"""The system's name servers and hosts file as the default resolver: with
no nserver in a configuration, names in the hosts file are answered from
it; with nserver lines it is not. Each service resolves names the way the
last of defaultresolve, sysresolve and fakeresolve before it says."""

import os
import re
import sys
import time


def hosts_path():
    if sys.platform == "win32":
        return os.path.join(os.environ.get("SystemRoot", r"C:\Windows"),
                            "System32", "drivers", "etc", "hosts")
    return "/etc/hosts"


def hosts_localhost():
    """Whether the hosts file maps localhost to 127.0.0.1 itself."""
    try:
        with open(hosts_path(), errors="replace") as f:
            for line in f:
                words = line.split("#", 1)[0].split()
                if len(words) > 1 and words[0] == "127.0.0.1" and "localhost" in [w.lower() for w in words[1:]]:
                    return True
    except OSError:
        pass
    return False


def system_nameserver():
    """Whether there is a name server for 3proxy to find: resolv.conf has
    one, or on Windows the registry is taken to."""
    if sys.platform == "win32":
        return True
    try:
        with open("/etc/resolv.conf") as f:
            return any(re.match(r"nameserver\s+[0-9a-fA-F.:]+\s*$", l.split("#")[0]) for l in f)
    except OSError:
        return False


def wait(t, port, name):
    deadline = time.time() + 5
    while time.time() < deadline:
        if t.dns_query(port, name):
            return


def run(t):
    if not hosts_localhost() or not system_nameserver():
        t.skip("no localhost in the hosts file, or no system name server")
        return

    port = t.free_port()
    t.start("sysdns", f"""
        log
        flush
        auth iponly
        allow *
        dnspr -p{port}
    """)
    wait(t, port, "localhost")
    t.eq(["127.0.0.1"], t.dns_query(port, "localhost"),
         "without nserver, a name of the hosts file is answered from it")
    t.eq(["127.0.0.1"], t.dns_query(port, "LocalHost"),
         "whatever its case")

    # with a name server configured, one that answers nothing, the hosts
    # file is not used
    other = t.free_port()
    t.start("sysdns_nserver", f"""
        log
        flush
        nserver 127.0.0.1:{t.free_port()}
        nscache 1024
        auth iponly
        allow *
        dnspr -p{other}
    """)
    wait(t, other, "localhost")
    t.ne(["127.0.0.1"], t.dns_query(other, "localhost") or [],
         "with nserver, the hosts file is not used")

    # each service resolves the way the command before it says: fake (to
    # 127.0.0.2, where the server is not), the system routines (no
    # nsrecord) or the default (the system's name servers, and nsrecord)
    fake, system, default, srv = t.free_port(), t.free_port(), t.free_port(), t.free_port()
    t.start("sysdns_modes", f"""
        log
        nscache 1024
        nsrecord only3proxy.test 127.0.0.1
        flush
        auth iponly
        allow *
        fakeresolve
        proxy -p{fake}
        sysresolve
        proxy -p{system}
        defaultresolve
        proxy -p{default}
        flush
        auth iponly
        allow *
        http echo * /echo**
        httpsrv -i127.0.0.1 -p{srv}
    """, ports=[fake, system, default, srv])
    t.eq(200, t.http(f"http://localhost:{srv}/echo", proxy=f"127.0.0.1:{default}").status,
         "defaultresolve: a name of the hosts file resolves")
    t.eq(200, t.http(f"http://only3proxy.test:{srv}/echo", proxy=f"127.0.0.1:{default}").status,
         "and an nsrecord name")
    t.eq(200, t.http(f"http://localhost:{srv}/echo", proxy=f"127.0.0.1:{system}").status,
         "sysresolve: names resolve through the system routines")
    t.ne(200, t.http(f"http://only3proxy.test:{srv}/echo", proxy=f"127.0.0.1:{system}").status,
         "which know no nsrecord name")
    t.ne(200, t.http(f"http://localhost:{srv}/echo", proxy=f"127.0.0.1:{fake}").status,
         "fakeresolve: every name is 127.0.0.2, in a service before the others")