"""
Simple Q-Learning
=================

This module provides a basic implementation of the DQN algorithm without any
optimizations.

This file defines the distributed Trainer class for the Simple Q algorithm.
See `simple_q_[tf|torch]_policy.py` for the definition of the policy loss.
"""

import logging
from typing import Optional, Type

from ray.rllib.agents.dqn.simple_q_tf_policy import SimpleQTFPolicy
from ray.rllib.agents.dqn.simple_q_torch_policy import SimpleQTorchPolicy
from ray.rllib.agents.trainer import Trainer, with_common_config
from ray.rllib.execution.concurrency_ops import Concurrently
from ray.rllib.execution.metric_ops import StandardMetricsReporting
from ray.rllib.execution.replay_ops import Replay, StoreToReplayBuffer
from ray.rllib.execution.rollout_ops import ParallelRollouts
from ray.rllib.execution.train_ops import MultiGPUTrainOneStep, TrainOneStep, \
    UpdateTargetNetwork
from ray.rllib.policy.policy import Policy
from ray.rllib.utils.annotations import override
from ray.rllib.utils.deprecation import DEPRECATED_VALUE
from ray.rllib.utils.typing import TrainerConfigDict

logger = logging.getLogger(__name__)

# yapf: disable
# __sphinx_doc_begin__
DEFAULT_CONFIG = with_common_config({
    # === Exploration Settings ===
    "exploration_config": {
        # The Exploration class to use.
        "type": "EpsilonGreedy",
        # Config for the Exploration class' constructor:
        "initial_epsilon": 1.0,
        "final_epsilon": 0.02,
        "epsilon_timesteps": 10000,  # Timesteps over which to anneal epsilon.

        # For soft_q, use:
        # "exploration_config" = {
        #   "type": "SoftQ"
        #   "temperature": [float, e.g. 1.0]
        # }
    },
    # Switch to greedy actions in evaluation workers.
    "evaluation_config": {
        "explore": False,
    },

    # Minimum env steps to optimize for per train call. This value does
    # not affect learning, only the length of iterations.
    "timesteps_per_iteration": 1000,
    # Update the target network every `target_network_update_freq` steps.
    "target_network_update_freq": 500,

    # === Replay buffer ===
    # Size of the replay buffer. Note that if async_updates is set, then
    # each worker will have a replay buffer of this size.
    "buffer_size": DEPRECATED_VALUE,
    "replay_buffer_config": {
        "type": "MultiAgentReplayBuffer",
        "capacity": 50000,
    },
    # Set this to True, if you want the contents of your buffer(s) to be
    # stored in any saved checkpoints as well.
    # Warnings will be created if:
    # - This is True AND restoring from a checkpoint that contains no buffer
    #   data.
    # - This is False AND restoring from a checkpoint that does contain
    #   buffer data.
    "store_buffer_in_checkpoints": False,
    # The number of contiguous environment steps to replay at once. This may
    # be set to greater than 1 to support recurrent models.
    "replay_sequence_length": 1,

    # === Optimization ===
    # Learning rate for adam optimizer
    "lr": 5e-4,
    # Learning rate schedule
    # In the format of [[timestep, value], [timestep, value], ...]
    # A schedule should normally start from timestep 0.
    "lr_schedule": None,
    # Adam epsilon hyper parameter
    "adam_epsilon": 1e-8,
    # If not None, clip gradients during optimization at this value
    "grad_clip": 40,
    # How many steps of the model to sample before learning starts.
    "learning_starts": 1000,
    # Update the replay buffer with this many samples at once. Note that
    # this setting applies per-worker if num_workers > 1.
    "rollout_fragment_length": 4,
    # Size of a batch sampled from replay buffer for training. Note that
    # if async_updates is set, then each worker returns gradients for a
    # batch of this size.
    "train_batch_size": 32,

    # === Parallelism ===
    # Number of workers for collecting samples with. This only makes sense
    # to increase if your environment is particularly slow to sample, or if
    # you"re using the Async or Ape-X optimizers.
    "num_workers": 0,
    # Prevent reporting frequency from going lower than this time span.
    "min_time_s_per_reporting": 1,
})
# __sphinx_doc_end__
# yapf: enable


class SimpleQTrainer(Trainer):
    @classmethod
    @override(Trainer)
    def get_default_config(cls) -> TrainerConfigDict:
        return DEFAULT_CONFIG

    @override(Trainer)
    def validate_config(self, config: TrainerConfigDict) -> None:
        """Checks and updates the config based on settings.
        """
        # Call super's validation method.
        super().validate_config(config)

        if config["exploration_config"]["type"] == "ParameterNoise":
            if config["batch_mode"] != "complete_episodes":
                logger.warning(
                    "ParameterNoise Exploration requires `batch_mode` to be "
                    "'complete_episodes'. Setting batch_mode="
                    "complete_episodes.")
                config["batch_mode"] = "complete_episodes"
            if config.get("noisy", False):
                raise ValueError(
                    "ParameterNoise Exploration and `noisy` network cannot be"
                    " used at the same time!")

        if config.get("prioritized_replay"):
            if config["multiagent"]["replay_mode"] == "lockstep":
                raise ValueError("Prioritized replay is not supported when "
                                 "replay_mode=lockstep.")
            elif config.get("replay_sequence_length", 0) > 1:
                raise ValueError("Prioritized replay is not supported when "
                                 "replay_sequence_length > 1.")
        else:
            if config.get("worker_side_prioritization"):
                raise ValueError(
                    "Worker side prioritization is not supported when "
                    "prioritized_replay=False.")

        # Multi-agent mode and multi-GPU optimizer.
        if config["multiagent"]["policies"] and \
                not config["simple_optimizer"]:
            logger.info(
                "In multi-agent mode, policies will be optimized sequentially"
                " by the multi-GPU optimizer. Consider setting "
                "`simple_optimizer=True` if this doesn't work for you.")

    @override(Trainer)
    def get_default_policy_class(
            self, config: TrainerConfigDict) -> Optional[Type[Policy]]:
        if config["framework"] == "torch":
            return SimpleQTorchPolicy
        else:
            return SimpleQTFPolicy

    @staticmethod
    @override(Trainer)
    def execution_plan(workers, config, **kwargs):
        assert "local_replay_buffer" in kwargs, (
            "GenericOffPolicy execution plan requires a local replay buffer.")

        local_replay_buffer = kwargs["local_replay_buffer"]

        rollouts = ParallelRollouts(workers, mode="bulk_sync")

        # (1) Generate rollouts and store them in our local replay buffer.
        store_op = rollouts.for_each(
            StoreToReplayBuffer(local_buffer=local_replay_buffer))

        if config["simple_optimizer"]:
            train_step_op = TrainOneStep(workers)
        else:
            train_step_op = MultiGPUTrainOneStep(
                workers=workers,
                sgd_minibatch_size=config["train_batch_size"],
                num_sgd_iter=1,
                num_gpus=config["num_gpus"],
                _fake_gpus=config["_fake_gpus"])

        # (2) Read and train on experiences from the replay buffer.
        replay_op = Replay(local_buffer=local_replay_buffer) \
            .for_each(train_step_op) \
            .for_each(UpdateTargetNetwork(
                workers, config["target_network_update_freq"]))

        # Alternate deterministically between (1) and (2).
        train_op = Concurrently(
            [store_op, replay_op], mode="round_robin", output_indexes=[1])

        return StandardMetricsReporting(train_op, workers, config)