in
		-q|--quiet) VERBOSE=0;;
		-h|--help) Usage; exit 0;;
		-m|--use-meta-data) check_md=1;;
		*) Usage 1>&2; exit 2;;
	esac
	shift;
done

if [ ${check_md} -ne 0 ]; then
	# if we are to check for meta data service
	# then check first that there was something there.
	index=$(wget --connect-timeout=2 --tries 2 -O - -q "${META_DATA_URL}") ||
		xit 1

	# exit true if content of url a line with 'meta-data' at start
	[ "${index#*${CR}meta-data}" = "${index}" ] || xit 0
	xit 1
fi

# if /proc/cmdline exists and has certain tokens, trust them
# even before looking at config file
if [ -e /proc/cmdline ] && read cmdline < /proc/cmdline; then
	# if cmdline has certain tokens in it, trust them
	case " ${cmdline} " in
		*\ ${CMDLINE_EC2_COMPAT}=1\ *) xit 0;;
		*\ ${CMDLINE_EC2_COMPAT}=0\ *) xit 1;;
	esac
fi

# if the config file exists and has a non-empty value set for
# CONFIG_ACTIVE_VAR trust it as definitive source. If no value is set
# fall through
if [ -e "${ETC_CONFIG}" ] &&
    active=$(sh -c "unset ${CONFIG_ACTIVE_VAR};
             . '${ETC_CONFIG}'; echo \${${CONFIG_ACTIVE_VAR}}") && 
    [ -n "${active}" ]; then
    [ "$active" = "1" ] && xit 0
    xit 1
fi

xit 1