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

#define SCREEN_WIDTH 128 // OLED display width,  in pixels
#define SCREEN_HEIGHT 64 // OLED display height, in pixels

Adafruit_SSD1306 oled(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, -1); // // create SSD1306 display object connected to I2C
RTC_DS3231 rtc;

String time;

void setup() {
  Serial.begin(9600);
  // initialize OLED display with address 0x3C for 128x64

  if(!oled.begin(SSD1306_SWITCHCAPVCC, 0x3C)) { // Address 0x3D for 128x64
    Serial.println(F("SSD1306 allocation failed"));
    for(;;); // Don't proceed, loop forever
  }
  delay(2000);         // wait for initializing
  oled.clearDisplay(); // clear display
  oled.setTextSize(1);          // text size
  oled.setTextColor(WHITE);     // text color
  oled.setCursor(0, 5);        // position to display

  // SETUP RTC MODULE
  if (!rtc.begin()) {
    Serial.println("Couldn't find RTC");
    Serial.flush();
    for(;;);
  }

  // automatically sets the RTC to the date & time on PC this sketch was compiled
  rtc.adjust(DateTime(F(__DATE__), F(__TIME__)));
  time.reserve(10); // to avoid fragmenting memory when using String
}

void Display(String text) {
  int16_t x;
  int16_t y;
  uint16_t WIDTH;
  uint16_t HEIGHT;

  oled.getTextBounds(text, 0, 0, &x, &y, &WIDTH, &HEIGHT);

  // display on horizontal and vertical center
  oled.clearDisplay(); // clear display
  oled.setCursor((SCREEN_WIDTH - WIDTH) / 2, (SCREEN_HEIGHT - HEIGHT) / 2);
  oled.println(text); // text to display
  oled.display();
}

void loop() {
  DateTime now = rtc.now();

  time = "";
  time += now.hour();
  time += ':';
  time += now.minute();
  time += ':';
  time += now.second();

  Display(time);
}