#include <Adafruit_NeoPixel.h>

#define PIN 0                   // WS2812 data pin on ATtiny85
#define MATRIX_WIDTH  8
#define MATRIX_HEIGHT 4
#define NUMPIXELS     (MATRIX_WIDTH * MATRIX_HEIGHT)

// Zigzag (serpentine) layout object
Adafruit_NeoPixel strip = Adafruit_NeoPixel(NUMPIXELS, PIN, NEO_GRB + NEO_KHZ800);

// Wave animation parameters
float wavePos = 0.0;      // Tracks the wave's diagonal position
float waveSpeed = 0.05;   // Wave movement speed (lower = slower, smoother)

// We’ll define the diagonal “start” and “end” for wavePos
// Bottom-right corner => x=7, y=3 => x+y=10
// Top-left corner     => x=0, y=0 => x+y=0
// We'll let wavePos go from +10 (fully at bottom-right) down to -4 (fully off top-left), then repeat
float waveStart = 10.0;   // wavePos when the wave center is at bottom-right
float waveEnd   = -4.0;   // wavePos when the wave has fully left the top-left

// Convert (x, y) to NeoPixel index in a zigzag layout
int getPixelIndex(int x, int y) {
  // Even rows: left to right
  // Odd rows:  right to left
  if (y % 2 == 0) {
    return y * MATRIX_WIDTH + x;
  } else {
    return y * MATRIX_WIDTH + (MATRIX_WIDTH - 1 - x);
  }
}

void setup() {
  strip.begin();
  strip.show();

  // Start the wave fully at bottom-right corner
  wavePos = waveStart;
}

// Helper: map distance -> brightness with a narrow wave shape
uint8_t waveBrightness(float distance) {
  // Increase multiplier to make the wave narrower
  // e.g. 180 means at distance=1, brightness drops ~180 => 75 left
  uint16_t fadeFactor = 180;

  // Distance-based brightness
  // distance=0 => brightness=255
  // distance=1 => brightness ~ 75
  // distance=1.4 => near 0
  int b = 255 - (int)(abs(distance) * fadeFactor);
  if (b < 0)   b = 0;
  if (b > 255) b = 255;
  return (uint8_t)b;
}

void loop() {
  // Clear first so we only see the wave
  strip.clear();

  // Update every pixel
  for (int y = 0; y < MATRIX_HEIGHT; y++) {
    for (int x = 0; x < MATRIX_WIDTH; x++) {
      // distance from the wave center
      float distance = (x + y) - wavePos;

      // Convert distance -> brightness
      uint8_t b = waveBrightness(distance);
      if (b > 0) {
        // Create a hue in the strict blue range [160..240]
        // Just a small variation so each diagonal pixel isn't the exact same color
        // Adjust as you like or remove variation entirely
        uint8_t baseHue = 160;       // Start of blue range
        uint8_t hueRange = 80;       // 160..239
        uint8_t hue = baseHue + ((uint8_t)((x + y) * 5) % hueRange);

        // Convert hue to a 16-bit value for ColorHSV
        uint16_t hue16 = (uint16_t)hue * 256;

        // Get the final color (HSV -> RGB) with full saturation
        uint32_t color = strip.ColorHSV(hue16, 255, b);
        strip.setPixelColor(getPixelIndex(x, y), color);
      }
    }
  }

  strip.show();

  // Move the wave from bottom-right to top-left
  wavePos -= waveSpeed;

  // Once the wave has fully left the top-left corner, reset
  if (wavePos < waveEnd) {
    wavePos = waveStart;
  }

  // Lower delay => smoother but uses more CPU
  delay(25);
}