from typing import Any, Dict, List, Optional, Tuple, Union

import numpy as np

from tianshou.data import Batch, ReplayBuffer
from tianshou.data.batch import BatchProtocol
from tianshou.data.types import RolloutBatchProtocol
from tianshou.policy import BasePolicy

try:
    from tianshou.env.pettingzoo_env import PettingZooEnv
except ImportError:
    PettingZooEnv = None  # type: ignore


class MultiAgentPolicyManager(BasePolicy):
    """Multi-agent policy manager for MARL.

    This multi-agent policy manager accepts a list of
    :class:`~tianshou.policy.BasePolicy`. It dispatches the batch data to each
    of these policies when the "forward" is called. The same as "process_fn"
    and "learn": it splits the data and feeds them to each policy. A figure in
    :ref:`marl_example` can help you better understand this procedure.
    """

    def __init__(
        self, policies: List[BasePolicy], env: PettingZooEnv, **kwargs: Any
    ) -> None:
        super().__init__(action_space=env.action_space, **kwargs)
        assert (
            len(policies) == len(env.agents)
        ), "One policy must be assigned for each agent."

        self.agent_idx = env.agent_idx
        for i, policy in enumerate(policies):
            # agent_id 0 is reserved for the environment proxy
            # (this MultiAgentPolicyManager)
            policy.set_agent_id(env.agents[i])

        self.policies = dict(zip(env.agents, policies))

    def replace_policy(self, policy: BasePolicy, agent_id: int) -> None:
        """Replace the "agent_id"th policy in this manager."""
        policy.set_agent_id(agent_id)
        self.policies[agent_id] = policy

    # TODO: violates Liskov substitution principle
    def process_fn(  # type: ignore
        self, batch: RolloutBatchProtocol, buffer: ReplayBuffer, indice: np.ndarray
    ) -> BatchProtocol:
        """Dispatch batch data from obs.agent_id to every policy's process_fn.

        Save original multi-dimensional rew in "save_rew", set rew to the
        reward of each agent during their "process_fn", and restore the
        original reward afterwards.
        """
        results = {}
        assert isinstance(batch.obs, BatchProtocol), \
            (f"here only observations of type Batch are permitted, "
             f"but got {type(batch.obs)}")
        # reward can be empty Batch (after initial reset) or nparray.
        has_rew = isinstance(buffer.rew, np.ndarray)
        if has_rew:  # save the original reward in save_rew
            # Since we do not override buffer.__setattr__, here we use _meta to
            # change buffer.rew, otherwise buffer.rew = Batch() has no effect.
            save_rew, buffer._meta.rew = buffer.rew, Batch()  # type: ignore
        for agent, policy in self.policies.items():
            agent_index = np.nonzero(batch.obs.agent_id == agent)[0]
            if len(agent_index) == 0:
                results[agent] = Batch()
                continue
            tmp_batch, tmp_indice = batch[agent_index], indice[agent_index]
            if has_rew:
                tmp_batch.rew = tmp_batch.rew[:, self.agent_idx[agent]]
                buffer._meta.rew = save_rew[:, self.agent_idx[agent]]
            if not hasattr(tmp_batch.obs, "mask"):
                if hasattr(tmp_batch.obs, 'obs'):
                    tmp_batch.obs = tmp_batch.obs.obs
                if hasattr(tmp_batch.obs_next, 'obs'):
                    tmp_batch.obs_next = tmp_batch.obs_next.obs
            results[agent] = policy.process_fn(tmp_batch, buffer, tmp_indice)
        if has_rew:  # restore from save_rew
            buffer._meta.rew = save_rew
        return Batch(results)

    def exploration_noise(
        self, act: Union[np.ndarray, BatchProtocol], batch: RolloutBatchProtocol
    ) -> Union[np.ndarray, BatchProtocol]:
        """Add exploration noise from sub-policy onto act."""
        assert isinstance(batch.obs, BatchProtocol), \
            (f"here only observations of type Batch are permitted, "
             f"but got {type(batch.obs)}")
        for agent_id, policy in self.policies.items():
            agent_index = np.nonzero(batch.obs.agent_id == agent_id)[0]
            if len(agent_index) == 0:
                continue
            act[agent_index] = policy.exploration_noise(
                act[agent_index], batch[agent_index]
            )
        return act

    def forward(  # type: ignore
        self,
        batch: Batch,
        state: Optional[Union[dict, Batch]] = None,
        **kwargs: Any,
    ) -> Batch:
        """Dispatch batch data from obs.agent_id to every policy's forward.

        :param state: if None, it means all agents have no state. If not
            None, it should contain keys of "agent_1", "agent_2", ...

        :return: a Batch with the following contents:

        ::

            {
                "act": actions corresponding to the input
                "state": {
                    "agent_1": output state of agent_1's policy for the state
                    "agent_2": xxx
                    ...
                    "agent_n": xxx}
                "out": {
                    "agent_1": output of agent_1's policy for the input
                    "agent_2": xxx
                    ...
                    "agent_n": xxx}
            }
        """
        results: List[Tuple[bool, np.ndarray, Batch, Union[np.ndarray, Batch],
                            Batch]] = []
        for agent_id, policy in self.policies.items():
            # This part of code is difficult to understand.
            # Let's follow an example with two agents
            # batch.obs.agent_id is [1, 2, 1, 2, 1, 2] (with batch_size == 6)
            # each agent plays for three transitions
            # agent_index for agent 1 is [0, 2, 4]
            # agent_index for agent 2 is [1, 3, 5]
            # we separate the transition of each agent according to agent_id
            agent_index = np.nonzero(batch.obs.agent_id == agent_id)[0]
            if len(agent_index) == 0:
                # (has_data, agent_index, out, act, state)
                results.append((False, np.array([-1]), Batch(), Batch(), Batch()))
                continue
            tmp_batch = batch[agent_index]
            if isinstance(tmp_batch.rew, np.ndarray):
                # reward can be empty Batch (after initial reset) or nparray.
                tmp_batch.rew = tmp_batch.rew[:, self.agent_idx[agent_id]]
            if not hasattr(tmp_batch.obs, "mask"):
                if hasattr(tmp_batch.obs, 'obs'):
                    tmp_batch.obs = tmp_batch.obs.obs
                if hasattr(tmp_batch.obs_next, 'obs'):
                    tmp_batch.obs_next = tmp_batch.obs_next.obs
            out = policy(
                batch=tmp_batch,
                state=None if state is None else state[agent_id],
                **kwargs
            )
            act = out.act
            each_state = out.state \
                if (hasattr(out, "state") and out.state is not None) \
                else Batch()
            results.append((True, agent_index, out, act, each_state))
        holder: Batch = Batch.cat(
            [
                {
                    "act": act
                } for (has_data, agent_index, out, act, each_state) in results
                if has_data
            ]
        )
        state_dict, out_dict = {}, {}
        for (agent_id, _), (has_data, agent_index, out, act,
                            state) in zip(self.policies.items(), results):
            if has_data:
                holder.act[agent_index] = act
            state_dict[agent_id] = state
            out_dict[agent_id] = out
        holder["out"] = out_dict
        holder["state"] = state_dict
        return holder

    def learn(self, batch: RolloutBatchProtocol, *args: Any,
              **kwargs: Any) -> Dict[str, Union[float, List[float]]]:
        """Dispatch the data to all policies for learning.

        :return: a dict with the following contents:

        ::

            {
                "agent_1/item1": item 1 of agent_1's policy.learn output
                "agent_1/item2": item 2 of agent_1's policy.learn output
                "agent_2/xxx": xxx
                ...
                "agent_n/xxx": xxx
            }
        """
        results = {}
        for agent_id, policy in self.policies.items():
            data = batch[agent_id]
            if not data.is_empty():
                out = policy.learn(batch=data, **kwargs)
                for k, v in out.items():
                    results[agent_id + "/" + k] = v
        return results