import base64
import paramiko

def split_user(user_at_host):
    try:
        user, host = user_at_host.rsplit('@', 1)
    except ValueError:
        user, host = None, user_at_host
    assert user != '', \
        "Bad input to split_user: {user_at_host!r}".format(user_at_host=user_at_host)
    return user, host

def create_key(keytype, key):
    if keytype == 'ssh-rsa':
        return paramiko.rsakey.RSAKey(data=base64.decodestring(key))
    elif keytype == 'ssh-dss':
        return paramiko.dsskey.DSSKey(data=base64.decodestring(key))
    else:
        raise ValueError('keytype must be ssh-rsa or ssh-dsa')

def connect(user_at_host, host_key=None, keep_alive=False,
            _SSHClient=None, _create_key=None):
    user, host = split_user(user_at_host)
    if _SSHClient is None:
        _SSHClient = paramiko.SSHClient
    ssh = _SSHClient()
    if host_key is None:
    	ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
    if _create_key is None:
        _create_key = create_key

    if host_key is None:
        ssh.load_system_host_keys()
    else:
        keytype, key = host_key.split(' ', 1)
        ssh.get_host_keys().add(
            hostname=host,
            keytype=keytype,
            key=_create_key(keytype, key)
            )
        
    # just let the exceptions bubble up to caller
    ssh.connect(
        hostname=host,
        username=user,
        timeout=60,
        )
    ssh.get_transport().set_keepalive(keep_alive)
    return ssh