#!/usr/bin/env python3
# Copyright (c) Facebook, Inc. and its affiliates. All rights reserved.

import abc
import logging
from typing import Callable, Optional

import gym
import numpy as np
import reagent.core.types as rlt
import torch
from gym import spaces
from reagent.core.dataclasses import dataclass
from reagent.core.parameters import CONTINUOUS_TRAINING_ACTION_RANGE
from reagent.core.registry_meta import RegistryMeta
from reagent.training.utils import rescale_actions


# types for reference
ObsPreprocessor = Callable[[np.ndarray], rlt.FeatureData]
ServingObsPreprocessor = Callable[[np.ndarray], rlt.ServingFeatureData]
ActionExtractor = Callable[[rlt.ActorOutput], np.ndarray]
ServingActionExtractor = ActionExtractor

CONTINUOUS_MODEL_LOW = torch.tensor(CONTINUOUS_TRAINING_ACTION_RANGE[0])
CONTINUOUS_MODEL_HIGH = torch.tensor(CONTINUOUS_TRAINING_ACTION_RANGE[1])

logger = logging.getLogger(__name__)


@dataclass
class EnvWrapper(gym.core.Wrapper, metaclass=RegistryMeta):
    """Wrapper around it's environment, to simplify configuration."""

    def __post_init_post_parse__(self):
        super().__init__(self.make())
        logger.info(
            f"Env: {self.env};\n"
            f"observation_space: {self.env.observation_space};\n"
            f"action_space: {self.env.action_space};"
        )

    @abc.abstractmethod
    def make(self) -> gym.Env:
        pass

    @abc.abstractmethod
    def obs_preprocessor(self, obs: np.ndarray) -> rlt.FeatureData:
        pass

    @abc.abstractmethod
    def serving_obs_preprocessor(self, obs: np.ndarray) -> rlt.ServingFeatureData:
        pass

    def get_obs_preprocessor(self, *ctor_args, **ctor_kwargs):
        # ctor_args go to .to call
        ctor_kwargs["non_blocking"] = True
        return lambda *args, **kwargs: self.obs_preprocessor(*args, **kwargs).to(
            *ctor_args, **ctor_kwargs
        )

    def get_serving_obs_preprocessor(self):
        return lambda *args, **kwargs: self.serving_obs_preprocessor(*args, **kwargs)

    def action_extractor(self, actor_output: rlt.ActorOutput) -> torch.Tensor:
        action = actor_output.action
        action_space = self.action_space
        # Canonical rule to return one-hot encoded actions for discrete
        assert (
            len(action.shape) == 2 and action.shape[0] == 1
        ), f"{action} (shape: {action.shape}) is not a single action!"
        if isinstance(action_space, spaces.Discrete):
            # pyre-fixme[16]: `Tensor` has no attribute `argmax`.
            return action.squeeze(0).argmax()
        elif isinstance(action_space, spaces.MultiDiscrete):
            return action.squeeze(0)
        # Canonical rule to scale actions to CONTINUOUS_TRAINING_ACTION_RANGE
        elif isinstance(action_space, spaces.Box):
            assert len(action_space.shape) == 1, f"{action_space} not supported."
            return rescale_actions(
                action.squeeze(0),
                new_min=torch.tensor(action_space.low),
                new_max=torch.tensor(action_space.high),
                prev_min=CONTINUOUS_MODEL_LOW,
                prev_max=CONTINUOUS_MODEL_HIGH,
            )
        else:
            raise NotImplementedError(f"Unsupported action space: {action_space}")

    def serving_action_extractor(self, actor_output: rlt.ActorOutput) -> torch.Tensor:
        action = actor_output.action
        action_space = self.action_space
        assert (
            len(action.shape) == 2 and action.shape[0] == 1
        ), f"{action.shape} isn't (1, action_dim)"
        if isinstance(action_space, spaces.Discrete):
            # pyre-fixme[16]: `Tensor` has no attribute `argmax`.
            return action.squeeze(0).argmax().view([])
        elif isinstance(action_space, spaces.MultiDiscrete):
            return action.squeeze(0)
        elif isinstance(action_space, spaces.Box):
            assert (
                len(action_space.shape) == 1
            ), f"Unsupported Box with shape {action_space.shape}"
            return action.squeeze(0)
        else:
            raise NotImplementedError(f"Unsupported action space: {action_space}")

    def get_action_extractor(self):
        return (
            lambda *args, **kwargs: self.action_extractor(*args, **kwargs).cpu().numpy()
        )

    def get_serving_action_extractor(self):
        return (
            lambda *args, **kwargs: self.serving_action_extractor(*args, **kwargs)
            .cpu()
            .numpy()
        )

    # TODO: add more methods to simplify gym code
    # e.g. normalization, specific preprocessor, etc.
    # This can move a lot of the if statements from create_from_env methods.

    @property
    def max_steps(self) -> Optional[int]:
        possible_keys = [
            # gym should have _max_episode_steps
            "_max_episode_steps",
            # Minigrid should have max_steps
            "max_steps",
        ]
        for key in possible_keys:
            res = getattr(self.env, key, None)
            if res is not None:
                return res
        return None

    @property
    def possible_actions_mask(self) -> Optional[np.ndarray]:
        ret = getattr(self.env, "possible_actions_mask", None)
        if ret is not None:
            ret = ret.copy()
        return ret
