import threading
import time

class ControllerBase:
    def __init__(self, control_rate=0.1):
        self.robot = None
        self.controlling = False
        self.target_pos = None

        self.control_thread = None
        self.control_rate = control_rate

    def control_loop(self):
        while self.controlling:
            if self.target_pos is not None:
                state = self.get_measured_position()

                control = self.compute_control(state)

                self.apply_control(control)

                time.sleep(self.control_rate)
        self.apply_control((0.0,0.0))   # stop robot

    def set_target_position(self, target_pos):
        self.target_pos = target_pos

    def get_measured_position(self):
        if self.robot is not None:
            return self.robot.get_measurement()
        else:
            raise Exception("error: controller cannot get measurement!\n       there is no robot attached to the controller!")

    def compute_control(self, state):
        return (0.0, 0.0)

    def apply_control(self, control):
        if self.robot is not None:
            self.robot.send_cmd(u1=control[0], u2=control[1])
        else:
            raise Exception("error: controller cannot apply control!\n       there is no robot attached to the controller!")

    def attach_robot(self, robot):
        self.robot = robot

    def start(self):
        self.controlling = True
        # start control thread
        self.control_thread = threading.Thread(target=self.control_loop)
        self.control_thread.start()

    def stop(self):
        # pause controller
        self.controlling = False
        if self.control_thread is not None:
            self.control_thread.join()