# Copyright 2019 DeepMind Technologies Limited
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

"""Neural Fictitious Self-Play (NFSP) agent implemented in Jax.

The code is around 4x slower than the TF implementation at the moment. Future
PRs improving the runtime are welcome.

See the paper https://arxiv.org/abs/1603.01121 for more details.
"""

import collections
import contextlib
import enum
import os

import haiku as hk
import jax
import jax.numpy as jnp
import numpy as np
import optax

from open_spiel.python import rl_agent
from open_spiel.python.jax import dqn
from open_spiel.python.utils.reservoir_buffer import ReservoirBuffer

Transition = collections.namedtuple(
    "Transition", "info_state action_probs legal_actions_mask")

MODE = enum.Enum("mode", "best_response average_policy")


class NFSP(rl_agent.AbstractAgent):
  """NFSP Agent implementation in JAX.

  See open_spiel/python/examples/kuhn_nfsp.py for an usage example.
  """

  def __init__(self,
               player_id,
               state_representation_size,
               num_actions,
               hidden_layers_sizes,
               reservoir_buffer_capacity,
               anticipatory_param,
               batch_size=128,
               rl_learning_rate=0.01,
               sl_learning_rate=0.01,
               min_buffer_size_to_learn=1000,
               learn_every=64,
               optimizer_str="sgd",
               **kwargs):
    """Initialize the `NFSP` agent."""
    self.player_id = player_id
    self._num_actions = num_actions
    self._layer_sizes = hidden_layers_sizes
    self._batch_size = batch_size
    self._learn_every = learn_every
    self._anticipatory_param = anticipatory_param
    self._min_buffer_size_to_learn = min_buffer_size_to_learn

    self._reservoir_buffer = ReservoirBuffer(reservoir_buffer_capacity)
    self._prev_timestep = None
    self._prev_action = None

    # Step counter to keep track of learning.
    self._step_counter = 0

    # Inner RL agent
    kwargs.update({
        "batch_size": batch_size,
        "learning_rate": rl_learning_rate,
        "learn_every": learn_every,
        "min_buffer_size_to_learn": min_buffer_size_to_learn,
        "optimizer_str": optimizer_str,
    })
    self._rl_agent = dqn.DQN(player_id, state_representation_size,
                             num_actions, hidden_layers_sizes, **kwargs)

    # Keep track of the last training loss achieved in an update step.
    self._last_rl_loss_value = lambda: self._rl_agent.loss
    self._last_sl_loss_value = None

    # Average policy network.
    def network(x):
      mlp = hk.nets.MLP(self._layer_sizes + [num_actions])
      return mlp(x)

    self.hk_avg_network = hk.without_apply_rng(hk.transform(network))

    def avg_network_policy(param, info_state):
      action_values = self.hk_avg_network.apply(param, info_state)
      action_probs = jax.nn.softmax(action_values, axis=1)
      return action_values, action_probs

    self._avg_network_policy = jax.jit(avg_network_policy)

    rng = jax.random.PRNGKey(42)
    x = jnp.ones([1, state_representation_size])
    self.params_avg_network = self.hk_avg_network.init(rng, x)
    self.params_avg_network = jax.device_put(self.params_avg_network)

    self._savers = [
        ("q_network", self._rl_agent.params_q_network),
        ("avg_network", self.params_avg_network)
    ]

    if optimizer_str == "adam":
      opt_init, opt_update = optax.chain(
          optax.scale_by_adam(b1=0.9, b2=0.999, eps=1e-8),
          optax.scale(sl_learning_rate))
    elif optimizer_str == "sgd":
      opt_init, opt_update = optax.sgd(sl_learning_rate)
    else:
      raise ValueError("Not implemented. Choose from ['adam', 'sgd'].")
    self._opt_update_fn = self._get_update_func(opt_update)
    self._opt_state = opt_init(self.params_avg_network)
    self._loss_and_grad = jax.value_and_grad(self._loss_avg, has_aux=False)

    self._sample_episode_policy()
    self._jit_update = jax.jit(self.get_update())

  def _get_update_func(self, opt_update):

    def update(params, opt_state, gradient):
      """Learning rule (stochastic gradient descent)."""
      updates, opt_state = opt_update(gradient, opt_state)
      new_params = optax.apply_updates(params, updates)
      return new_params, opt_state

    return update

  def get_step_counter(self):
    return self._step_counter

  @contextlib.contextmanager
  def temp_mode_as(self, mode):
    """Context manager to temporarily overwrite the mode."""
    previous_mode = self._mode
    self._mode = mode
    yield
    self._mode = previous_mode

  def _sample_episode_policy(self):
    if np.random.rand() < self._anticipatory_param:
      self._mode = MODE.best_response
    else:
      self._mode = MODE.average_policy

  def _act(self, info_state, legal_actions):
    info_state = np.reshape(info_state, [1, -1])
    action_values, action_probs = self._avg_network_policy(
        self.params_avg_network, info_state
        )

    self._last_action_values = action_values[0]
    # Remove illegal actions, normalize probs
    probs = np.zeros(self._num_actions)
    action_probs = np.asarray(action_probs)
    probs[legal_actions] = action_probs[0][legal_actions]
    probs /= sum(probs)
    action = np.random.choice(len(probs), p=probs)
    return action, probs

  @property
  def mode(self):
    return self._mode

  @property
  def loss(self):
    return (self._last_sl_loss_value, self._last_rl_loss_value())

  def step(self, time_step, is_evaluation=False):
    """Returns the action to be taken and updates the Q-networks if needed.

    Args:
      time_step: an instance of rl_environment.TimeStep.
      is_evaluation: bool, whether this is a training or evaluation call.

    Returns:
      A `rl_agent.StepOutput` containing the action probs and chosen action.
    """
    if self._mode == MODE.best_response:
      agent_output = self._rl_agent.step(time_step, is_evaluation)
      if not is_evaluation and not time_step.last():
        self._add_transition(time_step, agent_output)

    elif self._mode == MODE.average_policy:
      # Act step: don't act at terminal info states.
      if not time_step.last():
        info_state = time_step.observations["info_state"][self.player_id]
        legal_actions = time_step.observations["legal_actions"][self.player_id]
        action, probs = self._act(info_state, legal_actions)
        agent_output = rl_agent.StepOutput(action=action, probs=probs)

      if self._prev_timestep and not is_evaluation:
        self._rl_agent.add_transition(self._prev_timestep, self._prev_action,
                                      time_step)
    else:
      raise ValueError("Invalid mode ({})".format(self._mode))

    if not is_evaluation:
      self._step_counter += 1

      if self._step_counter % self._learn_every == 0:
        self._last_sl_loss_value = self._learn()
        # If learn step not triggered by rl policy, learn.
        if self._mode == MODE.average_policy:
          self._rl_agent.learn()

      # Prepare for the next episode.
      if time_step.last():
        self._sample_episode_policy()
        self._prev_timestep = None
        self._prev_action = None
        return
      else:
        self._prev_timestep = time_step
        self._prev_action = agent_output.action
    return agent_output

  def _add_transition(self, time_step, agent_output):
    """Adds the new transition using `time_step` to the reservoir buffer.

    Transitions are in the form (time_step, agent_output.probs, legal_mask).

    Args:
      time_step: an instance of rl_environment.TimeStep.
      agent_output: an instance of rl_agent.StepOutput.
    """
    legal_actions = time_step.observations["legal_actions"][self.player_id]
    legal_actions_mask = np.zeros(self._num_actions)
    legal_actions_mask[legal_actions] = 1.0
    transition = Transition(
        info_state=(time_step.observations["info_state"][self.player_id][:]),
        action_probs=agent_output.probs,
        legal_actions_mask=legal_actions_mask)
    self._reservoir_buffer.add(transition)

  def _loss_avg(self, param_avg, info_states, action_probs):
    avg_logit = self.hk_avg_network.apply(param_avg, info_states)
    loss_value = -jnp.sum(
        action_probs * jax.nn.log_softmax(avg_logit)) / avg_logit.shape[0]
    return loss_value

  def get_update(self):
    def update(param_avg, opt_state_avg, info_states, action_probs):
      loss_val, grad_val = self._loss_and_grad(param_avg, info_states,
                                               action_probs)
      new_param_avg, new_opt_state_avg = self._opt_update_fn(
          param_avg, opt_state_avg, grad_val)
      return new_param_avg, new_opt_state_avg, loss_val
    return update

  def _learn(self):
    """Compute the loss on sampled transitions and perform a avg-network update.

    If there are not enough elements in the buffer, no loss is computed and
    `None` is returned instead.

    Returns:
      The average loss obtained on this batch of transitions or `None`.
    """
    if (len(self._reservoir_buffer) < self._batch_size or
        len(self._reservoir_buffer) < self._min_buffer_size_to_learn):
      return None

    transitions = self._reservoir_buffer.sample(self._batch_size)
    info_states = np.asarray([t.info_state for t in transitions])
    action_probs = np.asarray([t.action_probs for t in transitions])

    self.params_avg_network, self._opt_state, loss_val_avg = self._jit_update(
        self.params_avg_network, self._opt_state, info_states, action_probs)
    return loss_val_avg

  def _full_checkpoint_name(self, checkpoint_dir, name):
    checkpoint_filename = "_".join([name, "pid" + str(self.player_id)])
    return os.path.join(checkpoint_dir, checkpoint_filename)

  def _latest_checkpoint_filename(self, name):
    checkpoint_filename = "_".join([name, "pid" + str(self.player_id)])
    return checkpoint_filename + "_latest"

  def save(self, checkpoint_dir):
    """Saves the average policy network and the inner RL agent's q-network.

    Note that this does not save the experience replay buffers and should
    only be used to restore the agent's policy, not resume training.

    Args:
      checkpoint_dir: directory where checkpoints will be saved.
    """
    raise NotImplementedError

  def has_checkpoint(self, checkpoint_dir):
    for name, _ in self._savers:
      path = self._full_checkpoint_name(checkpoint_dir, name)
      if os.path.exists(path):
        return True
    return False

  def restore(self, checkpoint_dir):
    """Restores the average policy network and the inner RL agent's q-network.

    Note that this does not restore the experience replay buffers and should
    only be used to restore the agent's policy, not resume training.

    Args:
      checkpoint_dir: directory from which checkpoints will be restored.
    """
    raise NotImplementedError
