import os
os.sys.path.append(os.path.join(os.path.dirname(os.path.realpath(__file__)), '..'))
import numpy as np
import torch
from torch.optim import Adam
import gym
import time
import copy
import trpo_core as core
from utils.logx import EpochLogger, setup_logger_kwargs, colorize
from utils.mpi_pytorch import setup_pytorch_for_mpi, sync_params, mpi_avg_grads
from utils.mpi_tools import mpi_fork, mpi_avg, proc_id, mpi_statistics_scalar, num_procs, mpi_sum
 
from safety_gym_arm.envs.engine import Engine as safety_gym_arm_Engine
from utils.safetygym_config import configuration
import os.path as osp

device = torch.device("cuda:6" if torch.cuda.is_available() else "cpu")
EPS = 1e-8

class TRPOBuffer:

    def __init__(self, obs_dim, act_dim, size, gamma=0.99, lam=0.95):
        self.obs_buf = np.zeros(core.combined_shape(size, obs_dim), dtype=np.float32)
        self.act_buf = np.zeros(core.combined_shape(size, act_dim), dtype=np.float32)
        self.adv_buf = np.zeros(size, dtype=np.float32)
        self.rew_buf = np.zeros(size, dtype=np.float32)
        self.ret_buf = np.zeros(size, dtype=np.float32)
        self.val_buf = np.zeros(size, dtype=np.float32)
        self.logp_buf = np.zeros(size, dtype=np.float32)
        self.mu_buf = np.zeros(core.combined_shape(size, act_dim), dtype=np.float32)
        self.logstd_buf = np.zeros(core.combined_shape(size, act_dim), dtype=np.float32)
        self.gamma, self.lam = gamma, lam
        self.ptr, self.path_start_idx, self.max_size = 0, 0, size

    def store(self, obs, act, rew, val, logp, mu, logstd):
        """
        Append one timestep of agent-environment interaction to the buffer.
        """
        assert self.ptr < self.max_size     # buffer has to have room so you can store
        self.obs_buf[self.ptr] = obs
        self.act_buf[self.ptr] = act
        self.rew_buf[self.ptr] = rew
        self.val_buf[self.ptr] = val
        self.logp_buf[self.ptr] = logp
        self.mu_buf[self.ptr] = mu
        self.logstd_buf[self.ptr] = logstd
        self.ptr += 1

    def finish_path(self, last_val=0):
        """
        Call this at the end of a trajectory, or when one gets cut off
        by an epoch ending. This looks back in the buffer to where the
        trajectory started, and uses rewards and value estimates from
        the whole trajectory to compute advantage estimates with GAE-Lambda,
        as well as compute the rewards-to-go for each state, to use as
        the targets for the value function.

        The "last_val" argument should be 0 if the trajectory ended
        because the agent reached a terminal state (died), and otherwise
        should be V(s_T), the value function estimated for the last state.
        This allows us to bootstrap the reward-to-go calculation to account
        for timesteps beyond the arbitrary episode horizon (or epoch cutoff).
        """

        path_slice = slice(self.path_start_idx, self.ptr)
        rews = np.append(self.rew_buf[path_slice], last_val)
        vals = np.append(self.val_buf[path_slice], last_val)
        
        # the next two lines implement GAE-Lambda advantage calculation
        deltas = rews[:-1] + self.gamma * vals[1:] - vals[:-1]
        self.adv_buf[path_slice] = core.discount_cumsum(deltas, self.gamma * self.lam)
        
        # the next line computes rewards-to-go, to be targets for the value function
        self.ret_buf[path_slice] = core.discount_cumsum(rews, self.gamma)[:-1]
        
        self.path_start_idx = self.ptr

    def get(self):
        """
        Call this at the end of an epoch to get all of the data from
        the buffer, with advantages appropriately normalized (shifted to have
        mean zero and std one). Also, resets some pointers in the buffer.
        """
        assert self.ptr == self.max_size    # buffer has to be full before you can get
        self.ptr, self.path_start_idx = 0, 0
        # the next two lines implement the advantage normalization trick
        adv_mean, adv_std = mpi_statistics_scalar(self.adv_buf)
        self.adv_buf = (self.adv_buf - adv_mean) / adv_std
        data = dict(obs=torch.FloatTensor(self.obs_buf).to(device), 
                    act=torch.FloatTensor(self.act_buf).to(device), 
                    ret=torch.FloatTensor(self.ret_buf).to(device),
                    adv=torch.FloatTensor(self.adv_buf).to(device), 
                    logp=torch.FloatTensor(self.logp_buf).to(device),
                    mu=torch.FloatTensor(self.mu_buf).to(device),
                    logstd=torch.FloatTensor(self.logstd_buf).to(device),
        )
        return {k: torch.as_tensor(v, dtype=torch.float32) for k,v in data.items()}


def get_net_param_np_vec(net):
    """
        Get the parameters of the network as numpy vector
    """
    return torch.cat([val.flatten() for val in net.parameters()], axis=0).detach().cpu().numpy()

def assign_net_param_from_flat(param_vec, net):
    param_sizes = [np.prod(list(val.shape)) for val in net.parameters()]
    ptr = 0
    for s, param in zip(param_sizes, net.parameters()):
        param.data.copy_(torch.from_numpy(param_vec[ptr:ptr+s]).reshape(param.shape))
        ptr += s

def cg(Ax, b, cg_iters=100):
    x = np.zeros_like(b)
    r = b.copy() # Note: should be 'b - Ax', but for x=0, Ax=0. Change if doing warm start.
    p = r.copy()
    r_dot_old = np.dot(r,r)
    for _ in range(cg_iters):
        z = Ax(p)
        alpha = r_dot_old / (np.dot(p, z) + EPS)
        x += alpha * p
        r -= alpha * z
        r_dot_new = np.dot(r,r)
        p = r + (r_dot_new / r_dot_old) * p
        r_dot_old = r_dot_new
        # early stopping 
        if np.linalg.norm(p) < EPS:
            break
    return x

def auto_grad(objective, net, to_numpy=True):
    """
    Get the gradient of the objective with respect to the parameters of the network
    """
    grad = torch.autograd.grad(objective, net.parameters(), create_graph=True)
    if to_numpy:
        return torch.cat([val.flatten() for val in grad], axis=0).detach().cpu().numpy()
    else:
        return torch.cat([val.flatten() for val in grad], axis=0)

def auto_hession_x(objective, net, x):
    """
    Returns 
    """
    jacob = auto_grad(objective, net, to_numpy=False)
    
    return auto_grad(torch.dot(jacob, x), net, to_numpy=True)

def trpo(env_fn, actor_critic=core.MLPActorCritic, ac_kwargs=dict(), seed=0, 
        steps_per_epoch=4000, epochs=50, gamma=0.99, clip_ratio=0.2, pi_lr=3e-4,
        vf_lr=1e-3, train_pi_iters=80, train_v_iters=80, lam=0.97, max_ep_len=1000,
        target_kl=0.01, logger_kwargs=dict(), save_freq=10, backtrack_coeff=0.8, backtrack_iters=100, model_save=False):

    # Special function to avoid certain slowdowns from PyTorch + MPI combo.
    setup_pytorch_for_mpi()

    # Set up logger and save configuration
    logger = EpochLogger(**logger_kwargs)
    logger.save_config(locals())

    # Random seed
    seed += 10000 * proc_id()
    torch.manual_seed(seed)
    np.random.seed(seed)

    # Instantiate environment
    env = env_fn()
    obs_dim = env.observation_space.shape
    act_dim = env.action_space.shape

    # Create actor-critic module
    ac = actor_critic(env.observation_space, env.action_space, **ac_kwargs).to(device)

    # Sync params across processes
    sync_params(ac)

    # Count variables
    var_counts = tuple(core.count_vars(module) for module in [ac.pi, ac.v])
    logger.log('\nNumber of parameters: \t pi: %d, \t v: %d\n'%var_counts)

    # Set up experience buffer
    local_steps_per_epoch = int(steps_per_epoch / num_procs())
    buf = TRPOBuffer(obs_dim, act_dim, local_steps_per_epoch, gamma, lam)


    def compute_kl_pi(data, cur_pi):
        """
        Return the sample average KL divergence between old and new policies
        """
        obs, act, adv, logp_old, mu_old, logstd_old = data['obs'], data['act'], data['adv'], data['logp'], data['mu'], data['logstd']
        
        # Average KL Divergence  
        pi, logp = cur_pi(obs, act)
        # average_kl = (logp_old - logp).mean()
        average_kl = cur_pi._d_kl(
            torch.as_tensor(obs, dtype=torch.float32),
            torch.as_tensor(mu_old, dtype=torch.float32),
            torch.as_tensor(logstd_old, dtype=torch.float32), device=device)
        
        return average_kl


    def compute_loss_pi(data, cur_pi):
        """
        The reward objective for TRPO (TRPO policy loss)
        """
        obs, act, adv, logp_old = data['obs'], data['act'], data['adv'], data['logp']
        
        # Policy loss 
        pi, logp = cur_pi(obs, act)
        # loss_pi = -(logp * adv).mean()
        ratio = torch.exp(logp - logp_old)
        loss_pi = -(ratio * adv).mean()
        
        # Useful extra info
        approx_kl = (logp_old - logp).mean().item()
        ent = pi.entropy().mean().item()
        pi_info = dict(kl=approx_kl, ent=ent)
        
        return loss_pi, pi_info
        

    # Set up function for computing value loss
    def compute_loss_v(data):
        obs, ret = data['obs'], data['ret']
        return ((ac.v(obs) - ret)**2).mean()

    # Set up optimizers for policy and value function
    vf_optimizer = Adam(ac.v.parameters(), lr=vf_lr)

    # Set up model saving
    if model_save:
        logger.setup_pytorch_saver(ac)

    def update():
        data = buf.get()

        pi_l_old, pi_info_old = compute_loss_pi(data, ac.pi)
        pi_l_old = pi_l_old.item()
        v_l_old = compute_loss_v(data).item()


        # TRPO policy update core impelmentation 
        loss_pi, pi_info = compute_loss_pi(data, ac.pi)
        g = auto_grad(loss_pi, ac.pi) # get the flatten gradient evaluted at pi old 
        kl_div = compute_kl_pi(data, ac.pi)
        Hx = lambda x: auto_hession_x(kl_div, ac.pi, torch.FloatTensor(x).to(device))
        x_hat    = cg(Hx, g)             # Hinv_g = H \ g
        
        s = x_hat.T @ Hx(x_hat)
        s_ep = s if s < 0. else 1 # log s negative appearence 
            
        # x_direction = np.sqrt(2 * target_kl / (np.clip(s,0.,None)+EPS)) * x_hat
        x_direction = np.sqrt(2 * target_kl / (s+EPS)) * x_hat
        
        # copy an actor to conduct line search 
        actor_tmp = copy.deepcopy(ac.pi)
        def set_and_eval(step):
            new_param = get_net_param_np_vec(ac.pi) - step * x_direction
            assign_net_param_from_flat(new_param, actor_tmp)
            kl = compute_kl_pi(data, actor_tmp)
            pi_l, _ = compute_loss_pi(data, actor_tmp)
            
            return kl, pi_l
        
        # update the policy such that the KL diveragence constraints are satisfied and loss is decreasing
        for j in range(backtrack_iters):
            try:
                kl, pi_l_new = set_and_eval(backtrack_coeff**j)
            except:
                import ipdb; ipdb.set_trace()
            
            if (kl.item() <= target_kl and pi_l_new.item() <= pi_l_old):
                print(colorize(f'Accepting new params at step %d of line search.'%j, 'green', bold=False))
                # update the policy parameter 
                new_param = get_net_param_np_vec(ac.pi) - backtrack_coeff**j * x_direction
                assign_net_param_from_flat(new_param, ac.pi)
                loss_pi, pi_info = compute_loss_pi(data, ac.pi) # re-evaluate the pi_info for the new policy
                break
            if j==backtrack_iters-1:
                print(colorize(f'Line search failed! Keeping old params.', 'yellow', bold=False))

        # Value function learning
        for i in range(train_v_iters):
            vf_optimizer.zero_grad()
            loss_v = compute_loss_v(data)
            loss_v.backward()
            mpi_avg_grads(ac.v)    # average grads across MPI processes
            vf_optimizer.step()

        # Log changes from update        
        kl, ent = pi_info['kl'], pi_info_old['ent']
        logger.store(LossPi=pi_l_old, LossV=v_l_old,
                     KL=kl, Entropy=ent,
                     DeltaLossPi=(loss_pi.item() - pi_l_old),
                     DeltaLossV=(loss_v.item() - v_l_old),
                     EpochS = s_ep)

    # Prepare for interaction with environment
    start_time = time.time()
    # o, ep_ret, ep_len = env.reset(), 0, 0
    while True:
        try:
            o, ep_ret, ep_len = env.reset(), 0, 0
            break
        except:
            print('reset environment is wrong, try next reset')
    ep_cost, cum_cost = 0, 0

    # Main loop: collect experience in env and update/log each epoch
    for epoch in range(epochs):
        for t in range(local_steps_per_epoch):
            a, v, logp, mu, logstd = ac.step(torch.as_tensor(o, dtype=torch.float32))
                    
            try: 
                next_o, r, d, info = env.step(a)
                assert 'cost' in info.keys()
            except: 
                # simulation exception discovered, discard this episode 
                next_o, r, d = o, 0, True # observation will not change, no reward when episode done 
                info['cost'] = 0 # no cost when episode done 
            
            # Track cumulative cost over training
            cum_cost += info['cost']
            
            ep_ret += r
            ep_len += 1
            ep_cost += info['cost']

            # save and log
            buf.store(o, a, r, v, logp, mu, logstd)
            logger.store(VVals=v)
            
            # Update obs (critical!)
            o = next_o

            timeout = ep_len == max_ep_len
            terminal = d or timeout
            epoch_ended = t==local_steps_per_epoch-1

            if terminal or epoch_ended:
                if epoch_ended and not(terminal):
                    print('Warning: trajectory cut off by epoch at %d steps.'%ep_len, flush=True)
                # if trajectory didn't reach terminal state, bootstrap value target
                if timeout or epoch_ended:
                    _, v, _, _, _ = ac.step(torch.as_tensor(o, dtype=torch.float32))
                else:
                    v = 0
                buf.finish_path(v)
                if terminal:
                    # only save EpRet / EpLen / EpCost if trajectory finished
                    logger.store(EpRet=ep_ret, EpLen=ep_len, EpCost=ep_cost)
                # o, ep_ret, ep_len = env.reset(), 0, 0
                while True:
                    try:
                        o, ep_ret, ep_len = env.reset(), 0, 0
                        break
                    except:
                        print('reset environment is wrong, try next reset')
                ep_cost = 0 # episode cost is zero 

        # Save model
        if ((epoch % save_freq == 0) or (epoch == epochs-1)) and model_save:
            logger.save_state({'env': env}, None)

        # Perform TRPO update!
        update()
        
        #=====================================================================#
        #  Cumulative cost calculations                                       #
        #=====================================================================#
        cumulative_cost = mpi_sum(cum_cost)
        cost_rate = cumulative_cost / ((epoch+1)*steps_per_epoch)

        # Log info about epoch
        logger.log_tabular('Epoch', epoch)
        logger.log_tabular('EpRet', with_min_and_max=True)
        logger.log_tabular('EpCost', with_min_and_max=True)
        logger.log_tabular('EpLen', average_only=True)
        logger.log_tabular('CumulativeCost', cumulative_cost)
        logger.log_tabular('CostRate', cost_rate)
        logger.log_tabular('VVals', with_min_and_max=True)
        logger.log_tabular('TotalEnvInteracts', (epoch+1)*steps_per_epoch)
        logger.log_tabular('LossPi', average_only=True)
        logger.log_tabular('LossV', average_only=True)
        logger.log_tabular('DeltaLossPi', average_only=True)
        logger.log_tabular('DeltaLossV', average_only=True)
        logger.log_tabular('Entropy', average_only=True)
        logger.log_tabular('KL', average_only=True)
        logger.log_tabular('Time', time.time()-start_time)
        logger.log_tabular('EpochS', average_only=True)
        logger.dump_tabular()
        
        
def create_env(args):
    env = safety_gym_arm_Engine(configuration(args.task))
    return env

if __name__ == '__main__':
    import argparse
    parser = argparse.ArgumentParser()    
    parser.add_argument('--task', type=str, default='Mygoal4')
    parser.add_argument('--hazards_size', type=float, default=0.30)  # the default hazard size of safety gym 
    parser.add_argument('--hid', type=int, default=64)
    parser.add_argument('--l', type=int, default=2)
    parser.add_argument('--gamma', type=float, default=0.99)
    parser.add_argument('--seed', '-s', type=int, default=0)
    parser.add_argument('--cpu', type=int, default=1)
    parser.add_argument('--steps', type=int, default=30000)
    parser.add_argument('--max_ep_len', type=int, default=1000)
    parser.add_argument('--epochs', type=int, default=200)
    parser.add_argument('--exp_name', type=str, default='trpo')
    parser.add_argument('--model_save', action='store_true')
    parser.add_argument('--target_kl', type=float, default=0.02)
    args = parser.parse_args()

    mpi_fork(args.cpu)  # run parallel code with mpi
    
    exp_name = args.task + '_' + args.exp_name + '_' + 'kl' + str(args.target_kl) + '_' + 'epochs' + str(args.epochs)
    logger_kwargs = setup_logger_kwargs(exp_name, args.seed)

    # whether to save model
    # model_save = True if args.model_save else False
    model_save = True

    trpo(lambda : create_env(args), actor_critic=core.MLPActorCritic,
        ac_kwargs=dict(hidden_sizes=[args.hid]*args.l), gamma=args.gamma, 
        seed=args.seed, steps_per_epoch=args.steps, epochs=args.epochs,
        logger_kwargs=logger_kwargs, model_save=model_save, target_kl=args.target_kl, max_ep_len=args.max_ep_len)