// traffic simulation
// this time, just the cars, but they move at high speed for the first 200 pixels, and a lower speed for the rest.
// they are supposed to not get within 20 pixels of each other, but this seems not to be working.

import colors.*;
import geometry.*;
import idraw.*;

// interface for objects in the simulation world.
// all objects in the world must be able to respond to onTick and draw.
interface IObj {
  void onTick();
  void draw(Canvas c);
}

class NullObj implements IObj {
  
  void onTick() {
    return;
  }
  
  void draw(Canvas c) {
    return;
  } 
}


// composite object. draw(), onTick() are sent to first, then second.
class ConsObj implements IObj {
  IObj first;
  IObj second;
  
  ConsObj (IObj first, IObj second) {
    this.first = first;
    this.second = second;
  }  
  
  void onTick() {
    this.first.onTick();
    this.second.onTick();
    return;
  }
  
  void draw(Canvas c) {
    this.first.draw(c);
    this.second.draw(c);
    return;
  } 
}


// interface to avoid introducing null
interface ICar extends IObj {
  int getRearLoc();
}

// class for the non-existent car in front of the first real car
// it is always moving and sits at x=999999; otherwise it doesn't do anything.

// I'd like this to say "implements ICar extends NullObj", but this doesn't seem to work.
class NullCar implements ICar {
  
  NullCar(){  }
  
  void onTick() {
    return;
  }
  
  void draw(Canvas c) {
    return;
  } 

  int getRearLoc(){
    return 999999;
  }
  
}

// A real car.  Enters at x=0, records the time since its creation.
class Car implements ICar {
  Posn p;    // position of left (rear) bumper
  int time;  // time since its creation
  
  ICar carAhead;
  TWorld w;

  int speed1 = 20;
  int speed2 = 4;
  int gap = 20;
  int WIDTH = 20;
  int HEIGHT = 10;
  IColor color = new Blue();
  
  // create a car at Posn p, following carAhead.
  Car(int x, ICar carAhead, TWorld w) {
    this.p = new Posn(x, w.HEIGHT-this.HEIGHT);
    this.carAhead = carAhead;
    this.w = w;
    this.time = 0;
    w.addCar(this);    // register the car
  }

  void onTick(){
    this.time = this.time+1;
    int nextx = 0;
    int carAheadRearLoc = this.carAhead.getRearLoc();
    if (this.p.x < 200) {
      // we are to the left of the halfway mark
      nextx = this.p.x+this.speed1;
    } else {
      // we are to the right of the 500 px mark
      nextx = this.p.x+this.speed2;
      // this.color = new Green();
    }   

    if (carAheadRearLoc - nextx < this.gap + this.WIDTH) {
      // this.color = new Yellow();
      nextx = carAheadRearLoc - this.gap - this.WIDTH;
    } else {}    
    this.p = new Posn (nextx, this.p.y);
    return;
 }
  
  void draw(Canvas c){
    c.drawRect(this.p, this.WIDTH, this.HEIGHT, this.color);
    return;
  }
  
  int getRearLoc(){
    return this.p.x;
  }
    
}

// create a new car into world w every period ticks
class CarMaker extends NullObj {
  TWorld w;
  int period;
  int counter;
  ICar previousCar;
  
  CarMaker (int period, TWorld w) {
    this.w = w;
    this.period = period;
    this.counter = 0;
    this.previousCar = new NullCar();
    w.addObj(this);    // register to receive ticks only
  }
  
  void onTick () {
    if (this.counter >= this.period) {
      // time to create a new car.  Also reset the counter.
      Car newCar = new Car(0, this.previousCar, w);
      this.previousCar = newCar;
      this.counter = 0;
      return;
    } else {
      this.counter = this.counter + 1;
      return;
    }
  }
}

class TWorld extends World {
  
  int WIDTH = 1000;
  int HEIGHT = 100;
  double rate = 0.25;
  
  IObj cars = new NullObj();
  IObj lights = new NullObj();
  IObj otherObjs = new NullObj(); 
  
  TWorld (){
    
  }
  
  void addCar(Car c){
    this.cars = new ConsObj(this.cars, c);
  }
/*  
  void addLight(TrafficLight t) {
    this.lights = new ConsObj(this.lights, t);
  }
*/  
  void addObj(IObj o) {
    this.otherObjs = new ConsObj(this.otherObjs, o);
  }
  
  void start(){
    this.bigBang(this.WIDTH, this.HEIGHT, this.rate);
  }

  void onTick(){
    this.cars.onTick();
    // this.lights.onTick();
    this.otherObjs.onTick();
    return;
  }
  
  void draw(){
    this.cars.draw(this.theCanvas);
    // this.lights.draw(this.theCanvas);
    return;
  }
  
  void onKeyEvent(String s){
    return;
  }
  
}

class Examples {
  TWorld w = new TWorld();
  Examples () {
    // ICar car1 = new Car(100, new NullCar(), w);
    // ICar car2 = new Car(0, car1, w);
    CarMaker carMaker1 = new CarMaker(2,w);
    w.start();
  }
}