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

#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
#define OLED_RESET -1

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

// =====================
// CONFIG BUTTON
// =====================
#define BTN_UP     2
#define BTN_DOWN   14
#define BTN_LEFT   13
#define BTN_RIGHT  4

// =====================
// ENGINE CORE
// =====================
unsigned long lastTime;
float deltaTime;

void Engine_Init() {
  lastTime = millis();
}

void Engine_Update() {
  unsigned long now = millis();
  deltaTime = (now - lastTime) / 1000.0;
  lastTime = now;
}

// =====================
// INPUT SYSTEM
// =====================
bool inputUp, inputDown, inputLeft, inputRight;

void Input_Update() {
  inputUp    = !digitalRead(BTN_UP);
  inputDown  = !digitalRead(BTN_DOWN);
  inputLeft  = !digitalRead(BTN_LEFT);
  inputRight = !digitalRead(BTN_RIGHT);
}

// =====================
// GAME DATA
// =====================
int playerX = 64;
int playerY = 32;
int speed = 60; // pixel per second

// =====================
// GAME LOGIC
// =====================
void Game_Update() {

  if (inputUp)    playerY -= speed * deltaTime;
  if (inputDown)  playerY += speed * deltaTime;
  if (inputLeft)  playerX -= speed * deltaTime;
  if (inputRight) playerX += speed * deltaTime;

  // Boundary check
  if (playerX < 0) playerX = 0;
  if (playerX > SCREEN_WIDTH-1) playerX = SCREEN_WIDTH-1;
  if (playerY < 0) playerY = 0;
  if (playerY > SCREEN_HEIGHT-1) playerY = SCREEN_HEIGHT-1;
}

// =====================
// RENDER SYSTEM
// =====================
void Game_Render() {
  display.clearDisplay();
  display.drawPixel(playerX, playerY, WHITE);
  display.display();
}

// =====================
// SETUP & LOOP
// =====================
void setup() {

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

  if (!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {
    while(true); // OLED gagal
  }

  Engine_Init();
}

void loop() {

  Engine_Update();
  Input_Update();
  Game_Update();
  Game_Render();
}