#define clockPin 10 // Clock pin of 74HC595 is connected to Digital pin 10
#define dataPin  9  // Data  pin of 74HC595 is connected to Digital pin 9 
#define latchPin 8  // Latch pin of 74HC595 is connected to Digital pin 8

int numOfRegisters = 2;
byte* registerState;

long effectId = 0;
long prevEffect = 0;
long effectRepeat = 0;
long effectSpeed = 30;

void setup() { // setup() - this function runs once when you turn your Arduino on
  //Initialize array
  registerState = new byte[numOfRegisters];
  for (size_t i = 0; i < numOfRegisters; i++) {
    registerState[i] = 0;
  }

  //set pins to output so you can control the shift register
  pinMode(latchPin, OUTPUT);
  pinMode(clockPin, OUTPUT);
  pinMode(dataPin, OUTPUT);
}

void loop() { //loop() - this function runs over and over again
  do {
    effectId = random(6);
  } while (effectId == prevEffect);
  prevEffect = effectId;

  switch (effectId)
  {
    case 0:
      effectRepeat = random(1, 2);
      break;
    case 1:
      effectRepeat = random(1, 2);
      break;
    case 3:
      effectRepeat = random(1, 5);
      break;
    case 4:
      effectRepeat = random(1, 2);
      break;
    case 5:
      effectRepeat = random(1, 2);
      break;
  }

  for (int i = 0; i < effectRepeat; i++) {
    effectSpeed = random(10, 90);
    switch (effectId) {
      case 0:
        effectA(effectSpeed);
        break;
      case 1:
        effectB(effectSpeed);
        break;
      case 3:
        effectC(effectSpeed);
        break;
      case 4:
        effectD(effectSpeed);
        break;
      case 6:
        effectE(effectSpeed);
        break;
    }
  }
}

void effectA(int speed) {
  for (int i = 0; i < 16; i++) {
    for (int k = i; k < 16; k++) {
      regWrite(k, HIGH);
      delay(speed);
      regWrite(k, LOW);
    }
    regWrite(i, HIGH);
  }
}

void effectB(int speed) {
  for (int i = 15; i >= 0; i--) {
    for (int k = 0; k < i; k++) {
      regWrite(k, HIGH);
      delay(speed);
      regWrite(k, LOW);
    }
    regWrite(i, HIGH);
  }
}

void effectC(int speed) {
  int prevI = 0;
  for (int i = 0; i < 16; i++) {
    regWrite(prevI, LOW);
    regWrite(i, HIGH);
    prevI = i;
    delay(speed);
  }

  for (int i = 15; i >= 0; i--) {
    regWrite(prevI, LOW);
    regWrite(i, HIGH);
    prevI = i;
    delay(speed);
  }
}

void effectD(int speed) {
  for (int i = 0; i < 8; i++) {
    for (int k = i; k < 8; k++) {
      regWrite(k, HIGH);
      regWrite(15 - k, HIGH);
      delay(speed);
      regWrite(k, LOW);
      regWrite(15 - k, LOW);
    }
    regWrite(i, HIGH);
    regWrite(15 - i, HIGH);
  }
}

void effectE(int speed) {
  for (int i = 7; i >= 0; i--) {
    for (int k = 0; k <= i; k++) {
      regWrite(k, HIGH);
      regWrite(15 - k, HIGH);
      delay(speed);
      regWrite(k, LOW);
      regWrite(15 - k, LOW);
    }
    regWrite(i, HIGH);
    regWrite(15 - i, HIGH);
  }
}

void regWrite(int pin, bool state) {
  int reg = pin / 8; //Determines register
  int actualPin = pin - (8 * reg);  //Determines pin for actual register
  digitalWrite(latchPin, LOW);  //Begin session
  for (int i = 0; i < numOfRegisters; i++) { //Get actual states for register
    byte* states = &registerState[i];
    //Update state
    if (i == reg) {
      bitWrite(*states, actualPin, state);
    }
    //Write
    shiftOut(dataPin, clockPin, MSBFIRST, *states);
  }
  digitalWrite(latchPin, HIGH); //End session
}