/*
 * ESP32 Ping Pong Game
 * Display: 0.96" OLED (SSD1306, 128x64, I2C)
 *
 * Wiring:
 *   OLED SDA  -> GPIO 21
 *   OLED SCL  -> GPIO 22
 *   OLED VCC  -> 3.3V
 *   OLED GND  -> GND
 *
 *   LEFT  Button -> GPIO 12 (other leg to GND)
 *   RIGHT Button -> GPIO 14 (other leg to GND)
 *   START Button -> GPIO 27 (other leg to GND, also used to restart after game over)
 *
 * Libraries required (install via Arduino Library Manager):
 *   - Adafruit SSD1306
 *   - Adafruit GFX Library
 */

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

// ── Display config ──────────────────────────────────────────────────────────
#define SCREEN_WIDTH  128
#define SCREEN_HEIGHT  64
#define OLED_RESET     -1          // not used with I2C
#define SCREEN_ADDRESS 0x3C        // most common SSD1306 address

Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);

// ── Button pins ─────────────────────────────────────────────────────────────
#define BTN_LEFT   12
#define BTN_RIGHT  14
#define BTN_START  27

// ── Game dimensions ─────────────────────────────────────────────────────────
#define PADDLE_W   24
#define PADDLE_H    4
#define PADDLE_Y   (SCREEN_HEIGHT - 6)   // y position of paddle top edge
#define PADDLE_SPEED 3

#define BALL_SIZE   3
#define SCORE_AREA  10   // pixels reserved at top for score bar

// ── Game state ───────────────────────────────────────────────────────────────
float  ballX, ballY;
float  ballDX, ballDY;
int    paddleX;
int    score;
bool   gameOver;
bool   gameStarted;

// Debounce helpers
unsigned long lastLeft  = 0;
unsigned long lastRight = 0;
unsigned long lastStart = 0;
#define DEBOUNCE_MS 50

// ── Helpers ──────────────────────────────────────────────────────────────────
bool btnPressed(int pin, unsigned long &lastTime) {
  if (digitalRead(pin) == LOW) {
    unsigned long now = millis();
    if (now - lastTime > DEBOUNCE_MS) {
      lastTime = now;
      return true;
    }
  }
  return false;
}

void initGame() {
  paddleX = (SCREEN_WIDTH - PADDLE_W) / 2;

  // Ball starts just above paddle centre
  ballX  = SCREEN_WIDTH  / 2.0f;
  ballY  = PADDLE_Y - BALL_SIZE - 2;

  // Random horizontal direction, always going upward first
  float angle = radians(random(210, 330));   // 210–330° → upward arc
  float speed = 2.2f;
  ballDX = cos(angle) * speed;
  ballDY = sin(angle) * speed;

  score    = 0;
  gameOver = false;
}

// ── Setup ────────────────────────────────────────────────────────────────────
void setup() {
  Serial.begin(115200);

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

  randomSeed(analogRead(0));

  if (!display.begin(SSD1306_SWITCHCAPVCC, SCREEN_ADDRESS)) {
    Serial.println(F("SSD1306 allocation failed"));
    for (;;);
  }
  display.clearDisplay();
  display.setTextColor(SSD1306_WHITE);

  gameStarted = false;
  gameOver    = false;
  score       = 0;

  showTitleScreen();
}

// ── Title screen ─────────────────────────────────────────────────────────────
void showTitleScreen() {
  display.clearDisplay();
  display.setTextSize(2);
  display.setCursor(14, 10);
  display.print(F("PONG"));

  display.setTextSize(1);
  display.setCursor(10, 36);
  display.print(F("Press START"));
  display.setCursor(16, 48);
  display.print(F("to begin!"));

  display.display();
}

// ── Game-over screen ─────────────────────────────────────────────────────────
void showGameOver() {
  display.clearDisplay();
  display.setTextSize(2);
  display.setCursor(4, 6);
  display.print(F("GAME OVR"));

  display.setTextSize(1);
  display.setCursor(28, 30);
  display.print(F("Score: "));
  display.print(score);

  display.setCursor(10, 46);
  display.print(F("Press START"));
  display.setCursor(22, 56);
  display.print(F("to retry"));

  display.display();
}

// ── Main loop ────────────────────────────────────────────────────────────────
void loop() {
  // ── Wait for start ────────────────────────────────────────────────────────
  if (!gameStarted) {
    if (btnPressed(BTN_START, lastStart)) {
      gameStarted = true;
      initGame();
    }
    return;
  }

  // ── Game-over state ───────────────────────────────────────────────────────
  if (gameOver) {
    if (btnPressed(BTN_START, lastStart)) {
      initGame();
    }
    return;
  }

  // ── Read paddle input ─────────────────────────────────────────────────────
  if (digitalRead(BTN_LEFT) == LOW) {
    paddleX -= PADDLE_SPEED;
    if (paddleX < 0) paddleX = 0;
  }
  if (digitalRead(BTN_RIGHT) == LOW) {
    paddleX += PADDLE_SPEED;
    if (paddleX > SCREEN_WIDTH - PADDLE_W) paddleX = SCREEN_WIDTH - PADDLE_W;
  }

  // ── Move ball ─────────────────────────────────────────────────────────────
  ballX += ballDX;
  ballY += ballDY;

  // Wall bounces (left / right)
  if (ballX <= 0) {
    ballX  = 0;
    ballDX = -ballDX;
  } else if (ballX + BALL_SIZE >= SCREEN_WIDTH) {
    ballX  = SCREEN_WIDTH - BALL_SIZE;
    ballDX = -ballDX;
  }

  // Top wall bounce
  if (ballY <= SCORE_AREA) {
    ballY  = SCORE_AREA;
    ballDY = -ballDY;
  }

  // Paddle collision
  if (ballY + BALL_SIZE >= PADDLE_Y &&
      ballY + BALL_SIZE <= PADDLE_Y + PADDLE_H + 2 &&
      ballX + BALL_SIZE >= paddleX &&
      ballX             <= paddleX + PADDLE_W) {

    ballY  = PADDLE_Y - BALL_SIZE;      // push ball above paddle
    ballDY = -ballDY;                   // reverse vertical

    // Add a little spin based on where ball hits paddle
    float hitPos = (ballX + BALL_SIZE / 2.0f) - (paddleX + PADDLE_W / 2.0f);
    ballDX += hitPos * 0.06f;

    // Clamp speed so it doesn't get out of hand
    float speed = sqrt(ballDX * ballDX + ballDY * ballDY);
    if (speed > 4.5f) {
      ballDX = ballDX / speed * 4.5f;
      ballDY = ballDY / speed * 4.5f;
    }

    score++;
  }

  // Missed ball → game over
  if (ballY > SCREEN_HEIGHT) {
    gameOver = true;
    showGameOver();
    return;
  }

  // ── Draw frame ────────────────────────────────────────────────────────────
  display.clearDisplay();

  // Score bar
  display.setTextSize(1);
  display.setCursor(0, 0);
  display.print(F("Score:"));
  display.print(score);

  // Divider line under score
  display.drawLine(0, SCORE_AREA - 1, SCREEN_WIDTH - 1, SCORE_AREA - 1, SSD1306_WHITE);

  // Ball
  display.fillRect((int)ballX, (int)ballY, BALL_SIZE, BALL_SIZE, SSD1306_WHITE);

  // Paddle
  display.fillRect(paddleX, PADDLE_Y, PADDLE_W, PADDLE_H, SSD1306_WHITE);

  display.display();

  delay(16);   // ~60 fps target
}