import logging

import paramiko.client as pmc

from ._sshfp_policy import SSHFPPolicy

class SSHConnection:
    """
    An SSH client connection to a remote server, with support for a proxy "jump"
    host, like OpenSSH's 'ssh -J'. Uses only SSHFP for host key verification.

    May be used as a context manager.

    :param SSHRemote remote: Remote host to connect to.
    """
    _proxy_conn   = None
    _client       = None
    _remote       = None
    _logger       = None

    def __init__(self, remote):
        self._logger = logging.getLogger('%s.%s' % (self.__class__.__name__, str(remote)))
        self._logger.debug('Connecting to remote host...')

        sock = None
        if remote.proxy_remote is not None:
            self._proxy_conn = SSHConnection(remote.proxy_remote)
            t = self._proxy_conn.get_transport()
            sock = t.open_channel('direct-tcpip', (remote.host, remote.port), ('localhost', 0))

        self._client = pmc.SSHClient()
        self._client.set_missing_host_key_policy(SSHFPPolicy())
        self._client.connect(remote.host, remote.port, remote.username,
                             sock = sock)

        self._logger.debug('Connected to remote host')
        self._remote = remote

    def close(self):
        self._logger.debug('Disconnecting from remote host')

        if self._client:
            self._client.close()
            self._client = None
        if self._proxy_conn:
            self._proxy_conn.close()
            self._proxy_conn = None

        self._logger.debug('Disconnected from remote host')

    def exec_command(self, *args, **kwargs):
        return self._client.exec_command(*args, **kwargs)
    def get_transport(self):
        return self._client.get_transport()

    def __enter__(self):
        return self
    def __exit__(self, exc_type, exc_value, traceback):
        self.close()

    def __str__(self):
        return 'ssh:%s' % str(self._remote)