#!/bin/bash
set -euo pipefail

api_host="https://api.digitalocean.com/v2"
sleep_interval=${SLEEP_INTERVAL:-300}
remove_duplicates=${REMOVE_DUPLICATES:-"false"}

# Only services with ipv6 supported are listed here.
# And are not using cloudflare or similar services
# that may block requests from this script.
services=(
    "ifconfig.io"
)

die() {
    echo "$1"
    exit 1
}

test -f "${DIGITALOCEAN_TOKEN_FILE:-}" && DIGITALOCEAN_TOKEN="$(cat $DIGITALOCEAN_TOKEN_FILE)"
test -z $DIGITALOCEAN_TOKEN && die "DIGITALOCEAN_TOKEN not set!"
test -z $DOMAIN && die "DOMAIN not set!"
test -z $NAME && die "NAME not set!"

dns_list="$api_host/domains/$DOMAIN/records"

configure_record() {
  # disable glob expansion
  set -f

  ip=$1
  type=$2

  for sub in ${NAME//;/ }; do
    record_id=$(echo $domain_records| jq ".domain_records[] | select(.type == \"$type\" and .name == \"$sub\") | .id")
    record_data=$(echo $domain_records| jq -r ".domain_records[] | select(.type == \"$type\" and .name == \"$sub\") | .data")

    if [ $(echo "$record_id" | wc -l) -ge 2 ]; then :
      if [[ "${remove_duplicates}" == "true" ]]; then :
        echo "'$sub' domain name has duplicate DNS records, removing duplicates"
        record_id_to_delete=$(echo "$record_id"| tail -n +2)
        record_id=$(echo "$record_id"| head -1)
        record_data=$(echo "$record_data"| head -1)

        while IFS= read -r line; do
          curl -s -X DELETE \
            -H "Content-Type: application/json" \
            -H "Authorization: Bearer $DIGITALOCEAN_TOKEN" \
            "$dns_list/$line" &> /dev/null
        done <<< "$record_id_to_delete"
      else :
        echo "Unable to update '$sub' domain name as it has duplicate DNS records. Set REMOVE_DUPLICATES='true' to remove them."
        continue
      fi
    fi

  # re-enable glob expansion
  set +f

  data="{\"type\": \"$type\", \"name\": \"$sub\", \"data\": \"$ip\"}"
  url="$dns_list/$record_id"

  if [[ -z $record_id ]]; then
    echo "No record found with '$sub' domain name. Creating record, sending data=$data to url=$url"

    new_record=$(curl -s -X POST \
      -H "Content-Type: application/json" \
      -H "Authorization: Bearer $DIGITALOCEAN_TOKEN" \
      -d "$data" \
      "$url")

    record_data=$(echo $new_record| jq -r ".data")
  fi

  if [[ "$ip" != "$record_data" ]]; then
    echo "existing DNS record address ($record_data) doesn't match current IP ($ip), sending data=$data to url=$url"

    curl -s -X PUT \
      -H "Content-Type: application/json" \
      -H "Authorization: Bearer $DIGITALOCEAN_TOKEN" \
      -d "$data" \
      "$url" &> /dev/null
    else
      echo "existing DNS record address ($record_data) did not need updating"
    fi
  done
}

while ( true )
do
    domain_records=$(curl -s -X GET \
        -H "Content-Type: application/json" \
        -H "Authorization: Bearer $DIGITALOCEAN_TOKEN" \
        $dns_list"?per_page=200")

    for service in ${services[@]}
    do
        echo "Trying with $service..."

        ipv4="$(curl -4 -s -f --connect-timeout=2 $service || echo "")"
        ipv6="$(curl -6 -s -f --connect-timeout=2 $service || echo "")"

        if [[ -n "$ipv4$ipv6" ]]
        then
            break
        else
            echo "Failed to retrieve IP from $service"
        fi
    done

    if [[ -z $ipv4 ]]
    then
        echo "IPv4 wasn't retrieved within allowed interval. Will try $sleep_interval seconds later.."
    else
      echo "Found IPv4 address $ipv4"
      configure_record $ipv4 "A"
    fi

    if [[ -z $ipv6 ]]
    then
        echo "IPv6 wasn't retrieved within allowed interval. Will try $sleep_interval seconds later.."
    else
      echo "Found IPv6 address $ipv6"
      configure_record $ipv6 "AAAA"
    fi 

    sleep $sleep_interval
done