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

RTC_DS1307 rtc;

#define LED 8
#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
#define OLED_RESET 4
#define SCREEN_ADDRESS 0x3C

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

unsigned long old_time = 0;

void setup() {
  Serial.begin(9600);
  pinMode(LED, OUTPUT);

  if (!display.begin(SSD1306_SWITCHCAPVCC, SCREEN_ADDRESS)) {
    while (true);
  }

  if (!rtc.begin()) {
    while (true) delay(10);
  }

  rtc.adjust(DateTime(F(__DATE__), F(__TIME__)));

  display.clearDisplay();
  showStr("NKHS", 41, 0, 1);
  showStr("C241", 41, 16, 1);
  display.display();
  delay(2000);
  old_time = millis();
}

void loop() {
  String years, months, days, hours, minutes, seconds, date, time;
  DateTime now = rtc.now();

  CPU();

  years = fixtime(String(now.year()));
  months = fixtime(String(now.month()));
  days = fixtime(String(now.day()));
  hours = fixtime(String(now.hour()));
  minutes = fixtime(String(now.minute()));
  seconds = fixtime(String(now.second()));

  date = years + "/" + months + "/" + days;
  time = hours + ":" + minutes + ":" + seconds;

  display.clearDisplay();
  showStr(date, 5, 0, 1);
  showStr(time, 16, 32, 1);
  display.display();

  delay(1000);
}

void CPU() {
  if (millis() - old_time > 1000) {
    old_time = millis();
    digitalWrite(LED, !digitalRead(LED));
  }
}

void showStr(String s, int x, int y, int color) {
  display.setTextSize(2);
  display.setTextColor(color == 1 ? SSD1306_WHITE : SSD1306_BLACK);
  display.setCursor(x, y);
  display.println(s);
}

String fixtime(String s) {
  if (s.length() == 1) return "0" + s;
  else return s;
}