import json
import sys
import time
import traceback
from abc import abstractmethod
from functools import wraps
from threading import Thread, Event, Lock
from typing import Optional, Callable, Any, Mapping
from uuid import UUID

import requests
from flask import Flask, request

from .action import ConnectionRefuse, DisconnectionRefuse, TaskRefuse, TaskFail
from ..base import random_token, ControllableService, get_http_engine_class, split_http_address, success_response, \
    failure_response, DblEvent
from ..config import DEFAULT_SLAVE_PORT, DEFAULT_CHANNEL, GLOBAL_HOST, DEFAULT_HEARTBEAT_SPAN, MIN_HEARTBEAT_SPAN, \
    DEFAULT_REQUEST_RETRIES, DEFAULT_REQUEST_RETRY_WAITING
from ..exception import SlaveErrorCode, get_slave_exception_by_error, get_master_exception_by_error


class Slave(ControllableService):
    r"""
    Overview:
        Interaction slave client
    """

    def __init__(
        self,
        host: Optional[str] = None,
        port: Optional[int] = None,
        heartbeat_span: Optional[float] = None,
        request_retries: Optional[int] = None,
        request_retry_waiting: Optional[float] = None,
        channel: Optional[int] = None
    ):
        """
        Overview:
            Constructor of Slave class
        Arguments:
            - host (:obj:`Optional[str]`): Host of the slave server, based on flask (None means `0.0.0.0`)
            - port (:obj:`Optional[int]`): Port of the slave server, based on flask (None means `7236`)
            - heartbeat_span (:obj:`Optional[float]`): Time span of heartbeat packages in seconds \
                (None means `3.0`, minimum is `0.2`)
            - request_retries (:obj:`Optional[int]`): Max times for request retries (None means `5`)
            - request_retry_waiting (:obj:`Optional[float]`): Sleep time before requests' retrying (None means `1.0`)
            - channel (:obj:`Optional[int]`): Channel id for the slave client, please make sure that channel id is \
                equal to the master client's channel id, or the connection cannot be established. (None means `0`, \
                but 0 channel is not recommended to be used in production)
        """
        # server part
        self.__host = host or GLOBAL_HOST
        self.__port = port or DEFAULT_SLAVE_PORT
        self.__flask_app_value = None
        self.__run_app_thread = Thread(target=self.__run_app, name='slave_run_app')

        # heartbeat part
        self.__heartbeat_span = max(heartbeat_span or DEFAULT_HEARTBEAT_SPAN, MIN_HEARTBEAT_SPAN)
        self.__heartbeat_thread = Thread(target=self.__heartbeat, name='slave_heartbeat')
        self.__request_retries = max(request_retries or DEFAULT_REQUEST_RETRIES, 0)
        self.__request_retry_waiting = max(request_retry_waiting or DEFAULT_REQUEST_RETRY_WAITING, 0.0)

        # task part
        self.__has_task = DblEvent()
        self.__task_lock = Lock()
        self.__task_id = None
        self.__task_data = None
        self.__task_thread = Thread(target=self.__task, name='slave_task')

        # self-connection part
        self.__self_http_engine = get_http_engine_class(
            headers={
                'Token': lambda: self.__self_token,
            },
            http_error_gene=get_slave_exception_by_error,
            # )()('localhost', self.__port, False)
        )()(self.__host, self.__port, False)  # TODO: Confirm how to ping itself
        self.__self_token = random_token()

        # master-connection part
        self.__channel = channel or DEFAULT_CHANNEL
        self.__connected = DblEvent()
        self.__master_token = None
        self.__master_address = None
        self.__master_http_engine = None

        # global part
        self.__shutdown_event = Event()
        self.__lock = Lock()

    # master connection
    def __register_master(self, token: str, address: str):
        self.__master_token = token
        self.__master_address = address
        self.__master_http_engine = get_http_engine_class(
            headers={
                'Channel': lambda: str(self.__channel),
                'Token': lambda: self.__master_token,
            },
            http_error_gene=get_master_exception_by_error,
        )()(*split_http_address(self.__master_address))

    def __unregister_master(self):
        self.__master_token = None
        self.__master_address = None
        self.__master_http_engine = None

    def __open_master_connection(self, token: str, address: str):
        self.__register_master(token, address)
        self.__connected.open()

    def __close_master_connection(self):
        self.__unregister_master()
        self.__connected.close()

    # server part
    def __generate_app(self):
        app = Flask(__name__)

        # master apis
        app.route('/connect', methods=['POST'])(self.__check_master_request(self.__connect, False))
        app.route('/disconnect', methods=['DELETE'])(self.__check_master_request(self.__disconnect, True))
        app.route('/task/new', methods=['POST'])(self.__check_master_request(self.__new_task, True))

        # self apis
        app.route('/ping', methods=['GET'])(self.__check_self_request(self.__self_ping))
        app.route('/shutdown', methods=['DELETE'])(self.__check_self_request(self.__self_shutdown))

        return app

    def __flask_app(self) -> Flask:
        return self.__flask_app_value or self.__generate_app()

    def __run_app(self):
        self.__flask_app().run(
            host=self.__host,
            port=self.__port,
        )

    # both method checkers
    def __check_shutdown(self, func: Callable[[], Any]) -> Callable[[], Any]:

        @wraps(func)
        def _func():
            if self.__shutdown_event.is_set():
                return failure_response(
                    code=SlaveErrorCode.SYSTEM_SHUTTING_DOWN, message='System has already been shutting down.'
                ), 401
            else:
                return func()

        return _func

    # server method checkers (master)
    def __check_master_request(self,
                               func: Callable[[str, Mapping[str, Any]], Any],
                               need_match: bool = True) -> Callable[[], Any]:
        return self.__check_shutdown(self.__check_channel(self.__check_master_token(func, need_match)))

    # noinspection DuplicatedCode
    def __check_channel(self, func: Callable[[], Any]) -> Callable[[], Any]:

        @wraps(func)
        def _func():
            channel = request.headers.get('Channel', None)
            channel = int(channel) if channel else None

            if channel is None:
                return failure_response(code=SlaveErrorCode.CHANNEL_NOT_FOUND, message='Channel not found.'), 400
            elif channel != self.__channel:
                return failure_response(
                    code=SlaveErrorCode.CHANNEL_INVALID, message='Channel not match with this endpoint.'
                ), 403
            else:
                return func()

        return _func

    def __check_master_token(self,
                             func: Callable[[str, Mapping[str, Any]], Any],
                             need_match: bool = True) -> Callable[[], Any]:

        @wraps(func)
        def _func():
            master_token = request.headers.get('Token', None)
            if master_token is None:
                return failure_response(
                    code=SlaveErrorCode.MASTER_TOKEN_NOT_FOUND, message='Master token not found.'
                ), 400
            elif need_match and (master_token != self.__master_token):
                return failure_response(
                    code=SlaveErrorCode.MASTER_TOKEN_INVALID, message='Master not match with this endpoint.'
                ), 403
            else:
                return func(master_token, json.loads(request.data.decode()))

        return _func

    # server method checkers (self)
    # noinspection DuplicatedCode
    def __check_self_request(self, func: Callable[[], Any]) -> Callable[[], Any]:
        return self.__check_shutdown(self.__check_slave_token(func))

    def __check_slave_token(self, func: Callable[[], Any]) -> Callable[[], Any]:

        @wraps(func)
        def _func():
            slave_token = request.headers.get('Token', None)

            if slave_token is None:
                return failure_response(code=SlaveErrorCode.SELF_TOKEN_NOT_FOUND, message='Slave token not found.'), 400
            elif slave_token != self.__self_token:
                return failure_response(
                    code=SlaveErrorCode.SELF_TOKEN_INVALID, message='Slave token not match with this endpoint.'
                ), 403
            else:
                return func()

        return _func

    # server methods (self)
    # noinspection PyMethodMayBeStatic
    def __self_ping(self):
        return success_response(message='PONG!')

    def __self_shutdown(self):
        _shutdown_func = request.environ.get('werkzeug.server.shutdown')
        if _shutdown_func is None:
            raise RuntimeError('Not running with the Werkzeug Server')

        self.__shutdown_event.set()
        _shutdown_func()

        return success_response(message='Shutdown request received, this server will be down later.')

    # server methods (master)
    # noinspection PyUnusedLocal
    def __connect(self, token: str, data: Mapping[str, Any]):
        if self.__connected.is_open():
            return failure_response(
                code=SlaveErrorCode.SLAVE_ALREADY_CONNECTED, message='This slave already connected.'
            ), 400
        else:
            _master_info, _connection_data = data['master'], data['data']

            try:
                self._before_connection(_connection_data)
            except ConnectionRefuse as err:
                return err.get_response()
            else:
                self.__open_master_connection(token, _master_info['address'])
                return success_response(message='Connect success.')

    # noinspection PyUnusedLocal
    def __new_task(self, token: str, data: Mapping[str, Any]):
        with self.__task_lock:
            if self.__has_task.is_open():
                return failure_response(code=SlaveErrorCode.TASK_ALREADY_EXIST, message='Already has a task.'), 400
            else:
                _task_info, _task_data = data['task'], data['data']
                _task_id = _task_info['id']

                try:
                    self._before_task(_task_data)
                except TaskRefuse as err:
                    return err.get_response()
                else:
                    self.__task_id = UUID(_task_id)
                    self.__task_data = _task_data
                    self.__has_task.open()
                    return success_response(message='Task received!')

    # noinspection PyUnusedLocal
    def __disconnect(self, token: str, data: Mapping[str, Any]):
        if self.__connected.is_close():
            return failure_response(
                code=SlaveErrorCode.SLAVE_NOT_CONNECTED, message='This slave not connected yet.'
            ), 400
        else:
            _disconnection_data = data['data']

            try:
                self._before_disconnection(_disconnection_data)
            except DisconnectionRefuse as err:
                return err.get_response()
            else:
                self.__close_master_connection()
                return success_response(message='Disconnect success.')

    # heartbeat part
    def __heartbeat(self):
        _last_time = time.time()
        while not self.__shutdown_event.is_set():
            if self.__connected.is_open():
                try:
                    self.__master_heartbeat()
                except requests.exceptions.RequestException as err:
                    self._lost_connection(self.__master_address, err)
                    self.__close_master_connection()
                    traceback.print_exception(*sys.exc_info(), file=sys.stderr)

            _last_time += self.__heartbeat_span
            time.sleep(max(_last_time - time.time(), 0))

    # task part
    def __task(self):
        while not self.__shutdown_event.is_set():
            self.__has_task.wait_for_open(timeout=1.0)
            if self.__has_task.is_open():
                # noinspection PyBroadException
                try:
                    result = self._process_task(self.__task_data)
                except TaskFail as fail:
                    self.__has_task.close()
                    self.__master_task_fail(fail.result)
                except Exception:
                    self.__has_task.close()
                    traceback.print_exception(*sys.exc_info(), file=sys.stderr)
                else:
                    self.__has_task.close()
                    self.__master_task_complete(result)

    # self request operations
    def __self_request(self, method: Optional[str] = 'GET', path: Optional[str] = None) -> requests.Response:
        return self.__self_http_engine.request(
            method,
            path,
            retries=self.__request_retries,
            retry_waiting=self.__request_retry_waiting,
        )

    def __ping_once(self):
        return self.__self_request('GET', '/ping')

    def __ping_until_started(self):
        while True:
            try:
                self.__ping_once()
            except (requests.exceptions.BaseHTTPError, requests.exceptions.RequestException):
                time.sleep(0.2)
            else:
                break

    def __shutdown(self):
        self.__self_request('DELETE', '/shutdown')

    # master request operations
    def __master_request(
            self,
            method: Optional[str] = 'GET',
            path: Optional[str] = None,
            data: Optional[Mapping[str, Any]] = None
    ) -> requests.Response:
        return self.__master_http_engine.request(
            method,
            path,
            data,
            retries=self.__request_retries,
            retry_waiting=self.__request_retry_waiting,
        )

    def __master_heartbeat(self):
        return self.__master_request('GET', '/slave/heartbeat')

    def __master_task_complete(self, result: Mapping[str, Any]):
        return self.__master_request(
            'PUT', '/slave/task/complete', data={
                'task': {
                    'id': str(self.__task_id)
                },
                'result': result or {},
            }
        )

    def __master_task_fail(self, result: Mapping[str, Any]):
        return self.__master_request(
            'PUT', '/slave/task/fail', data={
                'task': {
                    'id': str(self.__task_id)
                },
                'result': result or {},
            }
        )

    # public methods
    def ping(self) -> bool:
        """
        Overview:
            Ping the current http server, check if it still run properly.
        Returns:
            - output (:obj:`bool`): The http server run properly or not. \
                `True` means run properly, otherwise return `False`.
        """
        with self.__lock:
            try:
                self.__ping_once()
            except (requests.exceptions.BaseHTTPError, requests.exceptions.RequestException):
                return False
            else:
                return True

    def start(self):
        """
        Overview:
            Start current slave client
            Here are the steps executed inside in order:

                1. Start the task-processing thread
                2. Start the heartbeat thread
                3. Start the http server thread
                4. Wait until the http server is online (can be pinged)
        """
        with self.__lock:
            self.__task_thread.start()
            self.__heartbeat_thread.start()
            self.__run_app_thread.start()

            self.__ping_until_started()

    def shutdown(self):
        """
        Overview:
            Shutdown current slave client.
            A shutdown request will be sent to the http server, and the shutdown signal will be apply into the \
            threads, the server will be down soon (You can use `join` method to wait until that time).
        """
        with self.__lock:
            self.__shutdown()

    def join(self):
        """
        Overview:
            Wait until current slave client is down completely.
            Here are the steps executed inside in order:

                1. Wait until the http server thread down
                2. Wait until the heartbeat thread down
                3. Wait until the task-processing thread down
        """
        with self.__lock:
            self.__run_app_thread.join()
            self.__heartbeat_thread.join()
            self.__task_thread.join()

    # inherit method
    def _before_connection(self, data: Mapping[str, Any]):
        """
        Overview:
            Behaviours that will be executed before connection is established.
        Arguments:
            - data (:obj:`Mapping[str, Any]`): Connection data when connect to this slave, sent from master.
        Raises:
            - `ConnectionRefuse` After raise this, the connection from master end will be refused, \
                no new connection will be established.
        """
        pass

    def _before_disconnection(self, data: Mapping[str, Any]):
        """
        Overview:
            Behaviours that will be executed before disconnection is executed.
        Arguments:
            - data (:obj:`Mapping[str, Any]`): Disconnection data when disconnect with this slave, sent from master.
        Raises:
            - `DisconnectionRefuse` After raise this, the disconnection request will be refused, \
                current connection will be still exist.
        """
        pass

    def _before_task(self, data: Mapping[str, Any]):
        """
        Overview:
            Behaviours that will be executed before task is executed.
        Arguments:
            - data (:obj:`Mapping[str, Any]`): Data of the task
        Raises:
            - `TaskRefuse` After raise this, the new task will be refused.
        """
        pass

    def _lost_connection(self, master_address: str, err: requests.exceptions.RequestException):
        """
        Overview:
            Behaviours that will be executed after connection is lost.
        Arguments:
            - master_address (:obj:`str`): String address of master end
            - err (:obj:`request.exceptions.RequestException`): Http exception of this connection loss
        """
        pass

    @abstractmethod
    def _process_task(self, task: Mapping[str, Any]):
        """
        Overview:
            Execute the task, this protected method must be implement in the subclass.
        Arguments:
            - task (:obj:`Mapping[str, Any]`): Data of the task
        Raises:
            - `TaskFail` After raise this, this task will be recognized as run failed, \
                master will received the failure signal.
        Example:
            - A success task with return value (the return value will be received in master end)

            >>> def _process_task(self, task):
            >>>     print('this is task data :', task)
            >>>     return str(task)

            - A failed task with data (the data will be received in master end)

            >>> def _process_task(self, task):
            >>>     print('this is task data :', task)
            >>>     raise TaskFail(task)  # this is a failed task

            - A failed task with data and message (both will be received in master end)

            >>> def _process_task(self, task):
            >>>     print('this is task data :', task)
            >>>     raise TaskFail(task, 'this is message')  # this is a failed task with message
        """
        raise NotImplementedError