import numpy as np
from gym.envs.mujoco import mujoco_env
from gym import utils


DEFAULT_CAMERA_CONFIG = {}


class SwimmerEnv(mujoco_env.MujocoEnv, utils.EzPickle):
    def __init__(self,
                 xml_file='swimmer.xml',
                 forward_reward_weight=1.0,
                 ctrl_cost_weight=1e-4,
                 reset_noise_scale=0.1,
                 exclude_current_positions_from_observation=True):
        utils.EzPickle.__init__(**locals())

        self._forward_reward_weight = forward_reward_weight
        self._ctrl_cost_weight = ctrl_cost_weight

        self._reset_noise_scale = reset_noise_scale

        self._exclude_current_positions_from_observation = (
            exclude_current_positions_from_observation)

        mujoco_env.MujocoEnv.__init__(self, xml_file, 4)

    def control_cost(self, action):
        control_cost = self._ctrl_cost_weight * np.sum(np.square(action))
        return control_cost

    def step(self, action):
        xy_position_before = self.sim.data.qpos[0:2].copy()
        self.do_simulation(action, self.frame_skip)
        xy_position_after = self.sim.data.qpos[0:2].copy()

        xy_velocity = (xy_position_after - xy_position_before) / self.dt
        x_velocity, y_velocity = xy_velocity

        forward_reward = self._forward_reward_weight * x_velocity

        ctrl_cost = self.control_cost(action)

        observation = self._get_obs()
        reward = forward_reward - ctrl_cost
        done = False
        info = {
            'reward_fwd': forward_reward,
            'reward_ctrl': -ctrl_cost,

            'x_position': xy_position_after[0],
            'y_position': xy_position_after[1],
            'distance_from_origin': np.linalg.norm(xy_position_after, ord=2),

            'x_velocity': x_velocity,
            'y_velocity': y_velocity,
            'forward_reward': forward_reward,
        }

        return observation, reward, done, info

    def _get_obs(self):
        position = self.sim.data.qpos.flat.copy()
        velocity = self.sim.data.qvel.flat.copy()

        if self._exclude_current_positions_from_observation:
            position = position[2:]

        observation = np.concatenate([position, velocity]).ravel()
        return observation

    def reset_model(self):
        noise_low = -self._reset_noise_scale
        noise_high = self._reset_noise_scale

        qpos = self.init_qpos + self.np_random.uniform(
            low=noise_low, high=noise_high, size=self.model.nq)
        qvel = self.init_qvel + self.np_random.uniform(
            low=noise_low, high=noise_high, size=self.model.nv)

        self.set_state(qpos, qvel)

        observation = self._get_obs()
        return observation

    def viewer_setup(self):
        for key, value in DEFAULT_CAMERA_CONFIG.items():
            if isinstance(value, np.ndarray):
                getattr(self.viewer.cam, key)[:] = value
            else:
                setattr(self.viewer.cam, key, value)
