// Press the green button to fade-in,
// and the Blue button to fade out.

#include <FastLED.h>

// Pins:
#define DATA_PIN 8
#define BTN_FADE_IN 3
#define BTN_FADE_OUT 2

// How many leds in your strip?
#define NUM_LEDS 3

// Delay between each fade step
#define FADE_DELAY 10

CRGB leds[NUM_LEDS];

void setup() {
  FastLED.addLeds<NEOPIXEL, DATA_PIN>(leds, NUM_LEDS);  // GRB ordering is assumed
  pinMode(BTN_FADE_IN, INPUT_PULLUP);
  pinMode(BTN_FADE_OUT, INPUT_PULLUP);
}

void fadeIn() {
  for (int v = 0; v <= 255; v++) {
    fill_solid(leds, NUM_LEDS, CHSV(255, 255, v));
    FastLED.show();
    delay(FADE_DELAY);
  }
}

void fadeOut() {
  for (int v = 255; v >= 0; --v) {
    fill_solid(leds, NUM_LEDS, CHSV(255, 255, v));
    FastLED.show();
    delay(FADE_DELAY);
  }
}

void loop() {
  if (!digitalRead(BTN_FADE_IN)) {
    fadeIn();
  }

  // Fade out
  if (!digitalRead(BTN_FADE_OUT)) {
    fadeOut();
  }
}