public class SwapSlides {
  private Robot robot;
  private static final int DELAY = 150;

  public static void main(String[] args) {
    SwapSlides swap = new SwapSlides();
    swap.createEnviroment();
    swap.swapAll();
  }

  private void createEnviroment() {
    RobotWorld world = RobotWorld.load("src/swap.txt");
    robot = new Robot(1, world.getNumCols() / 2 , Robot.SOUTH, world);
    robot.setDelay(DELAY);
  }

  //swapping colors on all across cells in the corridor
  //before: the robot is located at the beginning of the corridor, facing the corridor
  //after: the robot has the same location and facing the same direction
  public void swapAll() {
    boolean finished = false;

    while (!finished) {
      swapTwoCells(1);
      if (!atEndOfCorridor())
        robot.move();
      else
        finished = true;
    }
    returnToStartPosition();
  }

  //returns true if the robot is at the end of the corridor, otherwise false
  private boolean atEndOfCorridor() {
    return !robot.frontIsClear();
  }

  // swapping colors of two across cell at position n
  //before: robot is in the corridor facing the corridor
  //after: robot is in the corridor facing the corridor
  private void swapTwoCells(int n) {
    if (leftCellIsDark(n) != rightCellIsDark(n))
      changeColors(n);
  }

  //returns true if the cell on left side of the robot is dark, otherwise false
  //before: robot is in the corridor facing the corridor
  //after: robot is in the corridor facing the corridor
  private boolean leftCellIsDark(int n) {
    robot.turnLeft();
    steps(n);
    boolean isDark = robot.onDark();
    turnAround();
    steps(n);
    robot.turnLeft();
    return isDark;
  }

  //
  private void steps(int n) {
    for (int i = 0; i < n; i = i + 1)
      robot.move();
  }

  //before: none
  //after: robot is facing the opposite direction
  private void turnAround() {
    robot.turnLeft();
    robot.turnLeft();
  }

  //returns true if the cell on right side of the robot is dark, otherwise false
  //before: robot is in the corridor facing the corridor
  //after: robot is in the corridor facing the corridor
  private boolean rightCellIsDark(int n) {
    turnRight();
    steps(n);
    boolean isDark = robot.onDark();
    turnAround();
    steps(n);
    turnRight();
    return isDark;
  }

  //before: none
  //after: robot has turned 90 degree to right
  private void turnRight() {
    turnAround();
    robot.turnLeft();
  }

  //change colors of the cells on left side and on right side of the robot
  //before: robot is in the corridor facing the corridor
  //after: robot is in the corridor facing the corridor
  private void changeColors(int n) {
    changeColorOfLeftCell(n);
    changeColorOfRightCell(n);
  }

  //change color of the cell on left side of the robot
  //before: robot is in the corridor facing the corridor
  //after: robot is in the corridor facing the corridor
  private void changeColorOfLeftCell(int n) {
    robot.turnLeft();
    steps(n);
    switchColor();
    turnAround();
    steps(n);
    robot.turnLeft();
  }

  //change color of the cell on right side of the robot
  //before: robot is in the corridor facing the corridor
  //after: robot is in the corridor facing the corridor
  private void changeColorOfRightCell(int n) {
    turnRight();
    steps(n);
    switchColor();
    turnAround();
    steps(n);
    turnRight();
  }

  //switch color of the cell
  //before: none
  //after: if the cell the robot is at was dark it has become light,
  //          and if the cell was light it has become dark
  private void switchColor() {
    if (robot.onDark())
      robot.makeLight();
    else
      robot.makeDark();
  }

  //before: robot is at end of the corridor, facing the wall
  //after: robot is at beginning of the corridor, facing the corridor
  private void returnToStartPosition() {
    turnAround();
    goToEndOfCorridor();
    turnAround();
  }

  //before: robot is in the corridor, facing the cooridor
  //after: robot is at the end of the corridor, facing the wall
  private void goToEndOfCorridor() {
    while (!atEndOfCorridor()) {
      robot.move();
    }
  }
}