#!/usr/bin/env bash
set -euo pipefail

# Print the current public IPv4 address, with fast fallbacks.

endpoints=(
  "https://ipv4.icanhazip.com"
  "https://ipinfo.io/ip"
  "https://ifconfig.co/ip"
  "https://api.ipify.org"
  "https://checkip.amazonaws.com"
)

curl_opts=( -4 -fsS --max-time 2 --retry 0 )

validate_ipv4() {
  local ip="$1"
  [[ "$ip" =~ ^([0-9]{1,3}\.){3}[0-9]{1,3}$ ]] || return 1
  IFS=. read -r a b c d <<< "$ip" || return 1
  for o in "$a" "$b" "$c" "$d"; do
    [[ "$o" -ge 0 && "$o" -le 255 ]] || return 1
  done
  printf '%s\n' "$ip"
}

for url in "${endpoints[@]}"; do
  if out=$(curl "${curl_opts[@]}" "$url" 2>/dev/null | tr -d ' \t\n\r'); then
    ip=$(printf '%s' "$out" | grep -Eo '([0-9]{1,3}\.){3}[0-9]{1,3}' | head -n1 || true)
    if [[ -n "${ip:-}" ]] && validate_ipv4 "$ip" >/dev/null; then
      printf '%s\n' "$ip"
      exit 0
    fi
  fi
done

# Fallback using DNS if curl endpoints fail
if command -v dig >/dev/null 2>&1; then
  if ip=$(dig +short -4 myip.opendns.com @resolver1.opendns.com | head -n1); then
    if [[ -n "$ip" ]] && validate_ipv4 "$ip" >/dev/null; then
      printf '%s\n' "$ip"
      exit 0
    fi
  fi
fi

echo "unable to determine public IPv4" >&2
exit 1