#define DELAY 10000

volatile char *outf, *ink, *outa, *outc, *outl, *outb;
unsigned int digit[10] = {0x3f, 0x06, 0x5b, 0x4f, 0x66, 0x6d, 0x7d, 0x07, 0x7f, 0x6f}; // Patterns for 0-9

int digits[4] = {-1, -1, -1, -1};  // Array to store up to 4 digits, initialized to -1 (no digit)
int currentDigitIndex = 0;  // Index to keep track of which display to update next

void setup() {
    volatile char *dirf, *dirk, *dira, *dirc, *dirl, *dirb;
    dirf = (char *)0x030; // Example address
    dirk = (char *)0x107; // Example address
    dira = (char *)0x021; // Example address
    dirc = (char *)0x027; // Example address
    dirl = (char *)0x10A; // Example address
    dirb = (char *)0x024; // Example address

    // Set port directions
    *dirf = 0x0F;  // Set as output for keypad rows
    *dirk = 0x00;  // Set as input for keypad columns
    *dira = 0xFF;  // Set as output for 7-segment display 1
    *dirc = 0xFF;  // Set as output for 7-segment display 2
    *dirl = 0xFF;  // Set as output for 7-segment display 3
    *dirb = 0xFF;  // Set as output for 7-segment display 4

    // Define port data registers
    outf = (char *)0x031; // Example address
    ink  = (char *)0x106; // Example address
    outa = (char *)0x022; // Example address
    outc = (char *)0x028; // Example address
    outl = (char *)0x10B; // Example address
    outb = (char *)0x025; // Example address
}

void loop() {
    int number = scan_keypad();
    
    if (number != -1 && currentDigitIndex < 4) {  // Check if a valid key is pressed and we have space for more digits
        digits[currentDigitIndex] = number;  // Store the pressed digit
        currentDigitIndex++;  // Move to the next segment
    }

    displayDigits();  // Display the stored digits
    delay1();
}

void displayDigits() {
    // Display the stored digits on the corresponding seven-segment displays
    *outa = 0x00;
    *outc = 0x00;
    *outl = 0x00;
    *outb = 0x00;
    if (digits[0] != -1) *outb = digit[digits[0]];  // Display on the first 7-segment display
    delay1();
    delay1();
    if (digits[1] != -1) *outl = digit[digits[1]];  // Display on the second 7-segment display
    delay1();
    delay1();
    if (digits[2] != -1) *outc = digit[digits[2]];  // Display on the third 7-segment display
    delay1();
    delay1();
    if (digits[3] != -1) *outa = digit[digits[3]];  // Display on the fourth 7-segment display
    delay1();
    delay1();
}

void delay1(void) {
    volatile long j;
    for (j = 0; j < DELAY; j++);
}

int scan_keypad() {
    int i;
    for (i = 0; i < 4; i++) {
        *outf = 1 << i;  // Activate one row at a time
        delay1();
        if (*ink != 0) {
            int key = decode_key(*ink, i);  // Decode the key pressed
            return key;
        }
    }
    return -1;  // No key pressed
}

int decode_key(char input, int row) {
    if (row == 0) {
        if (input == 0x01) return 1;
        else if (input == 0x02) return 2;
        else if (input == 0x04) return 3;
    } else if (row == 1) {
        if (input == 0x01) return 4;
        else if (input == 0x02) return 5;
        else if (input == 0x04) return 6;
    } else if (row == 2) {
        if (input == 0x01) return 7;
        else if (input == 0x02) return 8;
        else if (input == 0x04) return 9;
    } else if (row == 3) {
        if (input == 0x02) return 0;
    }
    return -1;  // Invalid key
}