#!/usr/bin/bash

source /etc/sysconfig/chronyd

set -u -o pipefail -o nounset
shopt -s nullglob

rundir="/run/chrony.d"

declare -i installed_new_sources=0

reload_sources() {
        local code=$?
        if [ $installed_new_sources -gt 0 ]; then
                # reload sources if chronyd is running. We may be
                # started before chronyd, so don't log an error if
                # it's not yet running
                chronyc reload sources > /dev/null 2>&1 || true
        fi
        exit $code
}

trap reload_sources EXIT

main () {

	[ -d "$rundir" ] || install -Z -o root -g root -m0755 -d "$rundir"
	static_sources=(/etc/chrony.d/*.sources "${rundir}"/*.sources)
	for f in "${static_sources[@]}"; do
		# If there are existing sources, we have no thing to do
		[ ! -L "$f" ] && [ -s "$f" ] && exit 0
	done

        local dhcp_sources_installed
        dhcp_sources
        dhcp_sources_installed=$?

        case $dhcp_sources_installed in
            0)
                # we've installed new sources
                exit 0
                ;;
            1)
                # DHCP leases contain no time sources at all
                :
                ;;
            2)
                # Time sources are unchanged from the previous run
                exit 0
                ;;
        esac

	if [[ $USE_AMAZON_NTP_POOL == 'no' || $USE_AMAZON_NTP_POOL == 'false' ]]; then
		# We'll use the public NTP pools only. These time sources
		# present standard leap-second handling, so we disable the
		# Amazon-provided smearing sources per
		# https://www.rfc-editor.org/rfc/rfc8633.html#section-3.7.1
		rm_sources
		public_pool
	elif [[ $USE_AMAZON_NTP_POOL == 'yes' || $USE_AMAZON_NTP_POOL == 'true' ]]; then
		# Ensures that Amazon NTP endpoints are refreshed in the case this instance
		# has been launched in another partition or switched between IPv4 & IPv6.
		rm_sources
		link_local
		amazon_pool
	fi
}

rm_sources() {
	rm -f "${rundir}"/*.sources
}

ln_sources() {
	local basename partition cfg p

	basename="$1"
	partition="${2:-unspecified}"
	for p in "$partition" aws; do
		cfg="/usr/share/amazon-chrony-config/${basename}_${p}.sources"
		if [ -f "$cfg" ]; then
                        installed_new_sources+=1
			ln -s "$cfg" "${rundir}/${basename}.sources"
			return
		fi
	done
	echo "WARNING: No ${basename} sources for partition $partition" >&2
}

# Configure time sources received via DHCP leases in $rundir/dhcp.sources
# Return values:
#  0: We have installed a new list of time sources from DHCP
#  1: The DHCP lease does not contain any time sources
#  2: The DHCP lease contains time sources that are unchanged from a prior run
dhcp_sources () {
        local servers
        local cfg="${rundir}/dhcp.sources"
        servers=$(
            busctl call -j org.freedesktop.network1 \
                   /org/freedesktop/network1 \
                   org.freedesktop.network1.Manager \
                   Describe \
                | jq -r '.data[0]' \
                | jq '.Interfaces[].NTP[]?.Address | join(".") as $foo | "server " + $foo + " prefer iburst minpoll 4 maxpoll 4"' -r
               )
        if [ -n "$servers" ]; then
                if [ -f "$cfg" ]; then
                        local old_md5 new_md5
                        old_md5=$(md5sum "$cfg" | awk '{print $1}')
                        new_md5=$(echo "$servers" | md5sum | awk '{print $1}')
                        if [ "$old_md5" = "$new_md5" ]; then
                                # server list is unchanged
                                return 2
                        fi
                fi
                # The DHCP-provided sources should be the only ones we use, remove any others
                rm_sources
                echo "$servers" > "$rundir/.dhcp.sources"
                mv "$rundir/.dhcp.sources" "$cfg"
                installed_new_sources+=1
                return 0
        fi

        if [ -f "$cfg" ]; then
                # clean up any stale sources from older DHCP leases
                # and ensure we reload to reflect the removal
                rm -f "$cfg"
                installed_new_sources+=1
        fi
                
        return 1
}

# Install a partition-appropriate Amazon network time endpoint,
# defaulting to the classic "aws" partition
amazon_pool () {
	local partition cfg
	partition=$(ec2-metadata --quiet --partition)
	if [ $? -eq 0 ]; then
		ln_sources amazon-pool "$partition"
		return 0
	fi
	echo "ec2-metadata returned nonzero" >&2
}

# Install one, but not both, of the link-local time sources
link_local () {
	local v6_endpoint=fd00:ec2::123
	if ip -6 ro get $v6_endpoint > /dev/null 2>&1; then
		ln_sources link-local-ipv6
		return
        fi
	ln_sources link-local-ipv4
}

public_pool () {
	ln -s /usr/share/chrony/ntp-pool.sources "$rundir"
        installed_new_sources+=1
}

main "$@"