import logging

import random
import numpy as np

from ray.rllib.agents import with_common_config
from ray.rllib.agents.dreamer.dreamer_torch_policy import DreamerTorchPolicy
from ray.rllib.agents.trainer_template import build_trainer
from ray.rllib.execution.common import STEPS_SAMPLED_COUNTER, \
    LEARNER_INFO, _get_shared_metrics
from ray.rllib.policy.sample_batch import DEFAULT_POLICY_ID, SampleBatch
from ray.rllib.evaluation.metrics import collect_metrics
from ray.rllib.agents.dreamer.dreamer_model import DreamerModel
from ray.rllib.execution.rollout_ops import ParallelRollouts
from ray.rllib.utils.typing import SampleBatchType

logger = logging.getLogger(__name__)

# yapf: disable
# __sphinx_doc_begin__
DEFAULT_CONFIG = with_common_config({
    # PlaNET Model LR
    "td_model_lr": 6e-4,
    # Actor LR
    "actor_lr": 8e-5,
    # Critic LR
    "critic_lr": 8e-5,
    # Grad Clipping
    "grad_clip": 100.0,
    # Discount
    "discount": 0.99,
    # Lambda
    "lambda": 0.95,
    # Clipping is done inherently via policy tanh.
    "clip_actions": False,
    # Training iterations per data collection from real env
    "dreamer_train_iters": 100,
    # Horizon for Enviornment (1000 for Mujoco/DMC)
    "horizon": 1000,
    # Number of episodes to sample for Loss Calculation
    "batch_size": 50,
    # Length of each episode to sample for Loss Calculation
    "batch_length": 50,
    # Imagination Horizon for Training Actor and Critic
    "imagine_horizon": 15,
    # Free Nats
    "free_nats": 3.0,
    # KL Coeff for the Model Loss
    "kl_coeff": 1.0,
    # Distributed Dreamer not implemented yet
    "num_workers": 0,
    # Prefill Timesteps
    "prefill_timesteps": 5000,
    # This should be kept at 1 to preserve sample efficiency
    "num_envs_per_worker": 1,
    # Exploration Gaussian
    "explore_noise": 0.3,
    # Batch mode
    "batch_mode": "complete_episodes",
    # Custom Model
    "dreamer_model": {
        "custom_model": DreamerModel,
        # RSSM/PlaNET parameters
        "deter_size": 200,
        "stoch_size": 30,
        # CNN Decoder Encoder
        "depth_size": 32,
        # General Network Parameters
        "hidden_size": 400,
        # Action STD
        "action_init_std": 5.0,
    },

    "env_config": {
        # Repeats action send by policy for frame_skip times in env
        "frame_skip": 2,
    }
})
# __sphinx_doc_end__
# yapf: enable


class EpisodicBuffer(object):
    def __init__(self, max_length: int = 1000, length: int = 50):
        """Data structure that stores episodes and samples chunks
        of size length from episodes

        Args:
            max_length: Maximum episodes it can store
            length: Episode chunking lengh in sample()
        """

        # Stores all episodes into a list: List[SampleBatchType]
        self.episodes = []
        self.max_length = max_length
        self.timesteps = 0
        self.length = length

    def add(self, batch: SampleBatchType):
        """Splits a SampleBatch into episodes and adds episodes
        to the episode buffer

        Args:
            batch: SampleBatch to be added
        """

        self.timesteps += batch.count
        episodes = batch.split_by_episode()

        for i, e in enumerate(episodes):
            episodes[i] = self.preprocess_episode(e)
        self.episodes.extend(episodes)

        if len(self.episodes) > self.max_length:
            delta = len(self.episodes) - self.max_length
            # Drop oldest episodes
            self.episodes = self.episodes[delta:]

    def preprocess_episode(self, episode: SampleBatchType):
        """Batch format should be in the form of (s_t, a_(t-1), r_(t-1))
        When t=0, the resetted obs is paired with action and reward of 0.

        Args:
            episode: SampleBatch representing an episode
        """
        obs = episode["obs"]
        new_obs = episode["new_obs"]
        action = episode["actions"]
        reward = episode["rewards"]

        act_shape = action.shape
        act_reset = np.array([0.0] * act_shape[-1])[None]
        rew_reset = np.array(0.0)[None]
        obs_end = np.array(new_obs[act_shape[0] - 1])[None]

        batch_obs = np.concatenate([obs, obs_end], axis=0)
        batch_action = np.concatenate([act_reset, action], axis=0)
        batch_rew = np.concatenate([rew_reset, reward], axis=0)

        new_batch = {
            "obs": batch_obs,
            "rewards": batch_rew,
            "actions": batch_action
        }
        return SampleBatch(new_batch)

    def sample(self, batch_size: int):
        """Samples [batch_size, length] from the list of episodes

        Args:
            batch_size: batch_size to be sampled
        """
        episodes_buffer = []
        while len(episodes_buffer) < batch_size:
            rand_index = random.randint(0, len(self.episodes) - 1)
            episode = self.episodes[rand_index]
            if episode.count < self.length:
                continue
            available = episode.count - self.length
            index = int(random.randint(0, available))
            episodes_buffer.append(episode.slice(index, index + self.length))

        batch = {}
        for k in episodes_buffer[0].keys():
            batch[k] = np.stack([e[k] for e in episodes_buffer], axis=0)

        return SampleBatch(batch)


def total_sampled_timesteps(worker):
    return worker.policy_map[DEFAULT_POLICY_ID].global_timestep


class DreamerIteration:
    def __init__(self, worker, episode_buffer, dreamer_train_iters, batch_size,
                 act_repeat):
        self.worker = worker
        self.episode_buffer = episode_buffer
        self.dreamer_train_iters = dreamer_train_iters
        self.repeat = act_repeat
        self.batch_size = batch_size

    def __call__(self, samples):

        # Dreamer Training Loop
        for n in range(self.dreamer_train_iters):
            print(n)
            batch = self.episode_buffer.sample(self.batch_size)
            if n == self.dreamer_train_iters - 1:
                batch["log_gif"] = True
            fetches = self.worker.learn_on_batch(batch)

        # Custom Logging
        policy_fetches = self.policy_stats(fetches)
        if "log_gif" in policy_fetches:
            gif = policy_fetches["log_gif"]
            policy_fetches["log_gif"] = self.postprocess_gif(gif)

        # Metrics Calculation
        metrics = _get_shared_metrics()
        metrics.info[LEARNER_INFO] = fetches
        metrics.counters[STEPS_SAMPLED_COUNTER] = self.episode_buffer.timesteps
        metrics.counters[STEPS_SAMPLED_COUNTER] *= self.repeat
        res = collect_metrics(local_worker=self.worker)
        res["info"] = metrics.info
        res["info"].update(metrics.counters)
        res["timesteps_total"] = metrics.counters[STEPS_SAMPLED_COUNTER]

        self.episode_buffer.add(samples)
        return res

    def postprocess_gif(self, gif: np.ndarray):
        gif = np.clip(255 * gif, 0, 255).astype(np.uint8)
        B, T, C, H, W = gif.shape
        frames = gif.transpose((1, 2, 3, 0, 4)).reshape((1, T, C, H, B * W))
        return frames

    def policy_stats(self, fetches):
        return fetches[DEFAULT_POLICY_ID]["learner_stats"]


def execution_plan(workers, config):
    # Special Replay Buffer for Dreamer agent
    episode_buffer = EpisodicBuffer(length=config["batch_length"])

    local_worker = workers.local_worker()

    # Prefill episode buffer with initial exploration (uniform sampling)
    while total_sampled_timesteps(local_worker) < config["prefill_timesteps"]:
        samples = local_worker.sample()
        episode_buffer.add(samples)

    batch_size = config["batch_size"]
    dreamer_train_iters = config["dreamer_train_iters"]
    act_repeat = config["action_repeat"]

    rollouts = ParallelRollouts(workers)
    rollouts = rollouts.for_each(
        DreamerIteration(local_worker, episode_buffer, dreamer_train_iters,
                         batch_size, act_repeat))
    return rollouts


def get_policy_class(config):
    return DreamerTorchPolicy


def validate_config(config):
    config["action_repeat"] = config["env_config"]["frame_skip"]
    if config["framework"] != "torch":
        raise ValueError("Dreamer not supported in Tensorflow yet!")
    if config["batch_mode"] != "complete_episodes":
        raise ValueError("truncate_episodes not supported")
    if config["num_workers"] != 0:
        raise ValueError("Distributed Dreamer not supported yet!")
    if config["clip_actions"]:
        raise ValueError("Clipping is done inherently via policy tanh!")
    if config["action_repeat"] > 1:
        config["horizon"] = config["horizon"] / config["action_repeat"]


DREAMERTrainer = build_trainer(
    name="Dreamer",
    default_config=DEFAULT_CONFIG,
    default_policy=DreamerTorchPolicy,
    get_policy_class=get_policy_class,
    execution_plan=execution_plan,
    validate_config=validate_config)
