from __future__ import absolute_import

import abc
from random import choice, randint
import six
from time import time
from threading import Lock


class DiscoveryStrategy(six.with_metaclass(abc.ABCMeta, object)):
    """
    Strategy for discovering peers in a network.
    """

    def __init__(self, overlay):
        self.overlay = overlay
        self.walk_lock = Lock()

    @abc.abstractmethod
    def take_step(self, service_id=None):
        pass


class RandomWalk(DiscoveryStrategy):
    """
    Walk randomly through the network.
    """

    def __init__(self, overlay, timeout=3.0, window_size=5, reset_chance=50):
        """
        Create a new walk strategy.

        :param overlay: the Overlay to walk over
        :type overlay: Overlay
        :param timeout: the timeout (in seconds) after which peers are considered unreachable
        :type timeout: float
        :param window_size: the amount of unanswered packets we can have in-flight
        :type window_size: int
        :param reset_chance: the chance (0-255) to go back to the tracker
        :type reset_chance: int
        """
        super(RandomWalk, self).__init__(overlay)
        self.intro_timeouts = {}
        self.node_timeout = timeout
        self.window_size = window_size
        self.reset_chance = reset_chance

    def take_step(self, service_id=None):
        """
        Walk to random walkable peer.
        """
        with self.walk_lock:
            # Sanitize unreachable nodes
            to_remove = []
            for node in self.intro_timeouts:
                if self.intro_timeouts[node] + self.node_timeout < time():
                    to_remove.append(node)
            for node in to_remove:
                del self.intro_timeouts[node]
                if not self.overlay.network.get_verified_by_address(node):
                    self.overlay.network.remove_by_address(node)
            # If a valid window size (>0) is specified and we are waiting for (at least) this many pings: return
            if self.window_size and self.window_size > 0 and len(self.intro_timeouts) >= self.window_size:
                return
            # Take step
            known = self.overlay.network.get_walkable_addresses(service_id)
            available = list(set(known) - set(self.intro_timeouts.keys()))

            # We can get stuck in an infinite loop of unreachable peers if we never contact the tracker again
            if available and randint(0, 255) >= self.reset_chance:
                peer = choice(available)
                self.overlay.walk_to(peer)
                self.intro_timeouts[peer] = time()
            else:
                self.overlay.get_new_introduction(service_id=service_id)


class EdgeWalk(DiscoveryStrategy):
    """
    Walk through the network by using edges.

    This will perform a depth-first search in the network starting from your direct neighborhood.
    When a certain depth is reached, we teleport home and start again from our neighborhood.
    """

    def __init__(self, overlay, edge_length=4, neighborhood_size=6, edge_timeout=3.0):
        super(EdgeWalk, self).__init__(overlay)
        self._neighborhood = []

        self.complete_edges = []
        self.under_construction = {}
        self.last_edge_responses = {}

        self.edge_length = edge_length
        self.neighborhood_size = neighborhood_size
        self.edge_timeout = edge_timeout

    def get_available_root(self):
        """
        Get a root, if it exists, which is not busy constructing an edge for us.
        """
        available = list(set(self._neighborhood) - set(self.under_construction.keys()))
        return choice(available) if available else None

    def take_step(self, service_id=None):
        """
        Attempt to grow an edge.
        """
        with self.walk_lock:
            if not self._neighborhood or len(self._neighborhood) < self.neighborhood_size:
                # Wait for our immediate neighborhood to be discovered
                self._neighborhood = self.overlay.get_peers()[:self.neighborhood_size]
                self.overlay.bootstrap()
                for peer in self.overlay.network.get_walkable_addresses(service_id)[:self.neighborhood_size]:
                    self.overlay.walk_to(peer)
            else:
                waiting_root = self.get_available_root()
                # Make sure we have as many outstanding/actively growing edges as roots
                if waiting_root:
                    self.under_construction[waiting_root] = [waiting_root]
                    self.last_edge_responses[waiting_root] = time()
                    self.overlay.get_new_introduction(waiting_root.address, service_id=service_id)
                else:
                    # Check if our introduced peer has answered yet
                    completed = []
                    for root in self.under_construction:
                        last_verified = self.under_construction[root][-1]
                        introductions = []
                        for intro in self.overlay.network.get_introductions_from(last_verified):
                            verified = self.overlay.network.get_verified_by_address(intro)
                            if verified:
                                introductions.append(verified)
                        if introductions:
                            # We got (multiple?) introductions from this peer, add it as verified
                            self.last_edge_responses[root] = time()
                            next_in_edge = choice(introductions)
                            self.under_construction[root].append(next_in_edge)
                            if len(self.under_construction[root]) == self.edge_length:
                                # We have crawled the maximum depth, teleport home
                                self.complete_edges.append(self.under_construction[root])
                                completed.append(root)
                            else:
                                # Take this edge a step further
                                self.overlay.walk_to(next_in_edge.address)
                        elif self.last_edge_responses[root] + self.edge_timeout < time():
                            # This edge isn't growing, mark it as complete
                            if len(self.under_construction[root]) > 1:
                                self.complete_edges.append(self.under_construction[root])
                            completed.append(root)
                    for root in completed:
                        del self.under_construction[root]
