from typing import Type

from ray.rllib.agents.trainer import with_common_config
from ray.rllib.agents.dqn.simple_q import SimpleQTrainer
from ray.rllib.agents.qmix.qmix_policy import QMixTorchPolicy
from ray.rllib.evaluation.worker_set import WorkerSet
from ray.rllib.execution.concurrency_ops import Concurrently
from ray.rllib.execution.metric_ops import StandardMetricsReporting
from ray.rllib.execution.replay_ops import SimpleReplayBuffer, Replay, \
    StoreToReplayBuffer
from ray.rllib.execution.rollout_ops import ParallelRollouts, ConcatBatches
from ray.rllib.execution.train_ops import TrainOneStep, UpdateTargetNetwork
from ray.rllib.policy.policy import Policy
from ray.rllib.utils.annotations import override
from ray.rllib.utils.typing import TrainerConfigDict
from ray.util.iter import LocalIterator

# yapf: disable
# __sphinx_doc_begin__
DEFAULT_CONFIG = with_common_config({
    # === QMix ===
    # Mixing network. Either "qmix", "vdn", or None
    "mixer": "qmix",
    # Size of the mixing network embedding
    "mixing_embed_dim": 32,
    # Whether to use Double_Q learning
    "double_q": True,
    # Optimize over complete episodes by default.
    "batch_mode": "complete_episodes",

    # === Exploration Settings ===
    "exploration_config": {
        # The Exploration class to use.
        "type": "EpsilonGreedy",
        # Config for the Exploration class' constructor:
        "initial_epsilon": 1.0,
        "final_epsilon": 0.01,
        # Timesteps over which to anneal epsilon.
        "epsilon_timesteps": 40000,

        # For soft_q, use:
        # "exploration_config" = {
        #   "type": "SoftQ"
        #   "temperature": [float, e.g. 1.0]
        # }
    },

    # === Evaluation ===
    # Evaluate with epsilon=0 every `evaluation_interval` training iterations.
    # The evaluation stats will be reported under the "evaluation" metric key.
    # Note that evaluation is currently not parallelized, and that for Ape-X
    # metrics are already only reported for the lowest epsilon workers.
    "evaluation_interval": None,
    # Number of episodes to run per evaluation period.
    "evaluation_duration": 10,
    # Switch to greedy actions in evaluation workers.
    "evaluation_config": {
        "explore": False,
    },

    # Number of env steps to optimize for before returning
    "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 in batches (not timesteps!).
    "buffer_size": 1000,
    # === Optimization ===
    # Learning rate for RMSProp optimizer
    "lr": 0.0005,
    # RMSProp alpha
    "optim_alpha": 0.99,
    # RMSProp epsilon
    "optim_eps": 0.00001,
    # If not None, clip gradients during optimization at this value
    "grad_norm_clipping": 10,
    # 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 batched 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,
    # Whether to compute priorities on workers.
    "worker_side_prioritization": False,
    # Prevent reporting frequency from going lower than this time span.
    "min_time_s_per_reporting": 1,

    # === Model ===
    "model": {
        "lstm_cell_size": 64,
        "max_seq_len": 999999,
    },
    # Only torch supported so far.
    "framework": "torch",
})
# __sphinx_doc_end__
# yapf: enable


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

    @override(SimpleQTrainer)
    def validate_config(self, config: TrainerConfigDict) -> None:
        # Call super's validation method.
        super().validate_config(config)

        if config["framework"] != "torch":
            raise ValueError(
                "Only `framework=torch` supported so far for QMixTrainer!")

    @override(SimpleQTrainer)
    def get_default_policy_class(self,
                                 config: TrainerConfigDict) -> Type[Policy]:
        return QMixTorchPolicy

    @staticmethod
    @override(SimpleQTrainer)
    def execution_plan(workers: WorkerSet, config: TrainerConfigDict,
                       **kwargs) -> LocalIterator[dict]:
        assert len(kwargs) == 0, (
            "QMIX execution_plan does NOT take any additional parameters")

        rollouts = ParallelRollouts(workers, mode="bulk_sync")
        replay_buffer = SimpleReplayBuffer(config["buffer_size"])

        store_op = rollouts \
            .for_each(StoreToReplayBuffer(local_buffer=replay_buffer))

        train_op = Replay(local_buffer=replay_buffer) \
            .combine(
            ConcatBatches(
                min_batch_size=config["train_batch_size"],
                count_steps_by=config["multiagent"]["count_steps_by"]
            )) \
            .for_each(TrainOneStep(workers)) \
            .for_each(UpdateTargetNetwork(
                workers, config["target_network_update_freq"]))

        merged_op = Concurrently(
            [store_op, train_op], mode="round_robin", output_indexes=[1])

        return StandardMetricsReporting(merged_op, workers, config)