"""
Model-free online RL with DIffusion POlicy (DIPO)

Applies action gradient to perturb actions towards maximizer of Q-function.

a_t <- a_t + \eta * \grad_a Q(s, a)

Do not support pixel input right now.

"""

import os
import pickle
import numpy as np
import torch
import logging
import wandb

log = logging.getLogger(__name__)
from util.timer import Timer
from collections import deque
from agent.finetune.train_agent import TrainAgent
from util.scheduler import CosineAnnealingWarmupRestarts


class TrainDIPODiffusionAgent(TrainAgent):

    def __init__(self, cfg):
        super().__init__(cfg)

        # note the discount factor gamma here is applied to reward every act_steps, instead of every env step
        self.gamma = cfg.train.gamma

        # Wwarm up period for critic before actor updates
        self.n_critic_warmup_itr = cfg.train.n_critic_warmup_itr

        # Optimizer
        self.actor_optimizer = torch.optim.AdamW(
            self.model.actor.parameters(),
            lr=cfg.train.actor_lr,
            weight_decay=cfg.train.actor_weight_decay,
        )
        # use cosine scheduler with linear warmup
        self.actor_lr_scheduler = CosineAnnealingWarmupRestarts(
            self.actor_optimizer,
            first_cycle_steps=cfg.train.actor_lr_scheduler.first_cycle_steps,
            cycle_mult=1.0,
            max_lr=cfg.train.actor_lr,
            min_lr=cfg.train.actor_lr_scheduler.min_lr,
            warmup_steps=cfg.train.actor_lr_scheduler.warmup_steps,
            gamma=1.0,
        )
        self.critic_optimizer = torch.optim.AdamW(
            self.model.critic.parameters(),
            lr=cfg.train.critic_lr,
            weight_decay=cfg.train.critic_weight_decay,
        )
        self.critic_lr_scheduler = CosineAnnealingWarmupRestarts(
            self.critic_optimizer,
            first_cycle_steps=cfg.train.critic_lr_scheduler.first_cycle_steps,
            cycle_mult=1.0,
            max_lr=cfg.train.critic_lr,
            min_lr=cfg.train.critic_lr_scheduler.min_lr,
            warmup_steps=cfg.train.critic_lr_scheduler.warmup_steps,
            gamma=1.0,
        )

        # Buffer size
        self.buffer_size = cfg.train.buffer_size

        # Perturbation scale
        self.eta = cfg.train.eta

        # Updates
        self.replay_ratio = cfg.train.replay_ratio

        # Scaling reward
        self.scale_reward_factor = cfg.train.scale_reward_factor

        # Apply action gradient many steps
        self.action_gradient_steps = cfg.train.action_gradient_steps

    def run(self):

        # make a FIFO replay buffer for obs, action, and reward
        obs_buffer = deque(maxlen=self.buffer_size)
        next_obs_buffer = deque(maxlen=self.buffer_size)
        action_buffer = deque(maxlen=self.buffer_size)
        reward_buffer = deque(maxlen=self.buffer_size)
        done_buffer = deque(maxlen=self.buffer_size)
        first_buffer = deque(maxlen=self.buffer_size)

        # Start training loop
        timer = Timer()
        run_results = []
        last_itr_eval = False
        done_venv = np.zeros((1, self.n_envs))
        while self.itr < self.n_train_itr:

            # Prepare video paths for each envs --- only applies for the first set of episodes if allowing reset within iteration and each iteration has multiple episodes from one env
            options_venv = [{} for _ in range(self.n_envs)]
            if self.itr % self.render_freq == 0 and self.render_video:
                for env_ind in range(self.n_render):
                    options_venv[env_ind]["video_path"] = os.path.join(
                        self.render_dir, f"itr-{self.itr}_trial-{env_ind}.mp4"
                    )

            # Define train or eval - all envs restart
            eval_mode = self.itr % self.val_freq == 0 and not self.force_train
            self.model.eval() if eval_mode else self.model.train()
            last_itr_eval = eval_mode

            # Reset env before iteration starts (1) if specified, (2) at eval mode, or (3) right after eval mode
            firsts_trajs = np.zeros((self.n_steps + 1, self.n_envs))
            if self.reset_at_iteration or eval_mode or last_itr_eval:
                prev_obs_venv = self.reset_env_all(options_venv=options_venv)
                firsts_trajs[0] = 1
            else:
                firsts_trajs[0] = (
                    done_venv  # if done at the end of last iteration, then the envs are just reset
                )
            reward_trajs = np.empty((0, self.n_envs))

            # Collect a set of trajectories from env
            for step in range(self.n_steps):
                if step % 10 == 0:
                    print(f"Processed step {step} of {self.n_steps}")

                # Select action
                with torch.no_grad():
                    cond = {
                        "state": torch.from_numpy(prev_obs_venv["state"])
                        .float()
                        .to(self.device)
                    }
                    samples = (
                        self.model(
                            cond=cond,
                            deterministic=eval_mode,
                        )
                        .cpu()
                        .numpy()
                    )  # n_env x horizon x act
                action_venv = samples[:, : self.act_steps]

                # Apply multi-step action
                obs_venv, reward_venv, done_venv, info_venv = self.venv.step(
                    action_venv
                )
                reward_trajs = np.vstack((reward_trajs, reward_venv[None]))

                # add to buffer
                for i in range(self.n_envs):
                    obs_buffer.append(prev_obs_venv["state"][i])
                    next_obs_buffer.append(obs_venv["state"][i])
                    action_buffer.append(action_venv[i])
                    reward_buffer.append(reward_venv[i] * self.scale_reward_factor)
                    done_buffer.append(done_venv[i])
                first_buffer.append(firsts_trajs[step])

                firsts_trajs[step + 1] = done_venv
                prev_obs_venv = obs_venv

            # Summarize episode reward --- this needs to be handled differently depending on whether the environment is reset after each iteration. Only count episodes that finish within the iteration.
            episodes_start_end = []
            for env_ind in range(self.n_envs):
                env_steps = np.where(firsts_trajs[:, env_ind] == 1)[0]
                for i in range(len(env_steps) - 1):
                    start = env_steps[i]
                    end = env_steps[i + 1]
                    if end - start > 1:
                        episodes_start_end.append((env_ind, start, end - 1))
            if len(episodes_start_end) > 0:
                reward_trajs_split = [
                    reward_trajs[start : end + 1, env_ind]
                    for env_ind, start, end in episodes_start_end
                ]
                num_episode_finished = len(reward_trajs_split)
                episode_reward = np.array(
                    [np.sum(reward_traj) for reward_traj in reward_trajs_split]
                )
                episode_best_reward = np.array(
                    [
                        np.max(reward_traj) / self.act_steps
                        for reward_traj in reward_trajs_split
                    ]
                )
                avg_episode_reward = np.mean(episode_reward)
                avg_best_reward = np.mean(episode_best_reward)
                success_rate = np.mean(
                    episode_best_reward >= self.best_reward_threshold_for_success
                )
            else:
                episode_reward = np.array([])
                num_episode_finished = 0
                avg_episode_reward = 0
                avg_best_reward = 0
                success_rate = 0
                log.info("[WARNING] No episode completed within the iteration!")

            # Update models
            if not eval_mode:
                num_batch = self.replay_ratio

                # Critic learning
                for _ in range(num_batch):
                    # Sample batch
                    inds = np.random.choice(len(obs_buffer), self.batch_size)
                    obs_b = (
                        torch.from_numpy(np.vstack([obs_buffer[i][None] for i in inds]))
                        .float()
                        .to(self.device)
                    )
                    next_obs_b = (
                        torch.from_numpy(
                            np.vstack([next_obs_buffer[i][None] for i in inds])
                        )
                        .float()
                        .to(self.device)
                    )
                    actions_b = (
                        torch.from_numpy(
                            np.vstack([action_buffer[i][None] for i in inds])
                        )
                        .float()
                        .to(self.device)
                    )
                    rewards_b = (
                        torch.from_numpy(np.vstack([reward_buffer[i] for i in inds]))
                        .float()
                        .to(self.device)
                    )
                    dones_b = (
                        torch.from_numpy(np.vstack([done_buffer[i] for i in inds]))
                        .float()
                        .to(self.device)
                    )

                    # Update critic
                    loss_critic = self.model.loss_critic(
                        {"state": obs_b},
                        {"state": next_obs_b},
                        actions_b,
                        rewards_b,
                        dones_b,
                        self.gamma,
                    )
                    self.critic_optimizer.zero_grad()
                    loss_critic.backward()
                    self.critic_optimizer.step()

                # Actor learning
                for _ in range(num_batch):
                    # Sample batch
                    inds = np.random.choice(len(obs_buffer), self.batch_size)
                    obs_b = (
                        torch.from_numpy(np.vstack([obs_buffer[i][None] for i in inds]))
                        .float()
                        .to(self.device)
                    )
                    actions_b = (
                        torch.from_numpy(
                            np.vstack([action_buffer[i][None] for i in inds])
                        )
                        .float()
                        .to(self.device)
                    )

                    # Replace actions in buffer with guided actions
                    guided_action_list = []

                    # get Q-perturbed actions by optimizing
                    actions_flat = actions_b.reshape(actions_b.shape[0], -1)
                    actions_optim = torch.optim.Adam(
                        [actions_flat], lr=self.eta, eps=1e-5
                    )
                    for _ in range(self.action_gradient_steps):
                        actions_flat.requires_grad_(True)
                        q_values_1, q_values_2 = self.model.critic(
                            {"state": obs_b}, actions_flat
                        )
                        q_values = torch.min(q_values_1, q_values_2)
                        action_opt_loss = -q_values.sum()

                        actions_optim.zero_grad()
                        action_opt_loss.backward(torch.ones_like(action_opt_loss))

                        # get the perturbed action
                        actions_optim.step()

                        actions_flat.requires_grad_(False)
                        actions_flat.clamp_(-1.0, 1.0)
                    guided_action = actions_flat.detach()
                    guided_action = guided_action.reshape(
                        guided_action.shape[0], -1, self.action_dim
                    )
                    guided_action_list.append(guided_action)
                    guided_action_stacked = torch.cat(guided_action_list, 0)

                    # Add to buffer (need separate indices since we're working with a limited subset)
                    for i, i_buf in enumerate(inds):
                        action_buffer[i_buf] = (
                            guided_action_stacked[i].detach().cpu().numpy()
                        )

                    # Update policy with collected trajectories
                    loss = self.model.loss(guided_action.detach(), {"state": obs_b})
                    self.actor_optimizer.zero_grad()
                    loss.backward()
                    if self.itr >= self.n_critic_warmup_itr:
                        if self.max_grad_norm is not None:
                            torch.nn.utils.clip_grad_norm_(
                                self.model.actor.parameters(), self.max_grad_norm
                            )
                        self.actor_optimizer.step()

            # Update lr
            self.actor_lr_scheduler.step()
            self.critic_lr_scheduler.step()

            # Save model
            if self.itr % self.save_model_freq == 0 or self.itr == self.n_train_itr - 1:
                self.save_model()

            # Log loss and save metrics
            run_results.append(
                {
                    "itr": self.itr,
                }
            )
            if self.itr % self.log_freq == 0:
                time = timer()
                if eval_mode:
                    log.info(
                        f"eval: success rate {success_rate:8.4f} | avg episode reward {avg_episode_reward:8.4f} | avg best reward {avg_best_reward:8.4f}"
                    )
                    if self.use_wandb:
                        wandb.log(
                            {
                                "success rate - eval": success_rate,
                                "avg episode reward - eval": avg_episode_reward,
                                "avg best reward - eval": avg_best_reward,
                                "num episode - eval": num_episode_finished,
                            },
                            step=self.itr,
                            commit=False,
                        )
                    run_results[-1]["eval_success_rate"] = success_rate
                    run_results[-1]["eval_episode_reward"] = avg_episode_reward
                    run_results[-1]["eval_best_reward"] = avg_best_reward
                else:
                    log.info(
                        f"{self.itr}: loss {loss:8.4f} | reward {avg_episode_reward:8.4f} |t:{time:8.4f}"
                    )
                    if self.use_wandb:
                        wandb.log(
                            {
                                "loss": loss,
                                "loss - critic": loss_critic,
                                "avg episode reward - train": avg_episode_reward,
                                "num episode - train": num_episode_finished,
                            },
                            step=self.itr,
                            commit=True,
                        )
                    run_results[-1]["loss"] = loss
                    run_results[-1]["loss_critic"] = loss_critic
                    run_results[-1]["train_episode_reward"] = avg_episode_reward
                run_results[-1]["time"] = time
                with open(self.result_path, "wb") as f:
                    pickle.dump(run_results, f)
            self.itr += 1