// Define segment pins
#define SEG_A 6
#define SEG_B 7
#define SEG_C 8
#define SEG_D 9
#define SEG_E 10
#define SEG_F 11
#define SEG_G 12

// Define digit pins
#define DIGIT_1 2
#define DIGIT_2 3
#define DIGIT_3 4
#define DIGIT_4 5

// Define keypad rows and cols
const int ROWS = 4;
const int COLS = 4;
char keys[ROWS][COLS] = {
  {'1', '2', '3', 'A'},
  {'4', '5', '6', 'B'},
  {'7', '8', '9', 'C'},
  {'*', '0', '#', 'D'}
};

// Define pin arrays for keypad
int rowPins[ROWS] = {14, 15, 16, 17};
int colPins[COLS] = {21, 20, 19, 18};

// Define variables for display
int digitPins[] = {DIGIT_1, DIGIT_2, DIGIT_3, DIGIT_4};
int displayValue[] = {0, 0, 0, 0};

void setup() {
  // Set up segment pins as outputs
  pinMode(SEG_A, OUTPUT);
  pinMode(SEG_B, OUTPUT);
  pinMode(SEG_C, OUTPUT);
  pinMode(SEG_D, OUTPUT);
  pinMode(SEG_E, OUTPUT);
  pinMode(SEG_F, OUTPUT);
  pinMode(SEG_G, OUTPUT);

  // Set up digit pins as outputs
  pinMode(DIGIT_1, OUTPUT);
  pinMode(DIGIT_2, OUTPUT);
  pinMode(DIGIT_3, OUTPUT);
  pinMode(DIGIT_4, OUTPUT);

  // Set up keypad pins as inputs with pull-up resistors
  for (int i = 0; i < ROWS; i++) {
    pinMode(rowPins[i], OUTPUT);
    digitalWrite(rowPins[i], HIGH);
  }
  for (int i = 0; i < COLS; i++) {
    pinMode(colPins[i], INPUT_PULLUP);
  }
}

void loop() {
  // Scan keypad for input
  char key = getKey();
  
  // Update display value if key is pressed
  if (key) {
    // Shift display value to the left
    for (int i = 3; i > 0; i--) {
      displayValue[i] = displayValue[i-1];
    }
    // Update first digit with new value
    displayValue[0] = key - '0';
  }
  
  // Display value on the segment display
  for (int i = 0; i < 4; i++) {
    digitalWrite(digitPins[i], LOW);
    displayDigit(displayValue[i]);
    delay(1);
    digitalWrite(digitPins[i], HIGH);
  }
}

char getKey() {
  char key = '\0';
  
  // Scan keypad for input
  for (int r = 0; r < ROWS; r++) {
    digitalWrite(rowPins[r], LOW);
    for (int c = 0; c < COLS; c++) {
      if (digitalRead(colPins[c]) == LOW) {
        key = keys[r][c];
      }
    }
    digitalWrite(rowPins[r], HIGH);
  }
  
  return key;
}

void displayDigit(int digit) {
  switch (digit) {
    case 0:
      digitalWrite(SEG_A, HIGH);
      digitalWrite(SEG_B, HIGH);
      digitalWrite(SEG_C, HIGH);
      digitalWrite(SEG_D, HIGH);
      digitalWrite(SEG_E, HIGH);
      digitalWrite(SEG_F, HIGH);
      digitalWrite(SEG_G, LOW);
      break;
    case 1:
      digitalWrite(SEG_A, HIGH);
      digitalWrite(SEG_B, LOW);
      digitalWrite(SEG_C, LOW);
      digitalWrite(SEG_D, HIGH);
      digitalWrite(SEG_E, HIGH);
      digitalWrite(SEG_F, HIGH);
      digitalWrite(SEG_G, HIGH);
      break;
    case 2:
      digitalWrite(SEG_A, HIGH);
      digitalWrite(SEG_B, HIGH);
      digitalWrite(SEG_C, LOW);
      digitalWrite(SEG_D, HIGH);
      digitalWrite(SEG_E, HIGH);
      digitalWrite(SEG_F, LOW);
      digitalWrite(SEG_G, HIGH);
      break;
    case 3:
      digitalWrite(SEG_A, HIGH);
      digitalWrite(SEG_B, HIGH);
      digitalWrite(SEG_C, HIGH);
      digitalWrite(SEG_D, HIGH);
      digitalWrite(SEG_E, LOW);
      digitalWrite(SEG_F, LOW);
      digitalWrite(SEG_G, HIGH);
      break;
    case 4:
      digitalWrite(SEG_A, LOW);
      digitalWrite(SEG_B, HIGH);
      digitalWrite(SEG_C, HIGH);
      digitalWrite(SEG_D, LOW);
      digitalWrite(SEG_E, LOW);
      digitalWrite(SEG_F, HIGH);
      digitalWrite(SEG_G, HIGH);
      break;
    case 5:
      digitalWrite(SEG_A, HIGH);
      digitalWrite(SEG_B, LOW);
      digitalWrite(SEG_C, HIGH);
      digitalWrite(SEG_D, HIGH);
      digitalWrite(SEG_E, LOW);
      digitalWrite(SEG_F, HIGH);
      digitalWrite(SEG_G, HIGH);
      break;
    case 6:
      digitalWrite(SEG_A, HIGH);
      digitalWrite(SEG_B, LOW);
      digitalWrite(SEG_C, HIGH);
      digitalWrite(SEG_D, HIGH);
      digitalWrite(SEG_E, HIGH);
      digitalWrite(SEG_F, HIGH);
      digitalWrite(SEG_G, HIGH);
      break;
    case 7:
      digitalWrite(SEG_A, HIGH);
      digitalWrite(SEG_B, HIGH);
      digitalWrite(SEG_C, HIGH);
      digitalWrite(SEG_D, LOW);
      digitalWrite(SEG_E, LOW);
      digitalWrite(SEG_F, LOW);
      digitalWrite(SEG_G, LOW); 
      break;
    case 8:
      digitalWrite(SEG_A, HIGH);
      digitalWrite(SEG_B, HIGH); 
      digitalWrite(SEG_C,HIGH); 
      digitalWrite(SEG_D,HIGH); 
      digitalWrite(SEG_E,HIGH); 
      digitalWrite(SEG_F,HIGH); 
      digitalWrite(SEG_G,HIGH); 
      break;
    case 9:
      digitalWrite(SEG_A,LOW); 
      digitalWrite(SEG_B,LOW); 
      digitalWrite(SEG_C,LOW); 
      digitalWrite(SEG_D,LOW); 
      digitalWrite(SEG_E,LOW); 
      digitalWrite(SEG_F,LOW); 
      digitalWrite(SEG_G,LOW);   
      break;
    default:
      // Turn off all segments if digit is not valid
      digitalWrite(SEG_A, LOW); 
      digitalWrite(SEG_B, LOW); 
      digitalWrite(SEG_C, LOW); 
      digitalWrite(SEG_D, LOW); 
      digitalWrite(SEG_E, LOW); 
      digitalWrite(SEG_F, LOW); 
      digitalWrite(SEG_G, LOW);   
    }
}