"""

Path tracking simulation with Stanley steering control and PID speed control.

author: Atsushi Sakai (@Atsushi_twi)

Ref:
 - [Stanley: The robot that won the DARPA grand challenge](http://isl.ecst.csuchico.edu/DOCS/darpa2005/DARPA%202005%20Stanley.pdf)
 - [Autonomous Automobile Path Tracking](https://www.ri.cmu.edu/pub_files/2009/2/Automatic_Steering_Methods_for_Autonomous_Automobile_Path_Tracking.pdf)

"""
import numpy as np
import matplotlib.pyplot as plt
import sys
import os

sys.path.append(os.path.dirname(os.path.abspath(__file__)) +
 "/../../PathPlanning/CubicSpline/")

try:
 import cubic_spline_planner
except:
 raise


k = 0.5 # control gain
Kp = 1.0 # speed proportional gain
dt = 0.1 # [s] time difference
L = 2.9 # [m] Wheel base of vehicle
max_steer = np.radians(30.0) # [rad] max steering angle

show_animation = True


class State(object):
 """
 Class representing the state of a vehicle.

 :param x: (float) x-coordinate
 :param y: (float) y-coordinate
 :param yaw: (float) yaw angle
 :param v: (float) speed
 """

 def __init__(self, x=0.0, y=0.0, yaw=0.0, v=0.0):
 """Instantiate the object."""
 super(State, self).__init__()
 self.x = x
 self.y = y
 self.yaw = yaw
 self.v = v

 def update(self, acceleration, delta):
 """
 Update the state of the vehicle.

 Stanley Control uses bicycle model.

 :param acceleration: (float) Acceleration
 :param delta: (float) Steering
 """
 delta = np.clip(delta, -max_steer, max_steer)

 self.x += self.v * np.cos(self.yaw) * dt
 self.y += self.v * np.sin(self.yaw) * dt
 self.yaw += self.v / L * np.tan(delta) * dt
 self.yaw = normalize_angle(self.yaw)
 self.v += acceleration * dt


def pid_control(target, current):
 """
 Proportional control for the speed.

 :param target: (float)
 :param current: (float)
 :return: (float)
 """
 return Kp * (target - current)


def stanley_control(state, cx, cy, cyaw, last_target_idx):
 """
 Stanley steering control.

 :param state: (State object)
 :param cx: ([float])
 :param cy: ([float])
 :param cyaw: ([float])
 :param last_target_idx: (int)
 :return: (float, int)
 """
 current_target_idx, error_front_axle = calc_target_index(state, cx, cy)

 if last_target_idx >= current_target_idx:
 current_target_idx = last_target_idx

 # theta_e corrects the heading error
 theta_e = normalize_angle(cyaw[current_target_idx] - state.yaw)
 # theta_d corrects the cross track error
 theta_d = np.arctan2(k * error_front_axle, state.v)
 # Steering control
 delta = theta_e + theta_d

 return delta, current_target_idx


def normalize_angle(angle):
 """
 Normalize an angle to [-pi, pi].

 :param angle: (float)
 :return: (float) Angle in radian in [-pi, pi]
 """
 while angle > np.pi:
 angle -= 2.0 * np.pi

 while angle < -np.pi:
 angle += 2.0 * np.pi

 return angle


def calc_target_index(state, cx, cy):
 """
 Compute index in the trajectory list of the target.

 :param state: (State object)
 :param cx: [float]
 :param cy: [float]
 :return: (int, float)
 """
 # Calc front axle position
 fx = state.x + L * np.cos(state.yaw)
 fy = state.y + L * np.sin(state.yaw)

 # Search nearest point index
 dx = [fx - icx for icx in cx]
 dy = [fy - icy for icy in cy]
 d = np.hypot(dx, dy)
 target_idx = np.argmin(d)

 # Project RMS error onto front axle vector
 front_axle_vec = [-np.cos(state.yaw + np.pi / 2),
 -np.sin(state.yaw + np.pi / 2)]
 error_front_axle = np.dot([dx[target_idx], dy[target_idx]], front_axle_vec)

 return target_idx, error_front_axle


def main():
 """Plot an example of Stanley steering control on a cubic spline."""
 # target course
 ax = [0.0, 100.0, 100.0, 50.0, 60.0]
 ay = [0.0, 0.0, -30.0, -20.0, 0.0]

 cx, cy, cyaw, ck, s = cubic_spline_planner.calc_spline_course(
 ax, ay, ds=0.1)

 target_speed = 30.0 / 3.6 # [m/s]

 max_simulation_time = 100.0

 # Initial state
 state = State(x=-0.0, y=5.0, yaw=np.radians(20.0), v=0.0)

 last_idx = len(cx) - 1
 time = 0.0
 x = [state.x]
 y = [state.y]
 yaw = [state.yaw]
 v = [state.v]
 t = [0.0]
 target_idx, _ = calc_target_index(state, cx, cy)

 while max_simulation_time >= time and last_idx > target_idx:
 ai = pid_control(target_speed, state.v)
 di, target_idx = stanley_control(state, cx, cy, cyaw, target_idx)
 state.update(ai, di)

 time += dt

 x.append(state.x)
 y.append(state.y)
 yaw.append(state.yaw)
 v.append(state.v)
 t.append(time)

 if show_animation: # pragma: no cover
 plt.cla()
 # for stopping simulation with the esc key.
 plt.gcf().canvas.mpl_connect('key_release_event',
 lambda event: [exit(0) if event.key == 'escape' else None])
 plt.plot(cx, cy, ".r", label="course")
 plt.plot(x, y, "-b", label="trajectory")
 plt.plot(cx[target_idx], cy[target_idx], "xg", label="target")
 plt.axis("equal")
 plt.grid(True)
 plt.title("Speed[km/h]:" + str(state.v * 3.6)[:4])
 plt.pause(0.001)

 # Test
 assert last_idx >= target_idx, "Cannot reach goal"

 if show_animation: # pragma: no cover
 plt.plot(cx, cy, ".r", label="course")
 plt.plot(x, y, "-b", label="trajectory")
 plt.legend()
 plt.xlabel("x[m]")
 plt.ylabel("y[m]")
 plt.axis("equal")
 plt.grid(True)

 plt.subplots(1)
 plt.plot(t, [iv * 3.6 for iv in v], "-r")
 plt.xlabel("Time[s]")
 plt.ylabel("Speed[km/h]")
 plt.grid(True)
 plt.show()


if __name__ == '__main__':
 main()