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

#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64 
#define buttonPin 2

Adafruit_SSD1306 oled(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, -1);
RTC_DS1307 rtc;

String displayTime;
DateTime timerStart;
int mode = 0;
int hour, minute, second, pauseSecond;
bool timerToggle = false;
bool buttonPressed = false;

void setup() {
  Serial.begin(9600);

  pinMode(buttonPin, INPUT_PULLUP);
  attachInterrupt(0, buttonPress, FALLING);

  if (!oled.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {
    Serial.println(F("SSD1306 allocation failed"));
    while (true);
  }

  delay(1000);         
  oled.clearDisplay();

  oled.setTextSize(1);         
  oled.setTextColor(WHITE);     
  oled.setCursor(0, 10);        

  if (! rtc.begin()) {
    Serial.println("Couldn't find RTC");
    Serial.flush();
    while (true);
  }

  rtc.adjust(DateTime(F(__DATE__), F(__TIME__)));
  timerStart = rtc.now();
  
  Serial.println("----Serial Open----\n");
  Serial.println("Clock/Timer Instructions : ");
  Serial.println("    -- Hold Button for >1s to change mode");
  Serial.println("    -- Short press to start/stop timer\n");

}

void loop() {

  if (buttonPressed) {
    int count = 0;
    bool buttonState = 0;

    Serial.println("(Start Press)");

    while (!buttonState){
      count += 1;
      buttonState = digitalRead(buttonPin);
      delay(20);
    }

    float duration = count*20.00/1000;
    Serial.print("(End press. Press time: ");
    Serial.print(duration);
    Serial.println(" s)");
    if (count >= 50){
      timerToggle = false;
      changeMode();
    }

    else if (count < 50 && mode == 1) {
      pauseTimer();
      if (timerToggle) { Serial.println(">> Timer Start"); }
      else { Serial.println(">> Timer Pause"); }
    }

    else { Serial.println(">> Cannot stop time... :(");}
   
    delay(200);
    interrupts();
    buttonPressed = false;
  }

  displayTime = getTime(mode);
  oledDisplayCenter(displayTime);

}

//Function to display text in centre of OLED
void oledDisplayCenter(String text) {
  int16_t x1;
  int16_t y1;
  uint16_t width;
  uint16_t height;

  oled.getTextBounds(text, 0, 0, &x1, &y1, &width, &height);

  
  oled.clearDisplay(); 
  oled.setCursor((SCREEN_WIDTH - width) / 2, (SCREEN_HEIGHT - height) / 2);
  oled.println(text); 
  oled.display();

}

//Function to register interrupt button press
void buttonPress(){

  buttonPressed = true;
  delay(20);
  //Stops interrupts to prevent interference during hold
  noInterrupts();
  
}

//Function to calculate and return time/timer output as String
String getTime(int mode){

  DateTime now = rtc.now();
  String time;

  //Change output depending on mode setting. 0 = Clock, 1 = Timer
  switch (mode) {
    case 0:
      hour = now.hour();
      minute = now.minute();
      second = now.second();
      break;
    case 1:
      //Calculate seconds passed since timer started (timerToggle = true)
      if (timerToggle){
        second = now.second()-timerStart.second()+pauseSecond;
        //Add to minutes at 60 seconds, reset seconds
        if (second < 0) { second += 60; }
        if (second > 59) {
          timerStart = rtc.now(); 
          pauseSecond = 0;
          minute += 1; 
        }
        //Add to hours at 60 minutes, reset minutes
        if (minute < 0) { minute += 60; }
        if (minute > 59) {
          minute = 0;
          hour += 1;
        }
      }
      //If paused (timerToggle = false), do nothing
      else if (!timerToggle){
        break;
      }
      break;
  }

  //Create string from time values
  time = "";
  time += hour;
  time += ':';
  time += minute;
  time += ':';
  time += second;

  return time;
}

//Function to iterate through modes
void changeMode() {
  mode += 1;
  if (mode > 1) { mode = 0; }
  delay(50);
  if (mode == 0 ){
    oledDisplayCenter("Mode Changed: Clock");
    Serial.println("Mode Changed: Clock");
  }
  if (mode == 1 ){
    oledDisplayCenter("Mode Changed: Timer");
    Serial.println("Mode Changed: Timer");
  }
  delay(100);
  resetTimer();
}

//Function to pause timer
void pauseTimer() {
  if (timerToggle) { 
    pauseSecond = second;
    timerToggle = false; 
  }
  else { timerToggle = true; }
  timerStart = rtc.now();
}

//Function to reset timer
void resetTimer() {
  hour = 0;
  minute = 0;
  second = 0;
  pauseSecond = 0;
}