# Copyright 2012 Vaibhav Bajpai
# Copyright 2009 Shikhar Bhushan
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#    http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import base64
import getpass
import os
import re
import six
import sys
import socket
import threading
from binascii import hexlify

try:
    import selectors
except ImportError:
    import selectors2 as selectors

from ncclient.capabilities import Capabilities
from ncclient.logging_ import SessionLoggerAdapter

import paramiko

from ncclient.transport.errors import AuthenticationError, SSHError, SSHUnknownHostError
from ncclient.transport.session import Session
from ncclient.transport.parser import DefaultXMLParser

import logging
logger = logging.getLogger("ncclient.transport.ssh")

PORT_NETCONF_DEFAULT = 830

BUF_SIZE = 4096

#
# Define delimiters for chunks and messages for netconf 1.1 chunk enoding.
# When matched:
#
# * result.group(0) will contain whole matched string
# * result.group(1) will contain the digit string for a chunk
# * result.group(2) will be defined if '##' found
#
RE_NC11_DELIM = re.compile(br'\n(?:#([0-9]+)|(##))\n')


def default_unknown_host_cb(host, fingerprint):
    """An unknown host callback returns `True` if it finds the key acceptable, and `False` if not.

    This default callback always returns `False`, which would lead to :meth:`connect` raising a :exc:`SSHUnknownHost` exception.

    Supply another valid callback if you need to verify the host key programmatically.

    *host* is the hostname that needs to be verified

    *fingerprint* is a hex string representing the host key fingerprint, colon-delimited e.g. `"4b:69:6c:72:6f:79:20:77:61:73:20:68:65:72:65:21"`
    """
    return False


def _colonify(fp):
    fp = fp.decode('UTF-8')
    finga = fp[:2]
    for idx in range(2, len(fp), 2):
        finga += ":" + fp[idx:idx+2]
    return finga


if sys.version < '3':
    from six import StringIO
else:
    from io import BytesIO as StringIO


class SSHSession(Session):

    "Implements a :rfc:`4742` NETCONF session over SSH."

    def __init__(self, device_handler):
        capabilities = Capabilities(device_handler.get_capabilities())
        Session.__init__(self, capabilities)
        self._host = None
        self._host_keys = paramiko.HostKeys()
        self._transport = None
        self._connected = False
        self._channel = None
        self._channel_id = None
        self._channel_name = None
        self._buffer = StringIO()
        self._device_handler = device_handler
        self._message_list = []
        self._closing = threading.Event()
        self.parser = DefaultXMLParser(self)  # SAX or DOM parser

        self.logger = SessionLoggerAdapter(logger, {'session': self})

    def _dispatch_message(self, raw):
        # Provide basic response message
        self.logger.info("Received message from host")
        # Provide complete response from host at debug log level
        self.logger.debug("Received:\n%s", raw)
        return super(SSHSession, self)._dispatch_message(raw)

    def _parse(self):
        "Messages ae delimited by MSG_DELIM. The buffer could have grown by a maximum of BUF_SIZE bytes everytime this method is called. Retains state across method calls and if a byte has been read it will not be considered again."
        return self.parser._parse10()

    def load_known_hosts(self, filename=None):

        """Load host keys from an openssh :file:`known_hosts`-style file. Can
        be called multiple times.

        If *filename* is not specified, looks in the default locations i.e. :file:`~/.ssh/known_hosts` and :file:`~/ssh/known_hosts` for Windows.
        """

        if filename is None:
            filename = os.path.expanduser('~/.ssh/known_hosts')
            try:
                self._host_keys.load(filename)
            except IOError:
                # for windows
                filename = os.path.expanduser('~/ssh/known_hosts')
                try:
                    self._host_keys.load(filename)
                except IOError:
                    pass
        else:
            self._host_keys.load(filename)

    def close(self):
        self._closing.set()
        if self._transport.is_active():
            self._transport.close()

        # Wait for the transport thread to close.
        while self.is_alive() and (self is not threading.current_thread()):
            self.join(10)

        if self._channel:
            self._channel.close()
        self._channel = None
        self._connected = False

    # REMEMBER to update transport.rst if sig. changes, since it is hardcoded there
    def connect(
            self,
            host,
            port                = PORT_NETCONF_DEFAULT,
            timeout             = None,
            unknown_host_cb     = default_unknown_host_cb,
            username            = None,
            password            = None,
            key_filename        = None,
            allow_agent         = True,
            hostkey_verify      = True,
            hostkey_b64         = None,
            look_for_keys       = True,
            ssh_config          = None,
            sock_fd             = None,
            bind_addr           = None,
            sock                = None,
            keepalive           = None,
            environment         = None):

        """Connect via SSH and initialize the NETCONF session. First attempts the publickey authentication method and then password authentication.

        To disable attempting publickey authentication altogether, call with *allow_agent* and *look_for_keys* as `False`.

        *host* is the hostname or IP address to connect to

        *port* is by default 830 (PORT_NETCONF_DEFAULT), but some devices use the default SSH port of 22 so this may need to be specified

        *timeout* is an optional timeout for socket connect

        *unknown_host_cb* is called when the server host key is not recognized. It takes two arguments, the hostname and the fingerprint (see the signature of :func:`default_unknown_host_cb`)

        *username* is the username to use for SSH authentication

        *password* is the password used if using password authentication, or the passphrase to use for unlocking keys that require it

        *key_filename* is a filename where a the private key to be used can be found

        *allow_agent* enables querying SSH agent (if found) for keys

        *hostkey_verify* enables hostkey verification from ~/.ssh/known_hosts

        *hostkey_b64* only connect when server presents a public hostkey matching this (obtain from server /etc/ssh/ssh_host_*pub or ssh-keyscan)

        *look_for_keys* enables looking in the usual locations for ssh keys (e.g. :file:`~/.ssh/id_*`)

        *ssh_config* enables parsing of an OpenSSH configuration file, if set to its path, e.g. :file:`~/.ssh/config` or to True (in this case, use :file:`~/.ssh/config`).

        *sock_fd* is an already open socket which shall be used for this connection. Useful for NETCONF outbound ssh. Use host=None together with a valid sock_fd number

        *bind_addr* is a (local) source IP address to use, must be reachable from the remote device.
        
        *sock* is an already open Python socket to be used for this connection.

        *keepalive* Turn on/off keepalive packets (default is off). If this is set, after interval seconds without sending any data over the connection, a "keepalive" packet will be sent (and ignored by the remote host). This can be useful to keep connections alive over a NAT.

        *environment* a dictionary containing the name and respective values to set
        """
        if not (host or sock_fd or sock):
            raise SSHError("Missing host, socket or socket fd")

        self._host = host

        # Optionally, parse .ssh/config
        config = {}
        if ssh_config is True:
            ssh_config = "~/.ssh/config" if sys.platform != "win32" else "~/ssh/config"
        if ssh_config is not None:
            config = paramiko.SSHConfig()
            with open(os.path.expanduser(ssh_config)) as ssh_config_file_obj:
                config.parse(ssh_config_file_obj)

            # Save default Paramiko SSH port so it can be reverted
            paramiko_default_ssh_port = paramiko.config.SSH_PORT

            # Change the default SSH port to the port specified by the user so expand_variables
            # replaces %p with the passed in port rather than 22 (the defauld paramiko.config.SSH_PORT)

            paramiko.config.SSH_PORT = port

            config = config.lookup(host)

            # paramiko.config.SSHconfig::expand_variables is called by lookup so we can set the SSH port
            # back to the default
            paramiko.config.SSH_PORT = paramiko_default_ssh_port

            host = config.get("hostname", host)
            if username is None:
                username = config.get("user")
            if key_filename is None:
                key_filename = config.get("identityfile")
            if timeout is None:
                timeout = config.get("connecttimeout")
                if timeout:
                    timeout = int(timeout)

        if hostkey_verify:
            userknownhostsfile = config.get("userknownhostsfile")
            if userknownhostsfile:
                self.load_known_hosts(os.path.expanduser(userknownhostsfile))
            else:
                self.load_known_hosts()

        if username is None:
            username = getpass.getuser()

        if sock_fd is None and sock is None:
            proxycommand = config.get("proxycommand")
            if proxycommand:
                self.logger.debug("Configuring Proxy. %s", proxycommand)
                if not isinstance(proxycommand, six.string_types):
                  proxycommand = [os.path.expanduser(elem) for elem in proxycommand]
                else:
                  proxycommand = os.path.expanduser(proxycommand)
                sock = paramiko.proxy.ProxyCommand(proxycommand)
            else:
                for res in socket.getaddrinfo(host, port, socket.AF_UNSPEC, socket.SOCK_STREAM):
                    af, socktype, proto, canonname, sa = res
                    try:
                        sock = socket.socket(af, socktype, proto)
                        sock.settimeout(timeout)
                    except socket.error:
                        continue
                    try:
                        if bind_addr:
                            sock.bind((bind_addr, 0))
                        sock.connect(sa)
                    except socket.error:
                        sock.close()
                        continue
                    break
                else:
                    raise SSHError("Could not open socket to %s:%s" % (host, port))
        elif sock is None:
            if sys.version_info[0] < 3:
                s = socket.fromfd(int(sock_fd), socket.AF_INET, socket.SOCK_STREAM)
                sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM, _sock=s)
            else:
                sock = socket.fromfd(int(sock_fd), socket.AF_INET, socket.SOCK_STREAM)
            sock.settimeout(timeout)

        self._transport = paramiko.Transport(sock)
        self._transport.set_log_channel(logger.name)
        if config.get("compression") == 'yes':
            self._transport.use_compression()

        if hostkey_b64:
            # If we need to connect with a specific hostkey, negotiate for only its type
            hostkey_obj = None
            for key_cls in [paramiko.DSSKey, paramiko.Ed25519Key, paramiko.RSAKey, paramiko.ECDSAKey]:
                try:
                    hostkey_obj = key_cls(data=base64.b64decode(hostkey_b64))
                except paramiko.SSHException:
                    # Not a key of this type - try the next
                    pass
            if not hostkey_obj:
                # We've tried all known host key types and haven't found a suitable one to use - bail
                raise SSHError("Couldn't find suitable paramiko key class for host key %s" % hostkey_b64)
            self._transport._preferred_keys = [hostkey_obj.get_name()]
        elif self._host_keys:
            # Else set preferred host keys to those we possess for the host
            # (avoids situation where known_hosts contains a valid key for the host, but that key type is not selected during negotiation)
            known_host_keys_for_this_host = self._host_keys.lookup(host) or {}
            host_port = '[%s]:%s' % (host, port)
            known_host_keys_for_this_host.update(self._host_keys.lookup(host_port) or {})
            if known_host_keys_for_this_host:
                self._transport._preferred_keys = list(known_host_keys_for_this_host)

        # Connect
        try:
            self._transport.start_client()
        except paramiko.SSHException as e:
            raise SSHError('Negotiation failed: %s' % e)

        if hostkey_verify:
            server_key_obj = self._transport.get_remote_server_key()
            fingerprint = _colonify(hexlify(server_key_obj.get_fingerprint()))

            is_known_host = False

            # For looking up entries for nonstandard (22) ssh ports in known_hosts
            # we enclose host in brackets and append port number
            known_hosts_lookups = [host, '[%s]:%s' % (host, port)]

            if hostkey_b64:
                # If hostkey specified, remote host /must/ use that hostkey
                if(hostkey_obj.get_name() == server_key_obj.get_name() and hostkey_obj.asbytes() == server_key_obj.asbytes()):
                    is_known_host = True
            else:
                # Check known_hosts
                is_known_host = any(self._host_keys.check(lookup, server_key_obj) for lookup in known_hosts_lookups)

            if not is_known_host and not unknown_host_cb(host, fingerprint):
                raise SSHUnknownHostError(known_hosts_lookups[0], fingerprint)

        # Authenticating with our private key/identity
        if key_filename is None:
            key_filenames = []
        elif isinstance(key_filename, (str, bytes)):
            key_filenames = [key_filename]
        else:
            key_filenames = key_filename

        self._auth(username, password, key_filenames, allow_agent, look_for_keys)

        self._connected = True      # there was no error authenticating
        self._closing.clear()

        if keepalive:
            self._transport.set_keepalive(keepalive)

        # TODO: leopoul: Review, test, and if needed rewrite this part
        subsystem_names = self._device_handler.get_ssh_subsystem_names()
        for subname in subsystem_names:
            self._channel = self._transport.open_session()
            self._channel_id = self._channel.get_id()
            channel_name = "%s-subsystem-%s" % (subname, str(self._channel_id))
            self._channel.set_name(channel_name)
            if environment:
                try:
                    self._channel.update_environment(environment)
                except paramiko.SSHException as e:
                    self.logger.info("%s (environment update rejected)", e)
                    handle_exception = self._device_handler.handle_connection_exceptions(self)
                    # Ignore the exception, since we continue to try the different
                    # subsystem names until we find one that can connect.
                    # have to handle exception for each vendor here
                    if not handle_exception:
                        continue
            try:
                self._channel.invoke_subsystem(subname)
            except paramiko.SSHException as e:
                self.logger.info("%s (subsystem request rejected)", e)
                handle_exception = self._device_handler.handle_connection_exceptions(self)
                # Ignore the exception, since we continue to try the different
                # subsystem names until we find one that can connect.
                # have to handle exception for each vendor here
                if not handle_exception:
                    continue
            self._channel_name = self._channel.get_name()
            self._post_connect(timeout)
            # for further upcoming RPC responses, vendor can chose their
            # choice of parser. Say DOM or SAX
            self.parser = self._device_handler.get_xml_parser(self)
            return
        raise SSHError("Could not open connection, possibly due to unacceptable"
                       " SSH subsystem name.")

    def _auth(self, username, password, key_filenames, allow_agent,
              look_for_keys):
        saved_exception = None

        for key_filename in key_filenames:
            for cls in (paramiko.RSAKey, paramiko.DSSKey, paramiko.ECDSAKey, paramiko.Ed25519Key):
                try:
                    key = cls.from_private_key_file(key_filename, password)
                    self.logger.debug("Trying key %s from %s",
                                      hexlify(key.get_fingerprint()),
                                      key_filename)
                    self._transport.auth_publickey(username, key)
                    return
                except Exception as e:
                    saved_exception = e
                    self.logger.debug(e)

        if allow_agent:
            # resequence keys from agent using private key names
            prepend_agent_keys=[]
            append_agent_keys=list(paramiko.Agent().get_keys())

            for key_filename in key_filenames:
                pubkey_filename=key_filename.strip(".pub")+".pub"
                try:
                    file_key=paramiko.PublicBlob.from_file(pubkey_filename).key_blob
                except (FileNotFoundError, ValueError):
                    continue

                for idx, agent_key in enumerate(append_agent_keys):
                    if agent_key.asbytes() == file_key:
                        self.logger.debug("Prioritising SSH agent key found in %s",key_filename )
                        prepend_agent_keys.append(append_agent_keys.pop(idx))
                        break

            agent_keys=tuple(prepend_agent_keys+append_agent_keys)

            for key in agent_keys:
                try:
                    self.logger.debug("Trying SSH agent key %s",
                                      hexlify(key.get_fingerprint()))
                    self._transport.auth_publickey(username, key)
                    return
                except Exception as e:
                    saved_exception = e
                    self.logger.debug(e)

        keyfiles = []
        if look_for_keys:
            rsa_key = os.path.expanduser("~/.ssh/id_rsa")
            dsa_key = os.path.expanduser("~/.ssh/id_dsa")
            ecdsa_key = os.path.expanduser("~/.ssh/id_ecdsa")
            ed25519_key = os.path.expanduser("~/.ssh/id_ed25519")
            if os.path.isfile(rsa_key):
                keyfiles.append((paramiko.RSAKey, rsa_key))
            if os.path.isfile(dsa_key):
                keyfiles.append((paramiko.DSSKey, dsa_key))
            if os.path.isfile(ecdsa_key):
                keyfiles.append((paramiko.ECDSAKey, ecdsa_key))
            if os.path.isfile(ed25519_key):
                keyfiles.append((paramiko.Ed25519Key, ed25519_key))
            # look in ~/ssh/ for windows users:
            rsa_key = os.path.expanduser("~/ssh/id_rsa")
            dsa_key = os.path.expanduser("~/ssh/id_dsa")
            ecdsa_key = os.path.expanduser("~/ssh/id_ecdsa")
            ed25519_key = os.path.expanduser("~/ssh/id_ed25519")
            if os.path.isfile(rsa_key):
                keyfiles.append((paramiko.RSAKey, rsa_key))
            if os.path.isfile(dsa_key):
                keyfiles.append((paramiko.DSSKey, dsa_key))
            if os.path.isfile(ecdsa_key):
                keyfiles.append((paramiko.ECDSAKey, ecdsa_key))
            if os.path.isfile(ed25519_key):
                keyfiles.append((paramiko.Ed25519Key, ed25519_key))

        for cls, filename in keyfiles:
            try:
                key = cls.from_private_key_file(filename, password)
                self.logger.debug("Trying discovered key %s in %s",
                                  hexlify(key.get_fingerprint()), filename)
                self._transport.auth_publickey(username, key)
                return
            except Exception as e:
                saved_exception = e
                self.logger.debug(e)

        if password is not None:
            try:
                self._transport.auth_password(username, password)
                return
            except Exception as e:
                saved_exception = e
                self.logger.debug(e)

        if saved_exception is not None:
            # need pep-3134 to do this right
            raise AuthenticationError(repr(saved_exception))

        raise AuthenticationError("No authentication methods available")

    def _transport_read(self):
        return self._channel.recv(BUF_SIZE)

    def _transport_write(self, data):
        return self._channel.send(data)

    def _transport_register(self, selector, event):
        selector.register(self._channel, event)

    def _send_ready(self):
        return self._channel.send_ready()

    @property
    def host(self):
        """Host this session is connected to, or None if not connected."""
        if hasattr(self, '_host'):
            return self._host
        return None

    @property
    def transport(self):
        "Underlying `paramiko.Transport <http://www.lag.net/paramiko/docs/paramiko.Transport-class.html>`_ object. This makes it possible to call methods like :meth:`~paramiko.Transport.set_keepalive` on it."
        return self._transport
