const int MAX_LEVEL = 100;
int sequence[MAX_LEVEL];
int your_sequence[MAX_LEVEL];
int level = 1;
int velocity = 1000;

void setup() {
  pinMode(34, INPUT);
  pinMode(35, INPUT);
  pinMode(32, INPUT);
  pinMode(25, INPUT);

  pinMode(23, OUTPUT);
  pinMode(22, OUTPUT);
  pinMode(21, OUTPUT);
  pinMode(19, OUTPUT);

  digitalWrite(23, LOW);
  digitalWrite(22, LOW);
  digitalWrite(21, LOW);
  digitalWrite(19, LOW);
}

void loop() {
  if (level == 1) {
    generate_sequence(); //generiert eine Sequenz
  }

  if (digitalRead(25) == LOW || level != 1) {
    show_sequence();
    get_sequence();
  }
}

void show_sequence() {
  for (int i = 0; i < level; i++) {
    digitalWrite(sequence[i], HIGH);
    delay(velocity);
    digitalWrite(sequence[i], LOW);
    delay(200);
  }
}

void get_sequence() {
  int flag = 0; //this flag indicates if the sequence is correct

  for (int i = 0; i < level; i++) {
    flag = 0;
    while (flag == 0) {
      if (digitalRead(34) == LOW) {
        your_sequence[i] = 19;
        digitalWrite(19, HIGH);
        delay(200);
        digitalWrite(19, LOW);
        flag = 1;
      } else if (digitalRead(35) == LOW) {
        your_sequence[i] = 21;
        digitalWrite(21, HIGH);
        delay(200);
        digitalWrite(21, LOW);
        flag = 1;
      } else if (digitalRead(32) == LOW) {
        your_sequence[i] = 22;
        digitalWrite(22, HIGH);
        delay(200);
        digitalWrite(22, LOW);
        flag = 1;
      } else if (digitalRead(25) == LOW) {
        your_sequence[i] = 23;
        digitalWrite(23, HIGH);
        delay(200);
        digitalWrite(23, LOW);
        flag = 1;
      }
    }

    if (your_sequence[i] != sequence[i]) {
      wrong_sequence();
      return;
    }
  }
  right_sequence();
}

void generate_sequence() {
  randomSeed(millis()); //in this way is really random!!!

  for (int i = 0; i < MAX_LEVEL; i++) {
    sequence[i] = random(19, 24); // random between 19 (inclusive) and 24 (exclusive)
  }
}

void wrong_sequence() {
  for (int i = 0; i < 3; i++) {
    digitalWrite(23, HIGH);
    digitalWrite(22, HIGH);
    digitalWrite(21, HIGH);
    digitalWrite(19, HIGH);
    delay(250);
    digitalWrite(23, LOW);
    digitalWrite(22, LOW);
    digitalWrite(21, LOW);
    digitalWrite(19, LOW);
  }
  level = 1;
  velocity = 1000;
}

void right_sequence() {
  digitalWrite(23, LOW);
  digitalWrite(22, LOW);
  digitalWrite(21, LOW);
  digitalWrite(19, LOW);
  delay(250);

  digitalWrite(23, HIGH);
  digitalWrite(22, HIGH);
  digitalWrite(21, HIGH);
  digitalWrite(19, HIGH);
  delay(500);
  digitalWrite(23, LOW);
  digitalWrite(22, LOW);
  digitalWrite(21, LOW);
  digitalWrite(19, LOW);

  if (level < MAX_LEVEL)
    level++;

  velocity -= 50; //increase difficulty
}