import asyncio
import ipaddress
import socket
from urllib.parse import urlsplit


class UnsafeDestination(ValueError):
    pass


async def validate_destination(url: str) -> None:
    parsed = urlsplit(url)
    if parsed.scheme not in {"http", "https"} or not parsed.hostname:
        raise UnsafeDestination("only HTTP(S) URLs with a hostname are allowed")
    if parsed.username or parsed.password:
        raise UnsafeDestination("URL credentials are not allowed")
    try:
        literal = ipaddress.ip_address(parsed.hostname)
        addresses = [literal]
    except ValueError:
        loop = asyncio.get_running_loop()
        try:
            infos = await loop.getaddrinfo(parsed.hostname, parsed.port,
                                           type=socket.SOCK_STREAM)
        except socket.gaierror as exc:
            raise UnsafeDestination("destination DNS resolution failed") from exc
        addresses = list({ipaddress.ip_address(info[4][0]) for info in infos})
    if not addresses or any(not address.is_global for address in addresses):
        raise UnsafeDestination("destination resolves to a non-public address")