#include <FastLED.h>
#include <math.h> //Needed for some math functions.

#define LED_PIN     2
#define NUM_LEDS    60
#define BRIGHTNESS  180
#define LED_TYPE    WS2812B
#define COLOR_ORDER GRB

CRGB leds[NUM_LEDS];

//Constants - tweak these to change appearance
const double MAX_SPEED = 375.0;
const double NEW_PARTICLE_PROBABILITY = 0.01;
const double PARTICLE_PREIGNITION_TIME = 0.0;
const double PARTICLE_IGNITION = 0.2;
const double PARTICLE_HOLD_TIME = 0.0;
const double PARTICLE_FADE_TIME = 2.0;

// Structure to represent a particle
struct Particle {
  CRGB color;
  unsigned long birthTime; // milliseconds since start
  double velocity;
  double position;
};

// Particle array (using a fixed-size array for simplicity on Arduino)
#define MAX_PARTICLES 50 // Limit the number of concurrent particles
Particle particles[MAX_PARTICLES];
int numParticles = 0; // Keep track of how many particles are active

// Function to add a new particle to the system
void addParticle(CRGB color, double pos, double maxSpeed) {
    if (numParticles < MAX_PARTICLES) {  //Check we haven't exceeded our limit.
        Particle& p = particles[numParticles];
        p.position = pos;
        p.velocity = ((double)random(0, 1000) / 1000.0) * maxSpeed * 2 - maxSpeed; //Random value between -maxSpeed and maxSpeed;
        p.color = color;
        p.birthTime = millis();
        numParticles++;
    }
}

// Function to update all particles and remove dead ones
void updateParticles() {
  for (int i = 0; i < numParticles; i++) {
    Particle& p = particles[i];

    unsigned long now = millis();
    double age = (now - p.birthTime) / 1000.0; // Age in seconds

    // Calculate time since last update (simple version for now)
    double deltaTime = 0.02; // Approximate frame time (adjust as needed)
    p.position += p.velocity * deltaTime;
    p.velocity -= (2 * p.velocity * deltaTime);

    // Fade the color. Important to do this with a temporary copy, then overwrite.
    CRGB fadedColor = p.color;

    // Random amount to fade
    fadedColor.fadeToBlackBy((float)random(0, 101) / 1000.0f * 100);

    p.color = fadedColor;

    //Particle Size Calc
    double fade = 0.0;
    if (age > PARTICLE_PREIGNITION_TIME && age < PARTICLE_IGNITION + PARTICLE_PREIGNITION_TIME) {
      p.color = CRGB::White;
    }
    else {
      if (age < PARTICLE_PREIGNITION_TIME) {
        fade = 1.0 - (age / PARTICLE_PREIGNITION_TIME);
      }
      else {
        double adjustedAge = age - PARTICLE_PREIGNITION_TIME;

        if (adjustedAge < PARTICLE_HOLD_TIME + PARTICLE_IGNITION) {
          fade = 0.0;
        }
        else if (adjustedAge > PARTICLE_HOLD_TIME + PARTICLE_IGNITION + PARTICLE_FADE_TIME) {
          fade = 1.0;
        }
        else {
          adjustedAge -= (PARTICLE_HOLD_TIME + PARTICLE_IGNITION);
          fade = adjustedAge / PARTICLE_FADE_TIME;
        }
      }
      p.color.fadeToBlackBy((float)(fade * 255)); //Faster Fading
    }

    //Particle Removal
    if (age > PARTICLE_HOLD_TIME + PARTICLE_IGNITION + PARTICLE_FADE_TIME) {
      // Remove the particle by shifting the rest of the array
      for (int j = i; j < numParticles - 1; j++) {
        particles[j] = particles[j+1];
      }
      numParticles--;
      i--; // Re-check current index after shifting
    }
  }
}

// Function to draw the particles on the LED strip
void drawParticles() {
  // Clear the LED strip
  fill_solid(leds, NUM_LEDS, CRGB::Black);

  // Draw each particle
  for (int i = 0; i < numParticles; i++) {
    Particle& p = particles[i];
    int ledIndex = (int)round(p.position); // Get the nearest LED index
    if (ledIndex >= 0 && ledIndex < NUM_LEDS) {
      leds[ledIndex] = p.color; // Set the LED color to the particle's color
    }
  }
}

void setup() {
  delay(3000); // Sanity delay
  FastLED.addLeds<LED_TYPE, LED_PIN, COLOR_ORDER>(leds, NUM_LEDS); // Removed setCorrection()
  FastLED.setBrightness( BRIGHTNESS );
  FastLED.clear();
  FastLED.show();
  randomSeed(analogRead(0));
}

void loop() {

    //Create the particle effect on each run
    if (random(0, 1000) / 1000.0 < NEW_PARTICLE_PROBABILITY) {
      //Create the random colour.
        CRGB color = CHSV(random(255), 255, 255);
      //Get the position.
        uint16_t iStartPos = random(NUM_LEDS);

        int c = random(10,50);

        double multiplier = (double)random(0, 1000) / 1000.0 * 3.0;

        for (int i = 1; i < c; i++) {
          addParticle(color, iStartPos, MAX_SPEED * (double)random(0, 1000) / 1000.0 * multiplier);
        }
    }

    updateParticles();
    drawParticles();

    FastLED.show();
    delay(20);
}