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

#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
#define OLED_RESET 4
#define SCREEN_ADDRESS 0x3D

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

const int buttonPin1 = 2;
const int buttonPin2 = 3;
const int buttonPin3 = 1;
volatile int buttonCode = 3;

void ISR_button1Pressed() {
  //buttonCode = 64;
  buttonCode++;
}

void ISR_button2Pressed() {
  buttonCode = 36;
}

void ISR_button3Pressed() {
  buttonCode = 3;
}

void setup() {
  Serial.begin(9600);
  pinMode(buttonPin1, INPUT_PULLUP);
  pinMode(buttonPin2, INPUT_PULLUP);
  pinMode(buttonPin3, INPUT_PULLUP);
  attachInterrupt(digitalPinToInterrupt(buttonPin1), ISR_button1Pressed, FALLING);
  attachInterrupt(digitalPinToInterrupt(buttonPin2), ISR_button2Pressed, FALLING);
  attachInterrupt(digitalPinToInterrupt(buttonPin3), ISR_button3Pressed, FALLING);
  display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
  display.clearDisplay();
  display.setTextSize(8);
  display.setTextColor(WHITE);
}

void loop() {
  display.clearDisplay();
  display.setCursor(0, 0);
  display.write(buttonCode);
  display.display();
  delay(100);
}