import asyncio
import os
from collections import defaultdict
from functools import partial
from pathlib import Path
import base64
from pyasn1.type import univ, char
from pyasn1.codec.der.encoder import encode


async def execute_process(*cmd, log=None, loop=None):
    '''
    Wrapper around asyncio.create_subprocess_exec.

    '''
    p = await asyncio.create_subprocess_exec(
        *cmd,
        stdin=asyncio.subprocess.PIPE,
        stdout=asyncio.subprocess.PIPE,
        stderr=asyncio.subprocess.PIPE,
        loop=loop)
    stdout, stderr = await p.communicate()
    if log:
        log.debug("Exec %s -> %d", cmd, p.returncode)
        if stdout:
            log.debug(stdout.decode('utf-8'))
        if stderr:
            log.debug(stderr.decode('utf-8'))
    return p.returncode == 0


def _read_ssh_key():
    '''
    Inner function for read_ssh_key, suitable for passing to our
    Executor.

    '''
    default_data_dir = Path(Path.home(), ".local", "share", "juju")
    juju_data = os.environ.get("JUJU_DATA", default_data_dir)
    ssh_key_path = Path(juju_data, 'ssh', 'juju_id_rsa.pub')
    with ssh_key_path.open('r') as ssh_key_file:
        ssh_key = ssh_key_file.readlines()[0].strip()
    return ssh_key


async def read_ssh_key(loop):
    '''
    Attempt to read the local juju admin's public ssh key, so that it
    can be passed on to a model.

    '''
    loop = loop or asyncio.get_event_loop()
    return await loop.run_in_executor(None, _read_ssh_key)


class IdQueue:
    """
    Wrapper around asyncio.Queue that maintains a separate queue for each ID.
    """
    def __init__(self, maxsize=0, *, loop=None):
        self._queues = defaultdict(partial(asyncio.Queue, maxsize, loop=loop))

    async def get(self, id):
        value = await self._queues[id].get()
        del self._queues[id]
        if isinstance(value, Exception):
            raise value
        return value

    async def put(self, id, value):
        await self._queues[id].put(value)

    async def put_all(self, value):
        for queue in self._queues.values():
            await queue.put(value)


async def block_until(*conditions, timeout=None, wait_period=0.5, loop=None):
    """Return only after all conditions are true.

    """
    async def _block():
        while not all(c() for c in conditions):
            await asyncio.sleep(wait_period, loop=loop)
    await asyncio.wait_for(_block(), timeout, loop=loop)


async def run_with_interrupt(task, *events, loop=None):
    """
    Awaits a task while allowing it to be interrupted by one or more
    `asyncio.Event`s.

    If the task finishes without the events becoming set, the results of the
    task will be returned.  If the event become set, the task will be cancelled
    ``None`` will be returned.

    :param task: Task to run
    :param events: One or more `asyncio.Event`s which, if set, will interrupt
        `task` and cause it to be cancelled.
    :param loop: Optional event loop to use other than the default.
    """
    loop = loop or asyncio.get_event_loop()
    task = asyncio.ensure_future(task, loop=loop)
    event_tasks = [loop.create_task(event.wait()) for event in events]
    done, pending = await asyncio.wait([task] + event_tasks,
                                       loop=loop,
                                       return_when=asyncio.FIRST_COMPLETED)
    for f in pending:
        f.cancel()  # cancel unfinished tasks
    for f in done:
        f.exception()  # prevent "exception was not retrieved" errors
    if task in done:
        return task.result()  # may raise exception
    else:
        return None


class Addrs(univ.SequenceOf):
    componentType = char.PrintableString()


class RegistrationInfo(univ.Sequence):
    """
    ASN.1 representation of:

    type RegistrationInfo struct {
    User string

        Addrs []string

        SecretKey []byte

        ControllerName string
    }
    """
    pass


def generate_user_controller_access_token(username, controller_endpoints, secret_key, controller_name):
    """" Implement in python what is currently done in GO
    https://github.com/juju/juju/blob/a5ab92ec9b7f5da3678d9ac603fe52d45af24412/cmd/juju/user/utils.go#L16

    :param username: name of the user to register
    :param controller_endpoints: juju controller endpoints list in the format <ip>:<port>
    :param secret_key: base64 encoded string of the secret-key generated by juju
    :param controller_name: name of the controller to register to.
    """

    # Secret key is returned as base64 encoded string in:
    # https://websockets.readthedocs.io/en/stable/_modules/websockets/protocol.html#WebSocketCommonProtocol.recv
    # Deconding it before marshalling into the ASN.1 message
    secret_key = base64.b64decode(secret_key)
    addr = Addrs()
    for endpoint in controller_endpoints:
        addr.append(endpoint)

    registration_string = RegistrationInfo()
    registration_string.setComponentByPosition(0, char.PrintableString(username))
    registration_string.setComponentByPosition(1, addr)
    registration_string.setComponentByPosition(2, univ.OctetString(secret_key))
    registration_string.setComponentByPosition(3, char.PrintableString(controller_name))
    registration_string = encode(registration_string)
    remainder = len(registration_string) % 3
    registration_string += b"\0" * (3 - remainder)
    return base64.urlsafe_b64encode(registration_string)