import numpy as np
import gym
from gym.envs.mujoco.mujoco_env import MujocoEnv
from ray.rllib.env.apis.task_settable_env import TaskSettableEnv


class HalfCheetahRandDirecEnv(MujocoEnv, gym.utils.EzPickle, TaskSettableEnv):
    """HalfCheetah Environment with two diff tasks, moving forwards or backwards

    Direction is defined as a scalar: +1.0 (forwards) or -1.0 (backwards)
    """

    def __init__(self, goal_direction=None):
        self.goal_direction = goal_direction if goal_direction else 1.0
        MujocoEnv.__init__(self, "half_cheetah.xml", 5)
        gym.utils.EzPickle.__init__(self, goal_direction)

    def sample_tasks(self, n_tasks):
        # For fwd/bwd env, goal direc is backwards if - 1.0, forwards if + 1.0
        return np.random.choice((-1.0, 1.0), (n_tasks, ))

    def set_task(self, task):
        """
        Args:
            task: task of the meta-learning environment
        """
        self.goal_direction = task

    def get_task(self):
        """
        Returns:
            task: task of the meta-learning environment
        """
        return self.goal_direction

    def step(self, action):
        xposbefore = self.sim.data.qpos[0]
        self.do_simulation(action, self.frame_skip)
        xposafter = self.sim.data.qpos[0]
        ob = self._get_obs()
        reward_ctrl = -0.5 * 0.1 * np.square(action).sum()
        reward_run = self.goal_direction * (xposafter - xposbefore) / self.dt
        reward = reward_ctrl + reward_run
        done = False
        return ob, reward, done, dict(
            reward_run=reward_run, reward_ctrl=reward_ctrl)

    def _get_obs(self):
        return np.concatenate([
            self.sim.data.qpos.flat[1:],
            self.sim.data.qvel.flat,
        ])

    def reset_model(self):
        qpos = self.init_qpos + self.np_random.uniform(
            low=-.1, high=.1, size=self.model.nq)
        qvel = self.init_qvel + self.np_random.randn(self.model.nv) * .1
        self.set_state(qpos, qvel)
        obs = self._get_obs()
        return obs

    def viewer_setup(self):
        self.viewer.cam.distance = self.model.stat.extent * 0.5