#include <Adafruit_NeoPixel.h>

#define MATRIX_PIN 2
#define ROWS 16
#define COLS 16
#define NUM_PIXELS (ROWS * COLS)

Adafruit_NeoPixel matrix(NUM_PIXELS, MATRIX_PIN, NEO_GRB + NEO_KHZ800);

int x[256];
int y[256];
int snakelen = 3;
int xa, ya;
int fx, fy;

void setup() {
  pinMode(A0, INPUT);
  pinMode(A1, INPUT);
  matrix.begin();
  fx = random(COLS);
  fy = random(ROWS);
}

void loop() {
  int horz = analogRead(A1);
  int vert = analogRead(A0);

  if (horz == 0 and vert == 512 and xa == 0) {xa = 1; ya = 0;}
  if (horz == 1023 and vert == 512 and xa == 0) {xa = -1; ya = 0;}
  if (horz == 512 and vert == 0 and ya == 0) {ya = 1; xa = 0;}
  if (horz == 512 and vert == 1023 and ya == 0) {ya = -1; xa = 0;}


  int nextx = (x[0] + xa + COLS) % COLS;
  int nexty = (y[0] + ya + ROWS) % ROWS;

  for (int i = snakelen - 1; i > 0; i--) {
    x[i] = x[i - 1];
    y[i] = y[i - 1];
  }
  
  x[0] = nextx;
  y[0] = nexty;

  for (int i = 1; i < snakelen; i++) {
    if (nextx == x[i] and nexty == y[i]) {
      snakelen = 3;
    }
  }


  if(nextx == fx and nexty == fy) {
    snakelen += 1;
    matrix.setPixelColor(fy * COLS + fx, matrix.Color(0, 0, 0));
    fx = random(COLS);
    fy = random(ROWS);
  }


  matrix.clear();

  matrix.setPixelColor(fy * COLS + fx, matrix.Color(255, 0, 0));

  for(int i = 0; i < snakelen; i++) {
    int index = y[i] * COLS + x[i];
    matrix.setPixelColor(index, matrix.Color(0, 255, 0));
  }
  matrix.show();
  delay(125);
}