"""An example of customizing PPO to leverage a centralized critic.

Here the model and policy are hard-coded to implement a centralized critic
for TwoStepGame, but you can adapt this for your own use cases.

Compared to simply running `rllib/examples/two_step_game.py --run=PPO`,
this centralized critic version reaches vf_explained_variance=1.0 more stably
since it takes into account the opponent actions as well as the policy's.
Note that this is also using two independent policies instead of weight-sharing
with one.

See also: centralized_critic_2.py for a simpler approach that instead
modifies the environment.
"""

import argparse
import numpy as np
from gym.spaces import Discrete
import os

import ray
from ray import tune
from ray.rllib.agents.maml.maml_torch_policy import KLCoeffMixin as TorchKLCoeffMixin
from ray.rllib.agents.ppo.ppo import PPOTrainer
from ray.rllib.agents.ppo.ppo_tf_policy import (
    PPOTFPolicy,
    KLCoeffMixin,
    ppo_surrogate_loss as tf_loss,
)
from ray.rllib.agents.ppo.ppo_torch_policy import PPOTorchPolicy
from ray.rllib.evaluation.postprocessing import compute_advantages, Postprocessing
from ray.rllib.examples.env.two_step_game import TwoStepGame
from ray.rllib.examples.models.centralized_critic_models import (
    CentralizedCriticModel,
    TorchCentralizedCriticModel,
)
from ray.rllib.models import ModelCatalog
from ray.rllib.policy.sample_batch import SampleBatch
from ray.rllib.policy.tf_policy import LearningRateSchedule, EntropyCoeffSchedule
from ray.rllib.policy.torch_policy import (
    LearningRateSchedule as TorchLR,
    EntropyCoeffSchedule as TorchEntropyCoeffSchedule,
)
from ray.rllib.utils.annotations import override
from ray.rllib.utils.framework import try_import_tf, try_import_torch
from ray.rllib.utils.test_utils import check_learning_achieved
from ray.rllib.utils.tf_utils import explained_variance, make_tf_callable
from ray.rllib.utils.torch_utils import convert_to_torch_tensor

tf1, tf, tfv = try_import_tf()
torch, nn = try_import_torch()

OPPONENT_OBS = "opponent_obs"
OPPONENT_ACTION = "opponent_action"

parser = argparse.ArgumentParser()
parser.add_argument(
    "--framework",
    choices=["tf", "tf2", "tfe", "torch"],
    default="tf",
    help="The DL framework specifier.",
)
parser.add_argument(
    "--as-test",
    action="store_true",
    help="Whether this script should be run as a test: --stop-reward must "
    "be achieved within --stop-timesteps AND --stop-iters.",
)
parser.add_argument(
    "--stop-iters", type=int, default=100, help="Number of iterations to train."
)
parser.add_argument(
    "--stop-timesteps", type=int, default=100000, help="Number of timesteps to train."
)
parser.add_argument(
    "--stop-reward", type=float, default=7.99, help="Reward at which we stop training."
)


class CentralizedValueMixin:
    """Add method to evaluate the central value function from the model."""

    def __init__(self):
        if self.config["framework"] != "torch":
            self.compute_central_vf = make_tf_callable(self.get_session())(
                self.model.central_value_function
            )
        else:
            self.compute_central_vf = self.model.central_value_function


# Grabs the opponent obs/act and includes it in the experience train_batch,
# and computes GAE using the central vf predictions.
def centralized_critic_postprocessing(
    policy, sample_batch, other_agent_batches=None, episode=None
):
    pytorch = policy.config["framework"] == "torch"
    if (pytorch and hasattr(policy, "compute_central_vf")) or (
        not pytorch and policy.loss_initialized()
    ):
        assert other_agent_batches is not None
        [(_, opponent_batch)] = list(other_agent_batches.values())

        # also record the opponent obs and actions in the trajectory
        sample_batch[OPPONENT_OBS] = opponent_batch[SampleBatch.CUR_OBS]
        sample_batch[OPPONENT_ACTION] = opponent_batch[SampleBatch.ACTIONS]

        # overwrite default VF prediction with the central VF
        if args.framework == "torch":
            sample_batch[SampleBatch.VF_PREDS] = (
                policy.compute_central_vf(
                    convert_to_torch_tensor(
                        sample_batch[SampleBatch.CUR_OBS], policy.device
                    ),
                    convert_to_torch_tensor(sample_batch[OPPONENT_OBS], policy.device),
                    convert_to_torch_tensor(
                        sample_batch[OPPONENT_ACTION], policy.device
                    ),
                )
                .cpu()
                .detach()
                .numpy()
            )
        else:
            sample_batch[SampleBatch.VF_PREDS] = policy.compute_central_vf(
                sample_batch[SampleBatch.CUR_OBS],
                sample_batch[OPPONENT_OBS],
                sample_batch[OPPONENT_ACTION],
            )
    else:
        # Policy hasn't been initialized yet, use zeros.
        sample_batch[OPPONENT_OBS] = np.zeros_like(sample_batch[SampleBatch.CUR_OBS])
        sample_batch[OPPONENT_ACTION] = np.zeros_like(sample_batch[SampleBatch.ACTIONS])
        sample_batch[SampleBatch.VF_PREDS] = np.zeros_like(
            sample_batch[SampleBatch.REWARDS], dtype=np.float32
        )

    completed = sample_batch["dones"][-1]
    if completed:
        last_r = 0.0
    else:
        last_r = sample_batch[SampleBatch.VF_PREDS][-1]

    train_batch = compute_advantages(
        sample_batch,
        last_r,
        policy.config["gamma"],
        policy.config["lambda"],
        use_gae=policy.config["use_gae"],
    )
    return train_batch


# Copied from PPO but optimizing the central value function.
def loss_with_central_critic(policy, model, dist_class, train_batch):
    CentralizedValueMixin.__init__(policy)
    func = tf_loss if not policy.config["framework"] == "torch" else PPOTorchPolicy.loss

    vf_saved = model.value_function
    model.value_function = lambda: policy.model.central_value_function(
        train_batch[SampleBatch.CUR_OBS],
        train_batch[OPPONENT_OBS],
        train_batch[OPPONENT_ACTION],
    )

    policy._central_value_out = model.value_function()
    loss = func(policy, model, dist_class, train_batch)

    model.value_function = vf_saved

    return loss


def setup_tf_mixins(policy, obs_space, action_space, config):
    # Copied from PPOTFPolicy (w/o ValueNetworkMixin).
    KLCoeffMixin.__init__(policy, config)
    EntropyCoeffSchedule.__init__(
        policy, config["entropy_coeff"], config["entropy_coeff_schedule"]
    )
    LearningRateSchedule.__init__(policy, config["lr"], config["lr_schedule"])


def setup_torch_mixins(policy, obs_space, action_space, config):
    # Copied from PPOTorchPolicy  (w/o ValueNetworkMixin).
    TorchKLCoeffMixin.__init__(policy, config)
    TorchEntropyCoeffSchedule.__init__(
        policy, config["entropy_coeff"], config["entropy_coeff_schedule"]
    )
    TorchLR.__init__(policy, config["lr"], config["lr_schedule"])


def central_vf_stats(policy, train_batch, grads):
    # Report the explained variance of the central value function.
    return {
        "vf_explained_var": explained_variance(
            train_batch[Postprocessing.VALUE_TARGETS], policy._central_value_out
        )
    }


CCPPOTFPolicy = PPOTFPolicy.with_updates(
    name="CCPPOTFPolicy",
    postprocess_fn=centralized_critic_postprocessing,
    loss_fn=loss_with_central_critic,
    before_loss_init=setup_tf_mixins,
    grad_stats_fn=central_vf_stats,
    mixins=[
        LearningRateSchedule,
        EntropyCoeffSchedule,
        KLCoeffMixin,
        CentralizedValueMixin,
    ],
)


class CCPPOTorchPolicy(PPOTorchPolicy):
    def __init__(self, observation_space, action_space, config):
        super().__init__(observation_space, action_space, config)
        self.compute_central_vf = self.model.central_value_function

    @override(PPOTorchPolicy)
    def loss(self, model, dist_class, train_batch):
        return loss_with_central_critic(self, model, dist_class, train_batch)

    @override(PPOTorchPolicy)
    def postprocess_trajectory(
        self, sample_batch, other_agent_batches=None, episode=None
    ):
        return centralized_critic_postprocessing(
            self, sample_batch, other_agent_batches, episode
        )


class CCTrainer(PPOTrainer):
    @override(PPOTrainer)
    def get_default_policy_class(self, config):
        if config["framework"] == "torch":
            return CCPPOTorchPolicy
        else:
            return CCPPOTFPolicy


if __name__ == "__main__":
    ray.init()
    args = parser.parse_args()

    ModelCatalog.register_custom_model(
        "cc_model",
        TorchCentralizedCriticModel
        if args.framework == "torch"
        else CentralizedCriticModel,
    )

    config = {
        "env": TwoStepGame,
        "batch_mode": "complete_episodes",
        # Use GPUs iff `RLLIB_NUM_GPUS` env var set to > 0.
        "num_gpus": int(os.environ.get("RLLIB_NUM_GPUS", "0")),
        "num_workers": 0,
        "multiagent": {
            "policies": {
                "pol1": (
                    None,
                    Discrete(6),
                    TwoStepGame.action_space,
                    {
                        "framework": args.framework,
                    },
                ),
                "pol2": (
                    None,
                    Discrete(6),
                    TwoStepGame.action_space,
                    {
                        "framework": args.framework,
                    },
                ),
            },
            "policy_mapping_fn": (lambda aid, **kwargs: "pol1" if aid == 0 else "pol2"),
        },
        "model": {
            "custom_model": "cc_model",
        },
        "framework": args.framework,
    }

    stop = {
        "training_iteration": args.stop_iters,
        "timesteps_total": args.stop_timesteps,
        "episode_reward_mean": args.stop_reward,
    }

    results = tune.run(CCTrainer, config=config, stop=stop, verbose=1)

    if args.as_test:
        check_learning_achieved(results, args.stop_reward)