#include <Wire.h>
#include <LedControl.h>

LedControl lc = LedControl(11, 13, 10, 1);  // DIN, CLK, CS
#define N 8

float height[N][N];     
float velX[N][N];       
float velY[N][N];       
int16_t ax, ay;

void setup() {
  Wire.begin();
  lc.shutdown(0, false);
  lc.setIntensity(0, 7);
  lc.clearDisplay(0);

  Wire.beginTransmission(0x68);
  Wire.write(0x6B);
  Wire.write(0);
  Wire.endTransmission(true);

  //  calm pool
  for (int x = 0; x < N; x++)
    for (int y = 0; y < N; y++) {
      height[x][y] = 3.5;
      velX[x][y] = 0;
      velY[x][y] = 0;
    }
}

void loop() {
  Wire.beginTransmission(0x68);
  Wire.write(0x3B);
  Wire.endTransmission(false);
  Wire.requestFrom(0x68, 4, true);
  ax = (Wire.read() << 8) | Wire.read();
  ay = (Wire.read() << 8) | Wire.read();

  // Normalize acceleration
  float gx = -ax / 16384.0 * 0.4;
  float gy = -ay / 16384.0 * 0.4;

  for (int x = 0; x < N; x++) {
    for (int y = 0; y < N; y++) {
      velX[x][y] += gx;
      velY[x][y] += gy;
      
      // Damping
      velX[x][y] *= 0.95;
      velY[x][y] *= 0.95;
    }
  }

  float newHeight[N][N];
  for (int x = 0; x < N; x++)
    for (int y = 0; y < N; y++)
      newHeight[x][y] = 0;

  for (int x = 0; x < N; x++) {
    for (int y = 0; y < N; y++) {
      int nx = x + (int)(velX[x][y] + 0.5);
      int ny = y + (int)(velY[x][y] + 0.5);
      
      // Keep in bounds
      nx = constrain(nx, 0, N-1);
      ny = constrain(ny, 0, N-1);
      
      float flowAmount = height[x][y] * 0.7;
      newHeight[nx][ny] += flowAmount;
      newHeight[x][y] += height[x][y] * 0.3;
    }
  }

  for (int x = 0; x < N; x++) {
    for (int y = 0; y < N; y++) {
      float sum = newHeight[x][y];
      int count = 1;
      
      if (x > 0) { sum += newHeight[x-1][y]; count++; }
      if (x < N-1) { sum += newHeight[x+1][y]; count++; }
      if (y > 0) { sum += newHeight[x][y-1]; count++; }
      if (y < N-1) { sum += newHeight[x][y+1]; count++; }
      
      height[x][y] = sum / count;
      height[x][y] = constrain(height[x][y], 0.5, 7.5);
    }
  }

  lc.clearDisplay(0);
  for (int col = 0; col < N; col++) {
    for (int row = 0; row < N; row++) {
      int h = (int)height[col][row];
      if ((7 - row) < h) {
        lc.setLed(0, row, col, true);
      }
    }
  }

  delay(40);
}