#!/usr/bin/env python3
# Copyright (c) Facebook, Inc. and its affiliates. All rights reserved.
"""
Pocman environment first introduced in Monte-Carlo Planning in Large POMDPs by
Silver and Veness, 2010:
https://papers.nips.cc/paper/4031-monte-carlo-planning-in-large-pomdps.pdf
"""
import logging
from typing import NamedTuple

import numpy as np
from gym import Env
from gym.spaces import Box, Discrete


logger = logging.getLogger(__name__)


MINI = dict(  # noqa
    _maze=np.array(
        [[1, 1, 1, 1], [1, 0, 0, 1], [1, 0, 0, 1], [1, 1, 1, 1]], dtype=np.int8
    ),
    _num_ghosts=1,
    _ghost_range=3,
    _ghost_home=(3, 3),
    _poc_home=(0, 0),
    _smell_range=1,
    _hear_range=2,
    _power_duration=15,
    _max_step=20,
)


MICRO = dict(  # noqa
    _maze=np.array(
        [
            [1, 3, 3, 2, 3, 3],
            [3, 3, 0, 3, 0, 3],
            [3, 3, 3, 3, 3, 3],
            [1, 1, 0, 3, 0, 3],
            [1, 2, 3, 3, 3, 1],
        ],
        dtype=np.int8,
    ),
    _num_ghosts=2,
    _ghost_range=3,
    _ghost_home=(4, 4),
    _poc_home=(0, 0),
    _smell_range=1,
    _hear_range=2,
    _power_duration=15,
    _max_step=200,
)


STATE_DIM = 10


class Action:
    UP = 0
    RIGHT = 1
    DOWN = 2
    LEFT = 3


ACTIONS = [Action.UP, Action.RIGHT, Action.DOWN, Action.LEFT]
ACTION_DICT = {
    Action.UP: "UP",
    Action.RIGHT: "RIGHT",
    Action.DOWN: "DOWN",
    Action.LEFT: "LEFT",
}


class Element:
    WALL = 0
    CLEAR_WALK_WAY = 1
    POWER = 2
    FOOD_PELLET = 3


def manhattan_distance(c1, c2):
    return np.sqrt((c1.x - c2.x) ** 2 + (c1.y - c2.y) ** 2)


def opposite_direction(d):
    if d == Action.UP:
        return Action.DOWN
    if d == Action.RIGHT:
        return Action.LEFT
    if d == Action.DOWN:
        return Action.UP
    if d == Action.LEFT:
        return Action.RIGHT


class Position(NamedTuple):
    """
    The index at the left up corner is (0, 0);
    The index at the right bottom corner is (height-1, width-1)
    """

    x: int
    y: int

    def __eq__(self, pos1):
        return isinstance(pos1, Position) and pos1.x == self.x and pos1.y == self.y


class InternalState(object):
    def __init__(self):
        self.agent_pos = None
        self.ghosts = []
        self.food_pos = []
        self.power_duration = 0


# pyre-fixme[13]: Attribute `home` is never initialized.
# pyre-fixme[13]: Attribute `max_x` is never initialized.
# pyre-fixme[13]: Attribute `max_y` is never initialized.
class Ghost(object):
    max_x: int
    max_y: int
    home: Position

    def __init__(self, env, pos, direction, ghost_range):
        self.env = env
        self.pos = pos
        self.direction = direction
        self.ghost_range = ghost_range
        self.move_type = "init"

    def move(self, agent_pos, agent_in_power):
        if manhattan_distance(agent_pos, self.pos) < self.ghost_range:
            if agent_in_power > 0:
                self.move_type = "defensive"
                self._move_defensive(agent_pos)
            else:
                self.move_type = "aggressive"
                self._move_aggressive(agent_pos)
        else:
            self.move_type = "random"
            self._move_random()

    def _move_random(self):
        movable_directions = set()
        for action in ACTIONS:
            next_pos = self.env.next_pos(self.pos, action)
            if self.pos != next_pos:
                movable_directions.add(action)

        # no doubling back unless no other choice
        if (
            opposite_direction(self.direction) in movable_directions
            and len(movable_directions) > 1
        ):
            movable_directions.remove(opposite_direction(self.direction))
        d = np.random.choice(list(movable_directions))
        next_pos = self.env.next_pos(self.pos, d)
        self.update(next_pos, d)

    def _move_aggressive(self, agent_pos):
        best_dist = self.max_x + self.max_y
        best_pos = self.pos
        best_action = -1
        for a in ACTIONS:
            next_pos = self.env.next_pos(self.pos, a)
            # not movable in this action
            if next_pos == self.pos:
                continue
            dist = manhattan_distance(next_pos, agent_pos)
            if dist <= best_dist:
                best_pos = next_pos
                best_dist = dist
                best_action = a
        self.update(best_pos, best_action)

    def _move_defensive(self, agent_pos):
        best_dist = 0
        best_pos = self.pos
        best_action = -1
        for a in ACTIONS:
            next_pos = self.env.next_pos(self.pos, a)
            # not movable in this action
            if next_pos == self.pos:
                continue
            dist = manhattan_distance(next_pos, agent_pos)
            if dist >= best_dist:
                best_pos = next_pos
                best_dist = dist
                best_action = a
        self.update(best_pos, best_action)

    def update(self, pos, direction):
        self.pos = pos
        self.direction = direction

    def reset(self):
        self.pos = self.home
        self.direction = PocManEnv.random_action()
        self.move_type = "init"


def select_maze(maze):
    maze = maze.lower()
    if maze == "micro":
        return MICRO
    if maze == "mini":
        return MINI
    else:
        raise ValueError("Maze size can only be micro or mini. ")


class PocManEnv(Env):
    def __init__(self):
        self.board = select_maze("micro")
        self._get_init_state()
        self.action_space = Discrete(4)
        self.observation_space = Box(low=0, high=1, shape=(STATE_DIM,))
        self._reward_range = 100
        self.step_cnt = 0
        self.max_steps = self.board["_max_step"]

    def seed(self, seed=None):
        np.random.seed(seed)

    def _passable(self, pos):
        return self.maze[pos.x, pos.y] != Element.WALL

    def _inside(self, pos):
        if 0 <= pos.x < self.maze.shape[0] and 0 <= pos.y < self.maze.shape[1]:
            return True
        return False

    def step(self, action):
        assert self.action_space.contains(action)
        assert self.done is False
        self.step_cnt += 1

        reward = -1
        next_pos = self.next_pos(self.internal_state.agent_pos, action)
        self.internal_state.agent_pos = next_pos

        if self.internal_state.power_duration > 0:
            self.internal_state.power_duration -= 1
        agent_in_power = self.internal_state.power_duration > 0

        hit_ghost = set()
        for g, ghost in enumerate(self.internal_state.ghosts):
            # check if the ghost hits the agent before and after it moves
            if ghost.pos == self.internal_state.agent_pos:
                hit_ghost.add(g)
            else:
                ghost.move(self.internal_state.agent_pos, agent_in_power)
                if ghost.pos == self.internal_state.agent_pos:
                    hit_ghost.add(g)

        hit_ghost = list(hit_ghost)
        for g in hit_ghost:
            if self.internal_state.power_duration > 0:
                reward += 25
                self.internal_state.ghosts[g].reset()
            else:
                reward += -100
                self.done = True
                break

        if self.step_cnt > self.board["_max_step"]:
            self.done = True

        if self._agent_at_food():
            reward += 10
            self.maze[
                self.internal_state.agent_pos.x, self.internal_state.agent_pos.y
            ] = Element.CLEAR_WALK_WAY
            if self._food_left() == 0:
                self.done = True

        if self._agent_at_power():
            self.internal_state.power_duration = self.board["_power_duration"]
            self.maze[
                self.internal_state.agent_pos.x, self.internal_state.agent_pos.y
            ] = Element.CLEAR_WALK_WAY
            reward += 10

        ob = self._make_ob()

        return ob, reward, self.done, {"state": self.internal_state}

    def _agent_at_food(self):
        agent_pos = self.internal_state.agent_pos
        if self.maze[agent_pos.x, agent_pos.y] == Element.FOOD_PELLET:
            return True
        return False

    def _agent_at_power(self):
        agent_pos = self.internal_state.agent_pos
        if self.maze[agent_pos.x, agent_pos.y] == Element.POWER:
            return True
        return False

    def _make_ob(self):
        """
        Return 10 state features of observation:
        4 features indicating whether the agent can see a ghost
            in that direction (UP, RIGHT, DOWN, LEFT)
        4 features indicating whether he can feel a wall in each of the
            cardinal directions, which is set to 1 if he is adjacent to a wall
        1 feature indicating whether he can hear a ghost, which is set to 1
            if he is within Manhattan distance 2 of a ghost
        1 feature indicating whether he can smell food (adjacent or
            diagonally adjacent to any food)
        """
        ob = np.zeros(STATE_DIM)
        for i, action in enumerate(ACTIONS):
            ob[i] = self._see_ghost(action)
            next_pos = self.next_pos(self.internal_state.agent_pos, action)
            # If an agent couldn't move from the current position, then there is a wall
            if next_pos == self.internal_state.agent_pos:
                ob[i + len(ACTIONS)] = 1
        if self._hear_ghost():
            ob[2 * len(ACTIONS)] = 1
        if self._smell_food():
            ob[2 * len(ACTIONS) + 1] = 1
        return ob

    def _see_ghost(self, action):
        distances = []
        agent_pos = self.internal_state.agent_pos
        for ghost in self.internal_state.ghosts:
            if agent_pos.x != ghost.pos.x and agent_pos.y != ghost.pos.y:
                continue
            if agent_pos == ghost.pos:
                distances.append(0)
                break
            if (
                (
                    action == Action.UP
                    and ghost.pos.x < agent_pos.x
                    and ghost.pos.y == agent_pos.y
                )
                or (
                    action == Action.DOWN
                    and ghost.pos.x > agent_pos.x
                    and ghost.pos.y == agent_pos.y
                )
                or (
                    action == Action.LEFT
                    and ghost.pos.y < agent_pos.y
                    and ghost.pos.x == agent_pos.x
                )
                or (
                    action == Action.RIGHT
                    and ghost.pos.y > agent_pos.y
                    and ghost.pos.x == agent_pos.x
                )
            ) and not self._wall_between(agent_pos, ghost.pos):
                distances.append(manhattan_distance(agent_pos, ghost.pos))
        if not distances:
            return -1
        return 1
        # the environment can also be adapted to return a real-valued distance
        # return min(distances)

    def _smell_food(self):
        smell_range = self.board["_smell_range"]
        agent_pos = self.internal_state.agent_pos

        for x in range(-smell_range, smell_range + 1):
            for y in range(-smell_range, smell_range + 1):
                smell_x = agent_pos.x + x
                smell_y = agent_pos.y + y
                if (
                    0 <= smell_x < self.maze.shape[0]
                    and 0 <= smell_y < self.maze.shape[1]
                    and self.maze[smell_x, smell_y] == Element.FOOD_PELLET
                ):
                    return True
        return False

    def _hear_ghost(self):
        for ghost in self.internal_state.ghosts:
            if (
                manhattan_distance(ghost.pos, self.internal_state.agent_pos)
                <= self.board["_hear_range"]
            ):
                return True
        return False

    def _wall_between(self, pos1, pos2):
        if pos1 == pos2:
            return False
        assert pos1.x == pos2.x or pos1.y == pos2.y
        if pos1.y == pos2.y:
            for i in range(min(pos1.x, pos2.x) + 1, max(pos1.x, pos2.x)):
                if self.maze[i, pos1.y] == Element.WALL:
                    return True
        elif pos1.x == pos2.x:
            for i in range(min(pos1.y, pos2.y), max(pos1.y, pos2.y)):
                if self.maze[pos1.x, i] == Element.WALL:
                    return True
        return False

    def _food_left(self):
        return np.sum(self.maze == Element.FOOD_PELLET)

    @staticmethod
    def random_action():
        return np.random.randint(0, 4)

    @staticmethod
    def print_action(action):
        return ACTION_DICT[action]

    def reset(self):
        self.done = False
        self.step_cnt = 0
        self._get_init_state()
        ob = self._make_ob()
        return ob

    def _get_init_state(self):
        self.maze = self.board["_maze"].copy()
        self.internal_state = InternalState()
        self.internal_state.agent_pos = Position(*self.board["_poc_home"])
        Ghost.max_x = self.maze.shape[0]
        Ghost.max_y = self.maze.shape[1]
        ghost_home = Position(*self.board["_ghost_home"])
        Ghost.home = ghost_home

        for _ in range(self.board["_num_ghosts"]):
            pos = Position(ghost_home.x, ghost_home.y)
            self.internal_state.ghosts.append(
                Ghost(
                    self,
                    pos,
                    direction=self.random_action(),
                    ghost_range=self.board["_ghost_range"],
                )
            )

        return self.internal_state

    def next_pos(self, pos, action):
        x_offset, y_offset = 0, 0
        if action == Action.UP:
            x_offset = -1
            y_offset = 0
        elif action == Action.DOWN:
            x_offset = 1
            y_offset = 0
        elif action == Action.RIGHT:
            x_offset = 0
            y_offset = 1
        elif action == Action.LEFT:
            x_offset = 0
            y_offset = -1

        next_pos = Position(pos.x + x_offset, pos.y + y_offset)

        if self._inside(next_pos) and self._passable(next_pos):
            return next_pos
        else:
            return pos

    def print_internal_state(self):
        print("Step", self.step_cnt)
        print_maze = self.maze.astype(str)
        print_maze[
            self.internal_state.agent_pos.x, self.internal_state.agent_pos.y
        ] = "A"
        ghost_str = ""
        for g, ghost in enumerate(self.internal_state.ghosts):
            print_maze[ghost.pos.x, ghost.pos.y] = "G"
            ghost_str += "Ghost {} at {}, direction={}, type={}\n".format(
                g, ghost.pos, ACTION_DICT[ghost.direction], ghost.move_type
            )
        np.set_printoptions(formatter={"str_kind": lambda x: x})
        print("Maze: \n{}".format(print_maze))
        print(
            "Agent at {}, power duration {}".format(
                self.internal_state.agent_pos, self.internal_state.power_duration
            )
        )
        print(ghost_str[:-1])

    def print_ob(self, ob):
        ob_str = ""
        for i, action in enumerate(ACTIONS):
            if ob[i] >= 0:
                ob_str += " SEE GHOST {},".format(ACTION_DICT[action])
        for i, action in enumerate(ACTIONS):
            if ob[i + len(ACTIONS)] == 1:
                ob_str += " FEEL WALL {},".format(ACTION_DICT[action])
        if ob[-2]:
            ob_str += " HEAR GHOST,"
        if ob[-1]:
            ob_str += " SMELL FOOD,"
        return ob_str
