from mailu import models
from flask import current_app as app

import re
import urllib
import ipaddress
import socket
import sqlalchemy.exc
import tenacity

SUPPORTED_AUTH_METHODS = ["none", "plain"]


STATUSES = {
    "authentication": ("Authentication credentials invalid", {
        "imap": "AUTHENTICATIONFAILED",
        "smtp": "535 5.7.8",
        "pop3": "-ERR Authentication failed"
    }),
    "encryption": ("Must issue a STARTTLS command first", {
        "smtp": "530 5.7.0"
    }),
    "ratelimit": ("Temporary authentication failure (rate-limit)", {
        "imap": "LIMIT",
        "smtp": "451 4.3.2",
        "pop3": "-ERR [LOGIN-DELAY] Retry later"
    }),
}

def check_credentials(user, password, ip, protocol=None):
    if not user or not user.enabled or (protocol == "imap" and not user.enable_imap) or (protocol == "pop3" and not user.enable_pop):
        return False
    is_ok = False
    # webmails
    if len(password) == 64 and ip == app.config['WEBMAIL_ADDRESS']:
        if user.verify_temp_token(password):
            is_ok = True
    # All tokens are 32 characters hex lowercase
    if not is_ok and len(password) == 32:
        for token in user.tokens:
            if (token.check_password(password) and
                (not token.ip or token.ip == ip)):
                    is_ok = True
                    break
    if not is_ok and user.check_password(password):
        is_ok = True
    return is_ok

def handle_authentication(headers):
    """ Handle an HTTP nginx authentication request
    See: http://nginx.org/en/docs/mail/ngx_mail_auth_http_module.html#protocol
    """
    method = headers["Auth-Method"]
    protocol = headers["Auth-Protocol"]
    # Incoming mail, no authentication
    if method == "none" and protocol == "smtp":
        server, port = get_server(protocol, False)
        if app.config["INBOUND_TLS_ENFORCE"]:
            if "Auth-SSL" in headers and headers["Auth-SSL"] == "on":
                return {
                    "Auth-Status": "OK",
                    "Auth-Server": server,
                    "Auth-Port": port
                }
            else:
                status, code = get_status(protocol, "encryption")
                return {
                    "Auth-Status": status,
                    "Auth-Error-Code" : code,
                    "Auth-Wait": 0
                }
        else:
            return {
                "Auth-Status": "OK",
                "Auth-Server": server,
                "Auth-Port": port
            }
    # Authenticated user
    elif method == "plain":
        is_valid_user = False
        if headers["Auth-Port"] == '25':
            return {
                "Auth-Status": "AUTH not supported",
                "Auth-Error-Code": "502 5.5.1",
                "Auth-Wait": 0
            }
        # According to RFC2616 section 3.7.1 and PEP 3333, HTTP headers should
        # be ASCII and are generally considered ISO8859-1. However when passing
        # the password, nginx does not transcode the input UTF string, thus
        # we need to manually decode.
        raw_user_email = urllib.parse.unquote(headers["Auth-User"])
        raw_password = urllib.parse.unquote(headers["Auth-Pass"])
        user_email = 'invalid'
        try:
            user_email = raw_user_email.encode("iso8859-1").decode("utf8")
            password = raw_password.encode("iso8859-1").decode("utf8")
            ip = urllib.parse.unquote(headers["Client-Ip"])
        except:
            app.logger.warn(f'Received undecodable user/password from nginx: {raw_user_email!r}/{raw_password!r}')
        else:
            try:
                user = models.User.query.get(user_email)
                is_valid_user = True
            except sqlalchemy.exc.StatementError as exc:
                exc = str(exc).split('\n', 1)[0]
                app.logger.warn(f'Invalid user {user_email!r}: {exc}')
            else:
                ip = urllib.parse.unquote(headers["Client-Ip"])
                if check_credentials(user, password, ip, protocol):
                    server, port = get_server(headers["Auth-Protocol"], True)
                    return {
                        "Auth-Status": "OK",
                        "Auth-Server": server,
                        "Auth-User": user_email,
                        "Auth-User-Exists": is_valid_user,
                        "Auth-Port": port
                    }
        status, code = get_status(protocol, "authentication")
        return {
            "Auth-Status": status,
            "Auth-Error-Code": code,
            "Auth-User": user_email,
            "Auth-User-Exists": is_valid_user,
            "Auth-Wait": 0
        }
    # Unexpected
    return {}


def get_status(protocol, status):
    """ Return the proper error code depending on the protocol
    """
    status, codes = STATUSES[status]
    return status, codes[protocol]

def extract_host_port(host_and_port, default_port):
    host, _, port = re.match('^(.*?)(:([0-9]*))?$', host_and_port).groups()
    return host, int(port) if port else default_port

def get_server(protocol, authenticated=False):
    if protocol == "imap":
        hostname, port = extract_host_port(app.config['IMAP_ADDRESS'], 143)
    elif protocol == "pop3":
        hostname, port = extract_host_port(app.config['POP3_ADDRESS'], 110)
    elif protocol == "smtp":
        if authenticated:
            hostname, port = extract_host_port(app.config['AUTHSMTP_ADDRESS'], 10025)
        else:
            hostname, port = extract_host_port(app.config['SMTP_ADDRESS'], 25)
    try:
        # test if hostname is already resolved to an ip adddress
        ipaddress.ip_address(hostname)
    except:
        # hostname is not an ip address - so we need to resolve it
        hostname = resolve_hostname(hostname)
    return hostname, port

@tenacity.retry(stop=tenacity.stop_after_attempt(100),
                wait=tenacity.wait_random(min=2, max=5))
def resolve_hostname(hostname):
    """ This function uses system DNS to resolve a hostname.
    It is capable of retrying in case the host is not immediately available
    """
    return socket.gethostbyname(hostname)