#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);

// Botones
const int btnVolver = 25;
const int btnArriba = 26;
const int btnAbajo = 27;
const int btnSeleccionar = 14;

// Menú principal
const char* menuItems[] = {"Calc", "Dev"};
int menuLength = sizeof(menuItems)/sizeof(menuItems[0]);
int currentSelection = 0;

// Estado de pantalla
enum Screen { MENU, CALC, DEV };
Screen currentScreen = MENU;

// Texto para Dev
const char* devText[] = {
  "ESP32 NodeMCU-32S:",
  "WiFi + Bluetooth",
  "Consumo ultra bajo",
  "Microcontrolador dual-core",
  "Compatible con Arduino IDE",
  "Admite deep sleep",
  "Ideal IoT y proyectos embebidos",
  "OLED 128x64 con I2C"
};
int devLines = sizeof(devText)/sizeof(devText[0]);
int devScroll = 0;

// Calculadora
String input1 = "";
String input2 = "";
char oper = '\0';
bool enteringSecond = false;

void setup() {
  Serial.begin(115200);

  if(!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {
    Serial.println(F("Fallo al iniciar pantalla OLED"));
    for(;;);
  }

  pinMode(btnVolver, INPUT_PULLUP);
  pinMode(btnArriba, INPUT_PULLUP);
  pinMode(btnAbajo, INPUT_PULLUP);
  pinMode(btnSeleccionar, INPUT_PULLUP);

  drawMenu();
}

void loop() {
  // Botón Arriba
  if(digitalRead(btnArriba) == LOW){
    if(currentScreen == MENU){
      currentSelection--;
      if(currentSelection < 0) currentSelection = menuLength - 1;
      drawMenu();
    } else if(currentScreen == DEV){
      if(devScroll > 0) devScroll--;
      drawDev();
    } else if(currentScreen == CALC){
      incrementCurrent();
      drawCalc();
    }
    delay(150);
  }

  // Botón Abajo
  if(digitalRead(btnAbajo) == LOW){
    if(currentScreen == MENU){
      currentSelection++;
      if(currentSelection >= menuLength) currentSelection = 0;
      drawMenu();
    } else if(currentScreen == DEV){
      if(devScroll < devLines - 4) devScroll++;
      drawDev();
    } else if(currentScreen == CALC){
      decrementCurrent();
      drawCalc();
    }
    delay(150);
  }

  // Botón Volver
  if(digitalRead(btnVolver) == LOW){
    if(currentScreen == CALC){
      input1 = "";
      input2 = "";
      oper = '\0';
      enteringSecond = false;
      drawCalc();
    } else {
      currentScreen = MENU;
      drawMenu();
    }
    delay(150);
  }

  // Botón Seleccionar
  if(digitalRead(btnSeleccionar) == LOW){
    if(currentScreen == MENU){
      if(currentSelection == 0){ // Calc
        currentScreen = CALC;
        input1 = "";
        input2 = "";
        oper = '\0';
        enteringSecond = false;
        drawCalc();
      } else if(currentSelection == 1){ // Dev
        currentScreen = DEV;
        devScroll = 0;
        drawDev();
      }
    } else if(currentScreen == CALC){
      handleCalcSelect();
    }
    delay(150);
  }
}

// ------------------- DIBUJOS -------------------
void drawMenu(){
  display.clearDisplay();
  display.setTextSize(1);
  for(int i=0; i<menuLength; i++){
    if(i == currentSelection)
      display.setTextColor(SSD1306_BLACK, SSD1306_WHITE);
    else
      display.setTextColor(SSD1306_WHITE);
    display.setCursor(0, i*10);
    display.println(menuItems[i]);
  }
  display.display();
}

void drawDev(){
  display.clearDisplay();
  display.setTextSize(1);
  display.setTextColor(SSD1306_WHITE);
  for(int i=0; i<4; i++){
    int idx = i + devScroll;
    if(idx < devLines){
      display.setCursor(0, i*12);
      display.println(devText[idx]);
    }
  }
  display.display();
}

void drawCalc(){
  display.clearDisplay();
  display.setTextSize(1);
  display.setTextColor(SSD1306_WHITE);
  display.setCursor(0,0);
  display.print("Calc:");
  display.setCursor(0,12);
  display.print(input1);
  if(oper != '\0') display.print(oper);
  if(enteringSecond) display.print(input2);
  display.display();
}

// ------------------- CALCULADORA -------------------
void handleCalcSelect(){
  if(!enteringSecond){
    if(input1.length() == 0) input1 = "0";
    oper = '+';
    enteringSecond = true;
  } else if(input2.length() == 0){
    input2 = "0";
  } else {
    // Calcular
    float n1 = input1.toFloat();
    float n2 = input2.toFloat();
    float result = 0;

    switch(oper){
      case '+': result = n1 + n2; break;
      case '-': result = n1 - n2; break;
      case '*': result = n1 * n2; break;
      case '/': result = n2 != 0 ? n1 / n2 : 0; break;
    }

    input1 = String(result);
    input2 = "";
    oper = '\0';
    enteringSecond = false;
  }
  drawCalc();
}

// Cambia el dígito actual en input1 o input2
void incrementCurrent(){
  if(!enteringSecond){
    if(input1.length() == 0) input1 = "0";
    int val = input1.toInt();
    val = (val + 1) % 1000; // máximo 999
    input1 = String(val);
  } else {
    if(input2.length() == 0) input2 = "0";
    int val = input2.toInt();
    val = (val + 1) % 1000;
    input2 = String(val);
  }
}

void decrementCurrent(){
  if(!enteringSecond){
    if(input1.length() == 0) input1 = "0";
    int val = input1.toInt();
    val = (val - 1 + 1000) % 1000;
    input1 = String(val);
  } else {
    if(input2.length() == 0) input2 = "0";
    int val = input2.toInt();
    val = (val - 1 + 1000) % 1000;
    input2 = String(val);
  }
}