import os

import numpy as np
from stable_baselines3.common.callbacks import EvalCallback
from stable_baselines3.common.vec_env import sync_envs_normalization

from rl4lms.algorithms.common.maskable.evaluation import evaluate_policy


class MaskableEvalCallback(EvalCallback):
    """
    Callback for evaluating an agent. Supports invalid action masking.

    :param eval_env: The environment used for initialization
    :param callback_on_new_best: Callback to trigger
        when there is a new best model according to the ``mean_reward``
    :param n_eval_episodes: The number of episodes to test the agent
    :param eval_freq: Evaluate the agent every eval_freq call of the callback.
    :param log_path: Path to a folder where the evaluations (``evaluations.npz``)
        will be saved. It will be updated at each evaluation.
    :param best_model_save_path: Path to a folder where the best model
        according to performance on the eval env will be saved.
    :param deterministic: Whether the evaluation should
        use a stochastic or deterministic actions.
    :param render: Whether to render or not the environment during evaluation
    :param verbose:
    :param warn: Passed to ``evaluate_policy`` (warns if ``eval_env`` has not been
        wrapped with a Monitor wrapper)
    :param use_masking: Whether or not to use invalid action masks during evaluation
    """

    def __init__(self, *args, use_masking: bool = True, **kwargs):
        super().__init__(*args, **kwargs)
        self.use_masking = use_masking

    def _on_step(self) -> bool:
        if self.eval_freq > 0 and self.n_calls % self.eval_freq == 0:
            # Sync training and eval env if there is VecNormalize
            sync_envs_normalization(self.training_env, self.eval_env)

            # Reset success rate buffer
            self._is_success_buffer = []

            # Note that evaluate_policy() has been patched to support masking
            episode_rewards, episode_lengths = evaluate_policy(
                self.model,
                self.eval_env,
                n_eval_episodes=self.n_eval_episodes,
                render=self.render,
                deterministic=self.deterministic,
                return_episode_rewards=True,
                warn=self.warn,
                callback=self._log_success_callback,
                use_masking=self.use_masking,
            )

            if self.log_path is not None:
                self.evaluations_timesteps.append(self.num_timesteps)
                self.evaluations_results.append(episode_rewards)
                self.evaluations_length.append(episode_lengths)

                kwargs = {}
                # Save success log if present
                if len(self._is_success_buffer) > 0:
                    self.evaluations_successes.append(self._is_success_buffer)
                    kwargs = dict(successes=self.evaluations_successes)

                np.savez(
                    self.log_path,
                    timesteps=self.evaluations_timesteps,
                    results=self.evaluations_results,
                    ep_lengths=self.evaluations_length,
                    **kwargs,
                )

            mean_reward, std_reward = np.mean(
                episode_rewards), np.std(episode_rewards)
            mean_ep_length, std_ep_length = np.mean(
                episode_lengths), np.std(episode_lengths)
            self.last_mean_reward = mean_reward

            if self.verbose > 0:
                print(
                    f"Eval num_timesteps={self.num_timesteps}, " f"episode_reward={mean_reward:.2f} +/- {std_reward:.2f}")
                print(
                    f"Episode length: {mean_ep_length:.2f} +/- {std_ep_length:.2f}")
            # Add to current Logger
            self.logger.record("eval/mean_reward", float(mean_reward))
            self.logger.record("eval/mean_ep_length", mean_ep_length)

            if len(self._is_success_buffer) > 0:
                success_rate = np.mean(self._is_success_buffer)
                if self.verbose > 0:
                    print(f"Success rate: {100 * success_rate:.2f}%")
                self.logger.record("eval/success_rate", success_rate)

            # Dump log so the evaluation results are printed with the correct timestep
            self.logger.record("time/total timesteps",
                               self.num_timesteps, exclude="tensorboard")
            self.logger.dump(self.num_timesteps)

            if mean_reward > self.best_mean_reward:
                if self.verbose > 0:
                    print("New best mean reward!")
                if self.best_model_save_path is not None:
                    self.model.save(os.path.join(
                        self.best_model_save_path, "best_model"))
                self.best_mean_reward = mean_reward
                # Trigger callback if needed
                if self.callback is not None:
                    return self._on_event()

        return True
