#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64

Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, -1);

#define BTN_LEFT 2
#define BTN_RIGHT 3

int paddleX = 54;
int paddleWidth = 20;

int ballX = 64;
int ballY = 30;
int ballDX = 2;
int ballDY = -2;

void setup() {

  pinMode(BTN_LEFT, INPUT_PULLUP);
  pinMode(BTN_RIGHT, INPUT_PULLUP);

  display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
  display.clearDisplay();
}

void loop() {

  if(!digitalRead(BTN_LEFT)) paddleX -= 3;
  if(!digitalRead(BTN_RIGHT)) paddleX += 3;

  if(paddleX < 0) paddleX = 0;
  if(paddleX > 108) paddleX = 108;

  ballX += ballDX;
  ballY += ballDY;

  if(ballX <= 0 || ballX >= 128) ballDX = -ballDX;
  if(ballY <= 0) ballDY = -ballDY;

  if(ballY >= 58 && ballX > paddleX && ballX < paddleX + paddleWidth) {
    ballDY = -ballDY;
  }

  if(ballY > 64) {
    ballX = 64;
    ballY = 30;
  }

  display.clearDisplay();

  display.fillRect(paddleX,60,paddleWidth,3,WHITE);
  display.fillCircle(ballX,ballY,2,WHITE);

  display.display();

  delay(20);
}