int gameScreen = 0;
int ballX, ballY;
int ballSize = 20;
int ballColor = color(0);
float gravity = 1;
float ballSpeedVert = 0;
float airFriction = 0.0001;
float friction = 0.1;
color racketColor = color(0);
float racketWidth = 100;
float racketHeight = 10;
int racketBounceRate = 20;
float ballSpeedHorizon = 10;

int wallSpeed = 5;
int wallInterval = 1000;
float lastAddTime = 0;
int minGapHeight = 200;
int maxGapHeight = 300;
int wallWidth = 80;
color wallColors = color(0);
ArrayList<int[]> walls = new ArrayList<int[]>();
void setup()
{
  size(500,500);
  ballX=width/4;
  ballY=height/5;
}
void draw()
{
  if(gameScreen == 0) initScreen();
  if(gameScreen == 1) gameScreen();
  if(gameScreen == 2) gameOverScreen();
}
void initScreen()
{
  background(0);
  textAlign(CENTER);
  text("Click to start", height/2, width/2);
}
void gameScreen()
{
  background(255);
  drawBall();
  applyGravity();
  watchRacketBounce();
  keepInScreen();
  drawRacket();
  applyHorizontalSpeed();
  wallAdder();
  wallHandler();
}
void gameOverScreen()
{

}
public void mousePressed()
{
  if(gameScreen == 0) startGame();
}
void startGame()
{
  gameScreen=1;
}
void drawBall()
{
  fill(ballColor);
  ellipse(ballX, ballY, ballSize, ballSize);
}
void applyGravity()
{
  ballSpeedVert += gravity;
  ballY += ballSpeedVert;
  ballSpeedVert -= ballSpeedVert * airFriction;
}
void keepInScreen()
{
  if(ballY+(ballSize/2) > height) makeBounceBottom(height);
  if(ballY-(ballSize/2) < 0) makeBounceTop(0);
  if(ballX-(ballSize/2) < 0) makeBounceLeft(0);
  if(ballX+(ballSize/2) > width) makeBounceRight(width);
}
void makeBounceBottom(int surface)
{
  ballY = surface - (ballSize/2);
  ballSpeedVert *= -1;
  ballSpeedVert -= ballSpeedVert * friction;
}
void makeBounceTop(int surface)
{
  ballY = surface + (ballSize/2);
  ballSpeedVert *= -1;
  ballSpeedVert -= ballSpeedVert * friction;
}
void drawRacket()
{
  fill(racketColor);
  rectMode(CENTER);
  rect(mouseX,mouseY,racketWidth,racketHeight);
}
void watchRacketBounce()
{
  float overhead = mouseY - pmouseY;
  if((ballX+(ballSize/2) > mouseX - (racketWidth/2)) &&
    (ballX-(ballSize/2) < mouseX + (racketWidth/2)))
    {
      if(dist(ballX,ballY, ballX, mouseY) <=(ballSize/2)+abs(overhead))
      {
        makeBounceBottom(mouseY);
        ballSpeedHorizon = (ballX-mouseX)/5;
        if(overhead<0)
        {
          ballY+=overhead;
          ballSpeedVert+=overhead;
        }
      }
    }
}
void applyHorizontalSpeed()
{
  ballX += ballSpeedHorizon;
  ballSpeedHorizon -= (ballSpeedHorizon * airFriction);
}
void makeBounceLeft(int surface)
{
  ballX = surface +(ballSize/2);
  ballSpeedHorizon *= -1;
  ballSpeedHorizon -= ballSpeedHorizon * friction;
}
void makeBounceRight(int surface)
{
  ballX = surface -(ballSize/2);
  ballSpeedHorizon *= -1;
  ballSpeedHorizon -= ballSpeedHorizon * friction;
}
void wallAdder()
{
  if(millis()-lastAddTime>wallInterval)
  {
    int randHeight = round(random(minGapHeight, maxGapHeight));
    int randY = round(random(0,height-randHeight));
    int[] randWall = {width, randY, wallWidth, randHeight};
    walls.add(randWall);
    lastAddTime = millis();
  }
}
void wallHandler()
{
  for(int i = 0; i<walls.size(); i++)
  {
    wallRemover(i);
    wallMover(i);
    watchWallCollision(i);
    wallDrawer(i);
  }
}
void wallRemover(int index)
{
  int[] wall = walls.get(index);
  if(wall[0] + wall[2] <=0) walls.remove(index);
}
void wallMover(int index)
{
  int[] wall = walls.get(index);
  wall[0]-=wallSpeed;
}
void wallDrawer(int index)
{
  int[] wall = walls.get(index);
  int gapWallX = wall[0];
  int gapWallY = wall[1];
  int gapWallWidth = wall[2];
  int gapWallHeight = wall[3];
  rectMode(CORNER);
  fill(wallColors);
  rect(gapWallX, 0, gapWallWidth, gapWallY);
  rect(gapWallX, gapWallY+gapWallHeight,gapWallWidth,
      height-gapWallY-gapWallHeight);
}
void watchWallCollision(int index)
{
  int[] wall = walls.get(index);
  int gapWallX = wall[0];
  int gapWallY = wall[1];
  int gapWallWidth = wall[2];
  int gapWallHeight = wall[3];
  int wallTopX = gapWallX;
  int wallTopY = 0;
  int wallTopWidth = gapWallWidth;
  int wallTopHeight = gapWallY;
  int wallBottomX = gapWallX;
  int wallBottomY = gapWallY + gapWallHeight;
  int wallBottomWidth = gapWallWidth;
  int wallBottomHeight = height-gapWallY-gapWallHeight;

}