#include <Wire.h>
#include <LiquidCrystal_I2C.h>
#include <Time.h>
#include <TimeLib.h>
#include <DS1302RTC.h>

#define RST 2 // RST or CE
#define DAT 3 // DAT or IO
#define CLK 4 // CLK

LiquidCrystal_I2C lcd(0x3F, 16, 2);

DS1302RTC RTC(RST, DAT, CLK);
tmElements_t tm;

const char days[7][4] = {"MON", "TUE", "WED", "THU", "FRI", "SAT", "SUN"};

void setup() {
    lcd.init(); // initialize the lcd
    lcd.backlight(); // turn on backlight
    Serial.begin(9600);

    setDateTime();

    if (RTC.haltRTC()) {
        Serial.println("The DS1302 is stopped. Please run the SetTime");
        Serial.println("example to initialize the time and begin running.");
        Serial.println();
    }
    if (!RTC.writeEN()) {
        Serial.println("The DS1302 is write protected. This normal.");
        Serial.println();
    }
}

unsigned long prevSec = 0;

void loop() {
    unsigned long nowSec = millis() / 1000;
    if (prevSec != nowSec) { 
        RTC.read(tm);
        outputDateTime();
        prevSec = nowSec;
    }
}

void outputDateTime() {
    char dateStr[20];
    char timeStr[20];
    
    sprintf(dateStr, "%4d-%02d-%02d %s", tmYearToCalendar(tm.Year), tm.Month, tm.Day, days[tm.Wday-2]);
    sprintf(timeStr, "%s %02d:%02d:%02d", getCurrentAm(tm.Hour), getCurrentHour(tm.Hour), tm.Minute, tm.Second);
    
    lcd.setCursor(0, 0);
    lcd.print(dateStr);
    lcd.setCursor(1, 1);
    lcd.print(timeStr);
}

bool isAm(int hour){
  return hour-12 < 0;
}

int getCurrentHour(int hour){
  return isAm(hour) ? hour : hour-12;
}

char* getCurrentAm(int hour){
  return isAm(hour) ? "AM" : "PM";
}

void setDateTime() {
    time_t t;
    tm.Year = CalendarYrToTm(2017);
    tm.Month = 5;
    tm.Day = 31;
    tm.Hour = 14;
    tm.Minute = 41;
    tm.Second = 55;
    t = makeTime(tm);
    if (RTC.set(t) == 0) { // Success
        setTime(t);
    } else
        Serial.println("RTC set failed!");
}