#include "Wire.h"
#include "LiquidCrystal_I2C.h"
LiquidCrystal_I2C LCD(0x27, 16, 2);

boolean button1WasUp = true;
boolean button2WasUp = true;
boolean button3WasUp = true;
boolean button4WasUp = true;

byte w = 0;

int SEC = 0;
int MIN = 0;
unsigned long timer;

void setup() {
   pinMode(2, INPUT_PULLUP);
   pinMode(4, INPUT_PULLUP);
   pinMode(6, INPUT_PULLUP);
   pinMode(8, INPUT_PULLUP);

   pinMode(10, OUTPUT);
   pinMode(12, OUTPUT);
   digitalWrite(10, HIGH);

   LCD.init();
   LCD.backlight(); 

   LCD.setCursor(2, 0);
   LCD.print("TIMER  STOP");
   LCD.setCursor(5, 1);
   LCD.print(MIN);
   LCD.print(" : ");
   LCD.print(SEC);
}

void loop() {
   boolean button1IsUp = digitalRead(2);
   boolean button2IsUp = digitalRead(4);
   boolean button3IsUp = digitalRead(6);
   boolean button4IsUp = digitalRead(8);

    if (button1WasUp && !button1IsUp) {
      delay(10);
      button1IsUp = digitalRead(2);
      if (!button1IsUp) {
         MIN = MIN - 1; SEC = 0;
         if (MIN < 0) { MIN = 0; }
         LCD.clear(); 
         LCD.setCursor(2, 0); 
         LCD.print("TIMER STOP"); 
         LCD.setCursor(5, 1); 
         LCD.print(MIN); 
         LCD.print(" : "); 
         LCD.print(SEC);
      }
   } 
   button1WasUp = button1IsUp;
   
   if (button2WasUp && !button2IsUp) {
      delay(10); 
      button2IsUp = digitalRead(4); 
      if (!button2IsUp) { 
         MIN = MIN + 1; SEC = 0; 
         LCD.clear(); 
         LCD.setCursor(2, 0); 
         LCD.print("TIMER STOP"); 
         LCD.setCursor(5, 1); 
         LCD.print(MIN); 
         LCD.print(" : "); 
         LCD.print(SEC);
      }
   } 
   button2WasUp = button2IsUp;

   if (button3WasUp && !button3IsUp && MIN > 0) {
      delay(10);
      button3IsUp = digitalRead(6);
      if (!button3IsUp) {
         if (SEC == 0) { SEC = 60; MIN = MIN - 1; }
         if (MIN < 0 ) { MIN = 0; }
         digitalWrite(10, LOW);
         w = 1;
      }
   }
   button3WasUp = button3IsUp;

   if (button4WasUp && !button4IsUp) {
      delay(10);
      button4IsUp = digitalRead(8);
      if (!button4IsUp) {
         MIN = 0; SEC = 0;
         digitalWrite(10, HIGH);
         LCD.clear();
         LCD.setCursor(2, 0);
         LCD.print("TIMER STOP");
         LCD.setCursor(5, 1);
         LCD.print(MIN);
         LCD.print(" : ");
         LCD.print(SEC);
      }
   }
   button4WasUp = button4IsUp;

   while (w == 1 ) {
      if (millis() - timer > 995) {
         timer = millis();
         SEC = SEC - 1;

         if (SEC == 0 && MIN == 0) {
            LCD.clear();
            LCD.setCursor(2, 0);
            LCD.print("TIMER  STOP");
            LCD.setCursor(5, 1);
            LCD.print(MIN);
            LCD.print(" : ");
            LCD.print(SEC);
            digitalWrite(10, HIGH);
            tone(12, 100);
            delay(500);
            noTone(12);
            w = 0;
         }

         if (SEC == 0) {
            SEC = 59; MIN = MIN - 1;
            if (MIN < 0 ) { MIN = 0; }
         }

         if (w == 1) {
            LCD.clear();
            LCD.setCursor(2, 0);
            LCD.print("TIMER START");
            LCD.setCursor(5, 1);
            LCD.print(MIN);
            LCD.print(" : ");
            LCD.print(SEC);
         }
     }
 
     boolean button3IsUp = digitalRead(6);
     if (button3WasUp && !button3IsUp) {
        delay(10);
        button3IsUp = digitalRead(6);
        if (!button3IsUp) {
           LCD.setCursor(2, 0);
           LCD.print("TIMER  STOP");
           w = 0;
        }
     }
     button3WasUp = button3IsUp; 
   }
}