#include <Arduino.h>
#include <math.h>

#define CLK 13
#define DIN 11
#define CS  10
#define X_SEGMENTS   4
#define Y_SEGMENTS   4
#define NUM_SEGMENTS (X_SEGMENTS * Y_SEGMENTS)

byte fb[8 * NUM_SEGMENTS];

// 8x8 font for digits 0-9
const byte digit[10][8] = {
  {0x3C,0x66,0x6E,0x76,0x66,0x66,0x3C,0x00}, // 0
  {0x18,0x38,0x18,0x18,0x18,0x18,0x3C,0x00}, // 1
  {0x3C,0x66,0x06,0x0C,0x18,0x30,0x7E,0x00}, // 2
  {0x3C,0x66,0x06,0x1C,0x06,0x66,0x3C,0x00}, // 3
  {0x0C,0x1C,0x3C,0x6C,0x7E,0x0C,0x1E,0x00}, // 4
  {0x7E,0x60,0x7C,0x06,0x06,0x66,0x3C,0x00}, // 5
  {0x1C,0x30,0x60,0x7C,0x66,0x66,0x3C,0x00}, // 6
  {0x7E,0x66,0x06,0x0C,0x18,0x18,0x18,0x00}, // 7
  {0x3C,0x66,0x66,0x3C,0x66,0x66,0x3C,0x00}, // 8
  {0x3C,0x66,0x66,0x3E,0x06,0x0C,0x38,0x00}  // 9
};

void shiftAll(byte send_to_address, byte send_this_data) {
  digitalWrite(CS, LOW);
  for (int i = 0; i < NUM_SEGMENTS; i++) {
    shiftOut(DIN, CLK, MSBFIRST, send_to_address);
    shiftOut(DIN, CLK, MSBFIRST, send_this_data);
  }
  digitalWrite(CS, HIGH);
}

void set_pixel(uint8_t x, uint8_t y, uint8_t mode) {
  byte *addr = &fb[x / 8 + y * X_SEGMENTS];
  byte mask = 128 >> (x % 8);
  switch (mode) {
    case 0: *addr &= ~mask; break;
    case 1: *addr |= mask;  break;
    case 2: *addr ^= mask;  break;
  }
}

void safe_pixel(uint8_t x, uint8_t y, uint8_t mode) {
  if ((x >= X_SEGMENTS * 8) || (y >= Y_SEGMENTS * 8)) return;
  set_pixel(x, y, mode);
}

void clear() {
  byte *addr = fb;
  for (byte i = 0; i < 8 * NUM_SEGMENTS; i++) *addr++ = 0;
}

void show() {
  for (byte row = 0; row < 8; row++) {
    digitalWrite(CS, LOW);
    byte segment = NUM_SEGMENTS;
    while (segment--) {
      byte x = segment % X_SEGMENTS;
      byte y = segment / X_SEGMENTS * 8;
      byte addr = (row + y) * X_SEGMENTS;

      if (segment & X_SEGMENTS) { // odd rows
        shiftOut(DIN, CLK, MSBFIRST, 8 - row);
        shiftOut(DIN, CLK, LSBFIRST, fb[addr + x]);
      } else { // even rows
        shiftOut(DIN, CLK, MSBFIRST, 1 + row);
        shiftOut(DIN, CLK, MSBFIRST, fb[addr - x + X_SEGMENTS - 1]);
      }
    }
    digitalWrite(CS, HIGH);
  }
}

void draw_digit(byte num, int x_offset, int y_offset) {
  if (num > 9) return;
  for (byte row = 0; row < 8; row++) {
    byte rowdata = digit[num][row];
    for (byte col = 0; col < 8; col++) {
      byte pixel = (rowdata >> (7 - col)) & 0x01;
      safe_pixel(x_offset + col, y_offset + row, pixel);
    }
  }
}

void setup() {
  Serial.begin(115200);
  pinMode(CLK, OUTPUT);
  pinMode(DIN, OUTPUT);
  pinMode(CS, OUTPUT);

  shiftAll(0x0f, 0x00); // display test off
  shiftAll(0x0b, 0x07); // scan limit 0-7
  shiftAll(0x0c, 0x01); // normal operation
  shiftAll(0x0a, 0x0f); // max brightness
  shiftAll(0x09, 0x00); // no decode
  clear();
  show();
}

void loop() {
  String input = "1234"; // default number to show
  // If Wokwi Serial Monitor is used, override default
  while (Serial.available()) {
    char c = Serial.read();
    if (c >= '0' && c <= '9') input += c;
  }

  clear();
  int x = 0;
  for (int i = 0; i < input.length(); i++) {
    if (isDigit(input[i])) {
      draw_digit(input[i] - '0', x, 0);
      x += 8;
    }
  }
  show();
  delay(1000);
}