const int LED_RED = 4;
const int LED_GREEN = 3;
const int LED_BLUE = 2;
const int BUTTON_RED_UP = 5;
const int BUTTON_RED_DOWN = 6;
const int BUTTON_GREEN_UP = 7;
const int BUTTON_GREEN_DOWN = 8;
const int BUTTON_BLUE_UP = 9;
const int BUTTON_BLUE_DOWN = 10;

int curButtonRedUp = LOW;
int lastButtonRedUp = LOW;
int curButtonRedDown = LOW;
int lastButtonRedDown = LOW;

int curButtonGreenUp = LOW;
int lastButtonGreenUp = LOW;
int curButtonGreenDown = LOW;
int lastButtonGreenDown = LOW;

int curButtonBlueUp = LOW;
int lastButtonBlueUp = LOW;
int curButtonBlueDown = LOW;
int lastButtonBlueDown = LOW;

int buttonRedBrightState = 0;
int buttonGreenBrightState = 0;
int buttonBlueBrightState = 0;

int debounce(const int last, const int button)
{
  int current = digitalRead(button);
  if (current != last)
  {
    delay(5);
    current = digitalRead(button);
  }
  return current;
}

void changeLedBrightStateUp(int& lastButton, int& curButton, int& buttonBrightState, int BUTTON, int LED)
{
  curButton = debounce(lastButton, BUTTON);

  if (curButton == HIGH && lastButton == LOW)
  {
    buttonBrightState += 50;
    if (buttonBrightState > 250)
    {
      buttonBrightState = 250;
    }
    analogWrite(LED, buttonBrightState);
  }
  lastButton = curButton;
}

void changeLedBrightStateDown(int& lastButton, int& curButton, int& buttonBrightState, int BUTTON, int LED)
{
  curButton = debounce(lastButton, BUTTON);

  if (curButton == HIGH && lastButton == LOW)
  {
    buttonBrightState -= 50;
    if (buttonBrightState < 0)
    {
      buttonBrightState = 0;
    }
    analogWrite(LED, buttonBrightState);
  }
  lastButton = curButton;
}

void setup() {
  // put your setup code here, to run once:
  pinMode(LED_RED, OUTPUT);
  pinMode(LED_GREEN, OUTPUT);
  pinMode(LED_BLUE, OUTPUT);
  digitalWrite(LED_RED, LOW);
  digitalWrite(LED_GREEN, LOW);
  digitalWrite(LED_BLUE, LOW);

  pinMode(BUTTON_RED_UP, INPUT);
  pinMode(BUTTON_RED_DOWN, INPUT);
  digitalWrite(BUTTON_RED_UP, LOW);
  digitalWrite(BUTTON_RED_DOWN, LOW);

  pinMode(BUTTON_GREEN_UP, INPUT);
  pinMode(BUTTON_GREEN_DOWN, INPUT);
  digitalWrite(BUTTON_GREEN_UP, LOW);
  digitalWrite(BUTTON_GREEN_DOWN, LOW);

  pinMode(BUTTON_BLUE_UP, INPUT);
  pinMode(BUTTON_BLUE_DOWN, INPUT);
  digitalWrite(BUTTON_BLUE_UP, LOW);
  digitalWrite(BUTTON_BLUE_DOWN, LOW);

}

void loop() {
  // put your main code here, to run repeatedly:
  changeLedBrightStateUp(lastButtonRedUp, curButtonRedUp, buttonRedBrightState, BUTTON_RED_UP, LED_RED);
  changeLedBrightStateDown(lastButtonRedDown, curButtonRedDown, buttonRedBrightState, BUTTON_RED_DOWN, LED_RED);

  changeLedBrightStateUp(lastButtonGreenUp, curButtonGreenUp, buttonGreenBrightState, BUTTON_GREEN_UP, LED_GREEN);
  changeLedBrightStateDown(lastButtonGreenDown, curButtonGreenDown, buttonGreenBrightState, BUTTON_GREEN_DOWN, LED_GREEN);

  changeLedBrightStateUp(lastButtonBlueUp, curButtonBlueUp, buttonBlueBrightState, BUTTON_BLUE_UP, LED_BLUE);
  changeLedBrightStateDown(lastButtonBlueDown, curButtonBlueDown, buttonBlueBrightState, BUTTON_BLUE_DOWN, LED_BLUE);
}