"""
This module contains the backend controller
"""
import logging
import socket
import sys
from pyqode.core.api.client import JsonTcpClient, BackendProcess
from pyqode.core.api.manager import Manager
from pyqode.core.backend import NotRunning


def _logger():
    return logging.getLogger(__name__)


class BackendManager(Manager):
    """
    The backend controller takes care of controlling the client-server
    architecture.

    It is responsible of starting the backend process and the client socket and
    exposes an API to easily control the backend:

        - start
        - stop
        - send_request

    """
    LAST_PORT = None
    LAST_PROCESS = None
    SHARE_COUNT = 0

    def __init__(self, editor):
        super(BackendManager, self).__init__(editor)
        self._process = None
        self._sockets = []
        self.server_script = None
        self.interpreter = None
        self.args = None
        self._shared = False

    @staticmethod
    def pick_free_port():
        """ Picks a free port """
        test_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        test_socket.bind(('127.0.0.1', 0))
        free_port = int(test_socket.getsockname()[1])
        test_socket.close()
        return free_port

    def start(self, script, interpreter=sys.executable, args=None,
              error_callback=None, reuse=False):
        """
        Starts the backend process.

        The backend is a python script that starts a
        :class:`pyqode.core.backend.JsonServer`. You must write the backend
        script so that you can apply your own backend configuration.

        The script can be run with a custom interpreter. The default is to use
        sys.executable.

        .. note:: This restart the backend process if it was previously
                  running.

        :param script: Path to the backend script.
        :param interpreter: The python interpreter to use to run the backend
            script. If None, sys.executable is used unless we are in a frozen
            application (frozen backends do not require an interpreter).
        :param args: list of additional command line args to use to start
            the backend process.
        :param reuse: True to reuse an existing backend process. WARNING: to
            use this, your application must have one single server script. If
            you're creating an app which supports multiple programming
            languages you will need to merge all backend scripts into one
            single script, otherwise the wrong script might be picked up).
        """
        self._shared = reuse
        if reuse and BackendManager.SHARE_COUNT:
            self._port = BackendManager.LAST_PORT
            self._process = BackendManager.LAST_PROCESS
            BackendManager.SHARE_COUNT += 1
        else:
            if self.running:
                self.stop()
            self.server_script = script
            self.interpreter = interpreter
            self.args = args
            backend_script = script.replace('.pyc', '.py')
            self._port = self.pick_free_port()
            if hasattr(sys, "frozen") and not backend_script.endswith('.py'):
                # frozen backend script on windows/mac does not need an
                # interpreter
                program = backend_script
                pgm_args = [str(self._port)]
            else:
                program = interpreter
                pgm_args = [backend_script, str(self._port)]
            if args:
                pgm_args += args
            self._process = BackendProcess(self.editor)
            if error_callback:
                self._process.error.connect(error_callback)
            self._process.start(program, pgm_args)

            if reuse:
                BackendManager.LAST_PROCESS = self._process
                BackendManager.LAST_PORT = self._port
                BackendManager.SHARE_COUNT += 1
            _logger().debug('starting backend process: %s %s', program,
                            ' '.join(pgm_args))

    def stop(self):
        """
        Stops the backend process.
        """
        if self._process is None:
            return
        if self._shared:
            BackendManager.SHARE_COUNT -= 1
            if BackendManager.SHARE_COUNT:
                return
        _logger().debug('stopping backend process')
        # close all sockets
        for s in self._sockets:
            s._callback = None
            s.close()

        self._sockets[:] = []
        # prevent crash logs from being written if we are busy killing
        # the process
        self._process._prevent_logs = True
        while self._process.state() != self._process.NotRunning:
            self._process.waitForFinished(1)
            if sys.platform == 'win32':
                # Console applications on Windows that do not run an event
                # loop, or whose event loop does not handle the WM_CLOSE
                # message, can only be terminated by calling kill().
                self._process.kill()
            else:
                self._process.terminate()
        self._process._prevent_logs = False
        _logger().debug('backend process terminated')

    def send_request(self, worker_class_or_function, args, on_receive=None):
        """
        Requests some work to be done by the backend. You can get notified of
        the work results by passing a callback (on_receive).

        :param worker_class_or_function: Worker class or function
        :param args: worker args, any Json serializable objects
        :param on_receive: an optional callback executed when we receive the
            worker's results. The callback will be called with one arguments:
            the results of the worker (object)

        :raise: backend.NotRunning if the backend process is not running.
        """
        if not self.running:
            raise NotRunning()
        else:
            _logger().debug('sending request, worker=%r' %
                            worker_class_or_function)
            # create a socket, the request will be send as soon as the socket
            # has connected
            socket = JsonTcpClient(
                self.editor, self._port, worker_class_or_function, args,
                on_receive=on_receive)
            socket.finished.connect(self._rm_socket)
            self._sockets.append(socket)

    def _rm_socket(self, socket):
        try:
            socket.close()
            self._sockets.remove(socket)
        except ValueError:
            pass

    @property
    def running(self):
        """
        Tells whether the backend process is running.

        :return: True if the process is running, otherwise False
        """
        return (self._process is not None and
                self._process.state() != self._process.NotRunning)

    @property
    def connected(self):
        """
        Checks if the client socket is connected to the backend.

        .. deprecated: Since v2.3, a socket is created per request. Checking
            for global connection status does not make any sense anymore. This
            property now returns ``running``. This will be removed in v2.5
        """
        return self.running

    @property
    def exit_code(self):
        """
        Returns the backend process exit status or None if the
        process is till running.

        """
        if self.running:
            return None
        else:
            return self._process.exitCode()
