// based on https://gist.github.com/kriegsman/5adca44e14ad025e6d3b

#include "FastLED.h"

// Matrix size
#define NUM_ROWS 16
#define NUM_COLS 16

#define DATA_PIN 2
#define BRIGHTNESS 200
#define NUM_LEDS NUM_ROWS * NUM_COLS
#define LED_TYPE    WS2812B
#define COLOR_ORDER GRB
// Define the array of leds
CRGB leds[NUM_LEDS];
byte rain[NUM_LEDS];
//byte counter = 1;
int speed = 1;

const uint8_t kMatrixWidth = 16;
const uint8_t kMatrixHeight = 16;
const bool    kMatrixSerpentineLayout = false;

void setup() {
  //delay(1000); 

  FastLED.addLeds<LED_TYPE,DATA_PIN,COLOR_ORDER>(leds, NUM_LEDS); //setCorrection(TypicalLEDStrip);
  //FastLED.addLeds<LED_TYPE,DATA_PIN,CLK_PIN,COLOR_ORDER>(leds, NUM_LEDS).setCorrection(TypicalLEDStrip);
  // set master brightness control
  FastLED.setBrightness(BRIGHTNESS);
  raininit();
  //Serial.begin(115200);
 // Serial.println("Hello, I'm in a terminal!");

}

void loop() {
  EVERY_N_MILLISECONDS(80) {
    updaterain();
    FastLED.show();
  }
  EVERY_N_MILLISECONDS(30) {
    changepattern();
  }
} //loop

void changepattern () {
  int rand1 = random16 (NUM_LEDS);
  int rand2 = random16 (NUM_LEDS);
  if ((rain[rand1] == 1) && (rain[rand2] == 0) )   //simple get two random dot 1 and 0 and swap it,
  {
    rain[rand1] = 0;  //this will not change total number of dots
    rain[rand2] = 1;
  }
} //changepattern

void raininit() {                               //init array of dots. run once
  for (int i = 0; i < NUM_LEDS; i++) {
    if (random8(10) == 0) {
      rain[i] = 1;  //random8(20) number of dots. decrease for more dots
    }
    else {
      rain[i] = 0;
    }
  }
} //raininit

void updaterain() {
  for (byte i = 0; i < NUM_COLS; i++) {
    for (byte j = 0; j < NUM_ROWS; j++) {
      byte layer = rain[XY(i, ((j + speed + NUM_ROWS) % NUM_ROWS))];   //fake scroll based on shift coordinate
      // random8(2) add glitchy look
      if (layer) {
        leds[XY(i,j)] = CHSV(110, 255, 255);

       // Serial.print(NUM_COLS-1-i);Serial.print("  ");
      //  Serial.print(NUM_ROWS-1-j);Serial.print("  ");
      //  Serial.print(speed);Serial.println(" ");
      }
    }
  }
 // Serial.println("Update terrain");
  speed ++;
  fadeToBlackBy(leds, NUM_LEDS, 80);
  //blurRows(leds, NUM_COLS, NUM_ROWS, 16);      //if you want
} //updaterain

uint16_t XY( uint8_t x, uint8_t y)
{
  uint16_t i;
  
  if( kMatrixSerpentineLayout == false) {
    i = (y * kMatrixWidth) + x;
  }

  if( kMatrixSerpentineLayout == true) {
    if( y & 0x01) {
      // Odd rows run backwards
      uint8_t reverseX = (kMatrixWidth - 1) - x;
      i = (y * kMatrixWidth) + reverseX;
    } else {
      // Even rows run forwards
      i = (y * kMatrixWidth) + x;
    }
  }
  return i;
}