#include <LiquidCrystal.h>
#include <dht.h>

dht DHT;

#define DHT22_PIN 13

class Keyboard
{
private:
  int rows[4];
  int cols[4];

public:
  Keyboard(int, int, int, int, int, int, int, int);
  char keys();
  void begin();

};

Keyboard::Keyboard(int a, int b, int c, int d, int e, int f, int g, int h)
{
  rows[0] = a;
  rows[1] = b;
  rows[2] = c;
  rows[3] = d;
  cols[0] = e;
  cols[1] = f;
  cols[2] = g;
  cols[3] = h;
}

void Keyboard::begin()
{
  for(int i = 0; i < 4; i++)
  {
    pinMode(rows[i], INPUT_PULLUP);
    pinMode(cols[i], OUTPUT);
  }
}

char Keyboard::keys()
{
  char key_values[4][4] = {
                          {'1', '2', '3', '+'},
                          {'4', '5', '6', '-'},
                          {'7', '8', '9', '*'},
                          {'C', '0', '=', '/'}
                          };
  for(int j = 0; j < 4; j++)
  {
    for(int col = 0; col < 4; col++)
    {
      if(col == j)
      {
        digitalWrite(cols[j], LOW);
      }
      else
      {
        digitalWrite(cols[col], HIGH);
      }
    }
    for(int i = 0; i < 4; i++)
    {
      if(!digitalRead(rows[i]))
      {
        delay(200);
        return key_values[i][j];
      }
    }
  }

  return 10;
}

LiquidCrystal display(12, 11, 10, 9, 8, 7);
Keyboard kb(5, 4, 3, 2, A0, A1, A2, A3);
int s1 = 0, s2 = 0, ch1 = 0, ch2 = 0;
char c = 0;
String a1;

void setup()
{
  display.begin(20, 4);
  kb.begin();
}

void loop()
{
  char key = 0;
  key = kb.keys();
  switch(key)
  {
    case '1':
      display.setCursor(s1, s2);
      display.print(key);
      a1 += key;
      s1++;
      break;
    case '2':
      display.setCursor(s1, s2);
      display.print(key);
      a1 += key;
      s1++;
      break;
    case '3':
      display.setCursor(s1, s2);
      display.print(key);
      a1 += key;
      s1++;
      break;
    case '4':
      display.setCursor(s1, s2);
      display.print(key);
      a1 += key;
      s1++;
      break;
    case '5':
      display.setCursor(s1, s2);
      display.print(key);
      a1 += key;
      s1++;
      break;
    case '6':
      display.setCursor(s1, s2);
      display.print(key);
      a1 += key;
      s1++;
      break;
    case '7':
      display.setCursor(s1, s2);
      display.print(key);
      a1 += key;
      s1++;
      break;
    case '8':
      display.setCursor(s1, s2);
      display.print(key);
      a1 += key;
      s1++;
      break;
    case '9':
      display.setCursor(s1, s2);
      display.print(key);
      a1 += key;
      s1++;
      break;
    case '0':
      display.setCursor(s1, s2);
      display.print(key);
      a1 += key;
      s1++;
      break;
    case '+':
      display.setCursor(s1, s2);
      display.print(key);
      s1 = 0;
      s2 = !s2;
      c = '+';
      ch1 = a1.toInt();
      a1 = "";
      break;
    case '-':
      display.setCursor(s1, s2);
      display.print(key);
      s1 = 0;
      s2 = !s2;
      c = '-';
      ch1 = a1.toInt();
      a1 = "";
      break;
    case '*':
      display.setCursor(s1, s2);
      display.print(key);
      s1 = 0;
      s2 = !s2;
      c = '*';
      ch1 = a1.toInt();
      a1 = "";
      break;
    case '/':
      display.setCursor(s1, s2);
      display.print(key);
      s1 = 0;
      s2 = !s2;
      c = '/';
      ch1 = a1.toInt();
      a1 = "";
      break;
    case 'C':
      display.clear();
      display.setCursor(0, 0);
      s1 = s2 = 0;
      c = 0;
      ch1 = ch2 = 0;
      a1 = "";
      break;
    case '=':
      ch2 = a1.toInt();
      switch(c)
      {
        case '+':
          ch2 = ch1 + ch2;
          break;
        case '-':
          ch2 = ch1 - ch2;
          break;
        case '*':
          ch2 = ch1 * ch2;
          break;
        case '/':
          ch2 = ch1 / ch2;
          break;
      }
      display.clear();
      display.setCursor(0, 0);
      display.print(ch2);
      int chk = DHT.read22(DHT22_PIN);
      display.setCursor(0,2); 
      display.print("Temp: ");
      display.print(DHT.temperature);
      display.print((char)223);
      display.print("C");
      display.setCursor(0,3);
      display.print("Humidity: ");
      display.print(DHT.humidity);
      display.print("%");
      delay(1000);
      break;
  }

}