# Copyright (c) 2011-2015 Denis Bilenko. See LICENSE for details.
"""
c-ares based hostname resolver.
"""
from __future__ import absolute_import
import os
import sys
from _socket import getservbyname, getaddrinfo, gaierror, error
from gevent.hub import Waiter, get_hub, string_types, text_type, integer_types, reraise, PY3
from gevent.socket import AF_UNSPEC, AF_INET, AF_INET6, SOCK_STREAM, SOCK_DGRAM, SOCK_RAW, AI_NUMERICHOST, EAI_SERVICE, AI_PASSIVE
from gevent.ares import channel, InvalidIP


__all__ = ['Resolver']


class Resolver(object):
    """
    Implementation of the resolver API using the `c-ares`_ library.

    This implementation uses the c-ares library to handle name
    resolution. c-ares is natively asynchronous at the socket level
    and so integrates well into gevent's event loop.

    In comparison to :class:`gevent.resolver_thread.Resolver`, the
    implementation is much more complex. In addition, there have been
    reports of it not properly honoring certain system configurations.
    However, because it does not use threads, it may scale better.

    .. caution:: This module is considered extremely experimental on PyPy, and
       due to its implementation in cython, it may be slower. It may also lead to
       interpreter crashes.

    .. _c-ares: http://c-ares.haxx.se
    """

    ares_class = channel

    def __init__(self, hub=None, use_environ=True, **kwargs):
        if hub is None:
            hub = get_hub()
        self.hub = hub
        if use_environ:
            for key in os.environ:
                if key.startswith('GEVENTARES_'):
                    name = key[11:].lower()
                    if name:
                        value = os.environ[key]
                        kwargs.setdefault(name, value)
        self.ares = self.ares_class(hub.loop, **kwargs)
        self.pid = os.getpid()
        self.params = kwargs
        self.fork_watcher = hub.loop.fork(ref=False)
        self.fork_watcher.start(self._on_fork)

    def __repr__(self):
        return '<gevent.resolver_ares.Resolver at 0x%x ares=%r>' % (id(self), self.ares)

    def _on_fork(self):
        # NOTE: See comment in gevent.hub.reinit.
        pid = os.getpid()
        if pid != self.pid:
            self.hub.loop.run_callback(self.ares.destroy)
            self.ares = self.ares_class(self.hub.loop, **self.params)
            self.pid = pid

    def close(self):
        if self.ares is not None:
            self.hub.loop.run_callback(self.ares.destroy)
            self.ares = None
        self.fork_watcher.stop()

    def gethostbyname(self, hostname, family=AF_INET):
        hostname = _resolve_special(hostname, family)
        return self.gethostbyname_ex(hostname, family)[-1][0]

    def gethostbyname_ex(self, hostname, family=AF_INET):
        if PY3:
            if isinstance(hostname, str):
                hostname = hostname.encode('idna')
            elif not isinstance(hostname, (bytes, bytearray)):
                raise TypeError('Expected es(idna), not %s' % type(hostname).__name__)
        else:
            if isinstance(hostname, text_type):
                hostname = hostname.encode('ascii')
            elif not isinstance(hostname, str):
                raise TypeError('Expected string, not %s' % type(hostname).__name__)

        while True:
            ares = self.ares
            try:
                waiter = Waiter(self.hub)
                ares.gethostbyname(waiter, hostname, family)
                result = waiter.get()
                if not result[-1]:
                    raise gaierror(-5, 'No address associated with hostname')
                return result
            except gaierror:
                if ares is self.ares:
                    raise
                # "self.ares is not ares" means channel was destroyed (because we were forked)

    def _lookup_port(self, port, socktype):
        socktypes = []
        if isinstance(port, string_types):
            try:
                port = int(port)
            except ValueError:
                try:
                    if socktype == 0:
                        origport = port
                        try:
                            port = getservbyname(port, 'tcp')
                            socktypes.append(SOCK_STREAM)
                        except error:
                            port = getservbyname(port, 'udp')
                            socktypes.append(SOCK_DGRAM)
                        else:
                            try:
                                if port == getservbyname(origport, 'udp'):
                                    socktypes.append(SOCK_DGRAM)
                            except error:
                                pass
                    elif socktype == SOCK_STREAM:
                        port = getservbyname(port, 'tcp')
                    elif socktype == SOCK_DGRAM:
                        port = getservbyname(port, 'udp')
                    else:
                        raise gaierror(EAI_SERVICE, 'Servname not supported for ai_socktype')
                except error as ex:
                    if 'not found' in str(ex):
                        raise gaierror(EAI_SERVICE, 'Servname not supported for ai_socktype')
                    else:
                        raise gaierror(str(ex))
                except UnicodeEncodeError:
                    raise error('Int or String expected')
        elif port is None:
            port = 0
        elif isinstance(port, integer_types):
            pass
        else:
            raise error('Int or String expected', port, type(port))
        port = int(port % 65536)
        if not socktypes and socktype:
            socktypes.append(socktype)
        return port, socktypes

    def _getaddrinfo(self, host, port, family=0, socktype=0, proto=0, flags=0):
        if isinstance(host, text_type):
            host = host.encode('idna')
        elif not isinstance(host, str) or (flags & AI_NUMERICHOST):
            # this handles cases which do not require network access
            # 1) host is None
            # 2) host is of an invalid type
            # 3) AI_NUMERICHOST flag is set
            return getaddrinfo(host, port, family, socktype, proto, flags)
            # we also call _socket.getaddrinfo below if family is not one of AF_*

        port, socktypes = self._lookup_port(port, socktype)

        socktype_proto = [(SOCK_STREAM, 6), (SOCK_DGRAM, 17), (SOCK_RAW, 0)]
        if socktypes:
            socktype_proto = [(x, y) for (x, y) in socktype_proto if x in socktypes]
        if proto:
            socktype_proto = [(x, y) for (x, y) in socktype_proto if proto == y]

        ares = self.ares

        if family == AF_UNSPEC:
            values = Values(self.hub, 2)
            ares.gethostbyname(values, host, AF_INET)
            ares.gethostbyname(values, host, AF_INET6)
        elif family == AF_INET:
            values = Values(self.hub, 1)
            ares.gethostbyname(values, host, AF_INET)
        elif family == AF_INET6:
            values = Values(self.hub, 1)
            ares.gethostbyname(values, host, AF_INET6)
        else:
            raise gaierror(5, 'ai_family not supported: %r' % (family, ))

        values = values.get()
        if len(values) == 2 and values[0] == values[1]:
            values.pop()

        result = []
        result4 = []
        result6 = []

        for addrs in values:
            if addrs.family == AF_INET:
                for addr in addrs[-1]:
                    sockaddr = (addr, port)
                    for socktype, proto in socktype_proto:
                        result4.append((AF_INET, socktype, proto, '', sockaddr))
            elif addrs.family == AF_INET6:
                for addr in addrs[-1]:
                    if addr == '::1':
                        dest = result
                    else:
                        dest = result6
                    sockaddr = (addr, port, 0, 0)
                    for socktype, proto in socktype_proto:
                        dest.append((AF_INET6, socktype, proto, '', sockaddr))

        result += result4 + result6

        if not result:
            raise gaierror(-5, 'No address associated with hostname')

        return result

    def getaddrinfo(self, host, port, family=0, socktype=0, proto=0, flags=0):
        while True:
            ares = self.ares
            try:
                return self._getaddrinfo(host, port, family, socktype, proto, flags)
            except gaierror:
                if ares is self.ares:
                    raise

    def _gethostbyaddr(self, ip_address):
        if PY3:
            if isinstance(ip_address, str):
                ip_address = ip_address.encode('idna')
            elif not isinstance(ip_address, (bytes, bytearray)):
                raise TypeError('Expected es(idna), not %s' % type(ip_address).__name__)
        else:
            if isinstance(ip_address, text_type):
                ip_address = ip_address.encode('ascii')
            elif not isinstance(ip_address, str):
                raise TypeError('Expected string, not %s' % type(ip_address).__name__)

        waiter = Waiter(self.hub)
        try:
            self.ares.gethostbyaddr(waiter, ip_address)
            return waiter.get()
        except InvalidIP:
            result = self._getaddrinfo(ip_address, None, family=AF_UNSPEC, socktype=SOCK_DGRAM)
            if not result:
                raise
            _ip_address = result[0][-1][0]
            if isinstance(_ip_address, text_type):
                _ip_address = _ip_address.encode('ascii')
            if _ip_address == ip_address:
                raise
            waiter.clear()
            self.ares.gethostbyaddr(waiter, _ip_address)
            return waiter.get()

    def gethostbyaddr(self, ip_address):
        ip_address = _resolve_special(ip_address, AF_UNSPEC)
        while True:
            ares = self.ares
            try:
                return self._gethostbyaddr(ip_address)
            except gaierror:
                if ares is self.ares:
                    raise

    def _getnameinfo(self, sockaddr, flags):
        if not isinstance(flags, int):
            raise TypeError('an integer is required')
        if not isinstance(sockaddr, tuple):
            raise TypeError('getnameinfo() argument 1 must be a tuple')

        address = sockaddr[0]
        if not PY3 and isinstance(address, text_type):
            address = address.encode('ascii')

        if not isinstance(address, string_types):
            raise TypeError('sockaddr[0] must be a string, not %s' % type(address).__name__)

        port = sockaddr[1]
        if not isinstance(port, int):
            raise TypeError('port must be an integer, not %s' % type(port))

        waiter = Waiter(self.hub)
        result = self._getaddrinfo(address, str(sockaddr[1]), family=AF_UNSPEC, socktype=SOCK_DGRAM)
        if not result:
            reraise(*sys.exc_info())
        elif len(result) != 1:
            raise error('sockaddr resolved to multiple addresses')
        family, socktype, proto, name, address = result[0]

        if family == AF_INET:
            if len(sockaddr) != 2:
                raise error("IPv4 sockaddr must be 2 tuple")
        elif family == AF_INET6:
            address = address[:2] + sockaddr[2:]

        self.ares.getnameinfo(waiter, address, flags)
        node, service = waiter.get()
        if service is None:
            service = '0'
        return node, service

    def getnameinfo(self, sockaddr, flags):
        while True:
            ares = self.ares
            try:
                return self._getnameinfo(sockaddr, flags)
            except gaierror:
                if ares is self.ares:
                    raise


class Values(object):
    # helper to collect multiple values; ignore errors unless nothing has succeeded
    # QQQ could probably be moved somewhere - hub.py?

    __slots__ = ['count', 'values', 'error', 'waiter']

    def __init__(self, hub, count):
        self.count = count
        self.values = []
        self.error = None
        self.waiter = Waiter(hub)

    def __call__(self, source):
        self.count -= 1
        if source.exception is None:
            self.values.append(source.value)
        else:
            self.error = source.exception
        if self.count <= 0:
            self.waiter.switch()

    def get(self):
        self.waiter.get()
        if self.values:
            return self.values
        else:
            raise self.error


def _resolve_special(hostname, family):
    if hostname == '':
        result = getaddrinfo(None, 0, family, SOCK_DGRAM, 0, AI_PASSIVE)
        if len(result) != 1:
            raise error('wildcard resolved to multiple address')
        return result[0][4][0]
    return hostname