// https://forum.arduino.cc/t/ds3231-24-hours-time-format/981645

#include <Wire.h>
#include <DS3231.h>
#include "SSD1306Ascii.h"
#include "SSD1306AsciiWire.h"

// --------------

#define BTN_PIN 3
#define LED 12  
#define dspTime 5000

// 0X3C+SA0 - 0x3C or 0x3D
#define SSDI2C_ADDRESS 0x3C

// Define proper RST_PIN if required.
#define RST_PIN -1

// --------------

const int debounceDelay = 100; // milliseconds to wait until button input stable *

// --------------
 
int format = 24;
int hours;
int minutes;
int seconds;

bool h12Flag;
bool pmFlag;
  
bool oledMode;

// --------------

SSD1306AsciiWire oled;
DS3231 clk;

 
// --------------

void time_setup()
 
{  
  Serial.println(" ");
  Serial.println("DS3231 based Clock and Calender");
    
//Read the time from serial monitor and display entries
  Serial.print("Enter the hours : ");
  while(Serial.available() == 0) { }   
  hours = Serial.parseInt();
  Serial.println(hours);
    
  Serial.print("Enter the minutes : ");
  while(Serial.available() == 0) { }   
  minutes = Serial.parseInt();
  Serial.println(minutes);
    
  Serial.print("Enter the seconds : ");
  while(Serial.available() == 0) { }    
  seconds = Serial.parseInt();
  Serial.println(seconds); 
      
//Print the resulting time
  Serial.println("-------------------------------------------------------------");
  Serial.print("The RTC is set to : ");
  Serial.print(hours);
  Serial.print(" : ");
  Serial.print(minutes);
  Serial.print(" : ");
  Serial.println(seconds);  
  Serial.println("-------------------------------------------------------------");
  return;
}

// --------------

void RTC_setup()

{
  clk.setHour(hours);
  clk.setMinute(minutes);
  clk.setSecond(seconds);
  clk.setClockMode(false);   

  Serial.println("RTC has been set with the new time.");
  Serial.println("-------------------------------------------------------------");

  return;
}

// --------------

void RTC_oled()
 
{
  unsigned long startTime;

  startTime = millis();

  while (millis() <= (startTime + dspTime))
  {
    hours   = clk.getHour(h12Flag,pmFlag);
    minutes = clk.getMinute();
    seconds = clk.getSecond();

    oled.setCursor(1,1);

// display hours
    if(hours<10)
    {
      oled.print(" 0");
    }
    else
    {
      oled.print(" ");
    }
    oled.print(hours);
    oled.print(" : ");
    
// display minutes
    if(minutes<10)
    {
      oled.print("0");
    }
    oled.print(minutes);
    oled.print(" : ");
    
// display seconds
    if(seconds<10)
    {
      oled.print("0");
    }
    oled.print(seconds);

    if (oledMode == true)
    {
      oledMode = false;
      break;
    }

  }
  return;   
 }

// --------------

void wait(int waitTime)

{
	unsigned long startTime;

	startTime = millis();

	while (millis() < (startTime + waitTime))
	{
	}
	// do nothing

	return;
}

// --------------

boolean debounce(int pin) // debounce returns true if the switch in the given pin is closed and stable

{
  boolean state;
  boolean previousState;
  previousState = digitalRead(pin); // store switch state
  for (int counter = 0; counter < debounceDelay; counter++)
  {
    delay(1); // wait for 1 millisecond
    state = digitalRead(pin); // read the pin
    if ( state != previousState)
    {
      counter = 0; // reset the counter if the state changes
      previousState = state; // and save the current state
    }
  }
  // here when the switch state has been stable longer than the debounce period
  return state;
}

// --------------

void buttonPushed() // detect and debounce button push using assigned interrupt *

{ 	
  if (debounce(BTN_PIN))  // calls debounce procedure *
    {
//      digitalWrite(LED, HIGH); // Turn the button-LED on for feedback
      oledMode = true;
//      Serial.println(oledMode);
    }
//    delay(1000); 
//  digitalWrite(LED, LOW); // Turn the button-LED off
  return;
}

// --------------

void setup()

{  
  pinMode(BTN_PIN, INPUT_PULLUP);
  pinMode(LED, OUTPUT);

  attachInterrupt(digitalPinToInterrupt(BTN_PIN), buttonPushed, FALLING); // assign interrupt to button, procedure to be run and set state to LOW when pushed *

  Serial.begin(115200);

  Wire.begin();
//  Wire.setClock(400000L);

#if RST_PIN >= 0
  oled.begin(&Adafruit128x64, SSDI2C_ADDRESS, RST_PIN);
#else // RST_PIN >= 0
  oled.begin(&Adafruit128x64, SSDI2C_ADDRESS);
#endif // RST_PIN >= 0

  oled.clear();
  oled.setFont(Verdana12);
  oledMode = false;  

  time_setup();
  RTC_setup();
}

// --------------

void loop()

{
  if (oledMode == true)
  {
    oledMode = false;
    RTC_oled();
    oled.clear();
  }
}