# Copyright 2016 Egor Tensin <Egor.Tensin@gmail.com>
# This file is licensed under the terms of the MIT License.
# See LICENSE.txt for details.

from collections.abc import Callable
import time

import vk.error
from vk.user import UserField

class StatusTracker:
    DEFAULT_TIMEOUT = 5

    def __init__(self, api, timeout=DEFAULT_TIMEOUT):
        self._api = api
        self._timeout = timeout
        self._on_initial_status = []
        self._on_status_update = []
        self._on_connection_error = []

    def _wait_after_connection_error(self):
        time.sleep(self._timeout)

    def add_database_writer(self, writer):
        self.add_initial_status_handler(writer.on_initial_status)
        self.add_status_update_handler(writer.on_status_update)
        self.add_connection_error_handler(writer.on_connection_error)

    def add_initial_status_handler(self, fn):
        self._assert_is_callback(fn)
        self._on_initial_status.append(fn)

    def add_status_update_handler(self, fn):
        self._assert_is_callback(fn)
        self._on_status_update.append(fn)

    def add_connection_error_handler(self, fn):
        self._assert_is_callback(fn)
        self._on_connection_error.append(fn)

    @staticmethod
    def _assert_is_callback(fn):
        if not isinstance(fn, Callable):
            raise TypeError()

    _USER_FIELDS = UserField.DOMAIN, UserField.ONLINE, UserField.LAST_SEEN,

    def _query_status(self, uids):
        return {user.get_uid(): user for user in self._api.users_get(uids, self._USER_FIELDS)}

    def _notify_status(self, user):
        for fn in self._on_initial_status:
            fn(user)

    def _notify_status_update(self, user):
        for fn in self._on_status_update:
            fn(user)

    def _notify_connection_error(self, e):
        for fn in self._on_connection_error:
            fn(e)

    def _query_initial_status(self, uids):
        while True:
            try:
                return self._query_status(uids)
            except vk.error.APIConnectionError as e:
                self._notify_connection_error(e)
                self._wait_after_connection_error()

    def _query_status_updates(self, uids):
        while True:
            self._wait_after_connection_error()
            try:
                return self._query_status(uids)
            except vk.error.APIConnectionError as e:
                self._notify_connection_error(e)

    @staticmethod
    def _filter_status_updates(old_users, new_users):
        for uid, user in new_users.items():
            if old_users[uid].is_online() != user.is_online():
                old_users[uid] = user
                yield user

    def _do_loop(self, uids):
        users = self._query_initial_status(uids)
        for user in users.values():
            self._notify_status(user)
        while True:
            updated_users = self._query_status_updates(uids)
            for user in self._filter_status_updates(users, updated_users):
                self._notify_status_update(user)

    def loop(self, uids):
        try:
            self._do_loop(uids)
        except KeyboardInterrupt:
            pass