import argparse
import os
import pprint

import gym
import numpy as np
import torch
from torch.utils.tensorboard import SummaryWriter

from tianshou.data import Collector, VectorReplayBuffer
from tianshou.env import SubprocVectorEnv
from tianshou.policy import PPOPolicy
from tianshou.trainer import onpolicy_trainer
from tianshou.utils import TensorboardLogger
from tianshou.utils.net.common import ActorCritic, DataParallelNet, Net
from tianshou.utils.net.discrete import Actor, Critic


def get_args():
    parser = argparse.ArgumentParser()
    parser.add_argument('--task', type=str, default='CartPole-v0')
    parser.add_argument('--seed', type=int, default=0)
    parser.add_argument('--buffer-size', type=int, default=20000)
    parser.add_argument('--lr', type=float, default=3e-4)
    parser.add_argument('--gamma', type=float, default=0.99)
    parser.add_argument('--epoch', type=int, default=10)
    parser.add_argument('--step-per-epoch', type=int, default=50000)
    parser.add_argument('--step-per-collect', type=int, default=2000)
    parser.add_argument('--repeat-per-collect', type=int, default=10)
    parser.add_argument('--batch-size', type=int, default=64)
    parser.add_argument('--hidden-sizes', type=int, nargs='*', default=[64, 64])
    parser.add_argument('--training-num', type=int, default=20)
    parser.add_argument('--test-num', type=int, default=100)
    parser.add_argument('--logdir', type=str, default='log')
    parser.add_argument('--render', type=float, default=0.)
    parser.add_argument(
        '--device', type=str, default='cuda' if torch.cuda.is_available() else 'cpu'
    )
    # ppo special
    parser.add_argument('--vf-coef', type=float, default=0.5)
    parser.add_argument('--ent-coef', type=float, default=0.0)
    parser.add_argument('--eps-clip', type=float, default=0.2)
    parser.add_argument('--max-grad-norm', type=float, default=0.5)
    parser.add_argument('--gae-lambda', type=float, default=0.95)
    parser.add_argument('--rew-norm', type=int, default=0)
    parser.add_argument('--norm-adv', type=int, default=0)
    parser.add_argument('--recompute-adv', type=int, default=0)
    parser.add_argument('--dual-clip', type=float, default=None)
    parser.add_argument('--value-clip', type=int, default=0)
    args = parser.parse_known_args()[0]
    return args


def test_ppo(args=get_args()):
    env = gym.make(args.task)
    args.state_shape = env.observation_space.shape or env.observation_space.n
    args.action_shape = env.action_space.shape or env.action_space.n
    # train_envs = gym.make(args.task)
    # you can also use tianshou.env.SubprocVectorEnv
    train_envs = SubprocVectorEnv(
        [lambda: gym.make(args.task) for _ in range(args.training_num)]
    )
    # test_envs = gym.make(args.task)
    test_envs = SubprocVectorEnv(
        [lambda: gym.make(args.task) for _ in range(args.test_num)]
    )
    # seed
    np.random.seed(args.seed)
    torch.manual_seed(args.seed)
    train_envs.seed(args.seed)
    test_envs.seed(args.seed)
    # model
    net = Net(args.state_shape, hidden_sizes=args.hidden_sizes, device=args.device)
    if torch.cuda.is_available():
        actor = DataParallelNet(
            Actor(net, args.action_shape, device=None).to(args.device)
        )
        critic = DataParallelNet(Critic(net, device=None).to(args.device))
    else:
        actor = Actor(net, args.action_shape, device=args.device).to(args.device)
        critic = Critic(net, device=args.device).to(args.device)
    actor_critic = ActorCritic(actor, critic)
    # orthogonal initialization
    for m in actor_critic.modules():
        if isinstance(m, torch.nn.Linear):
            torch.nn.init.orthogonal_(m.weight)
            torch.nn.init.zeros_(m.bias)
    optim = torch.optim.Adam(actor_critic.parameters(), lr=args.lr)
    dist = torch.distributions.Categorical
    policy = PPOPolicy(
        actor,
        critic,
        optim,
        dist,
        discount_factor=args.gamma,
        max_grad_norm=args.max_grad_norm,
        eps_clip=args.eps_clip,
        vf_coef=args.vf_coef,
        ent_coef=args.ent_coef,
        gae_lambda=args.gae_lambda,
        reward_normalization=args.rew_norm,
        dual_clip=args.dual_clip,
        value_clip=args.value_clip,
        action_space=env.action_space,
        deterministic_eval=True,
        advantage_normalization=args.norm_adv,
        recompute_advantage=args.recompute_adv
    )
    # collector
    train_collector = Collector(
        policy, train_envs, VectorReplayBuffer(args.buffer_size, len(train_envs))
    )
    test_collector = Collector(policy, test_envs)
    # log
    log_path = os.path.join(args.logdir, args.task, 'ppo')
    writer = SummaryWriter(log_path)
    logger = TensorboardLogger(writer)

    def save_fn(policy):
        torch.save(policy.state_dict(), os.path.join(log_path, 'policy.pth'))

    def stop_fn(mean_rewards):
        return mean_rewards >= env.spec.reward_threshold

    # trainer
    result = onpolicy_trainer(
        policy,
        train_collector,
        test_collector,
        args.epoch,
        args.step_per_epoch,
        args.repeat_per_collect,
        args.test_num,
        args.batch_size,
        step_per_collect=args.step_per_collect,
        stop_fn=stop_fn,
        save_fn=save_fn,
        logger=logger
    )
    assert stop_fn(result['best_reward'])

    if __name__ == '__main__':
        pprint.pprint(result)
        # Let's watch its performance!
        env = gym.make(args.task)
        policy.eval()
        collector = Collector(policy, env)
        result = collector.collect(n_episode=1, render=args.render)
        rews, lens = result["rews"], result["lens"]
        print(f"Final reward: {rews.mean()}, length: {lens.mean()}")


if __name__ == '__main__':
    test_ppo()