// Public domain, by Chad Miller
// Photo of layout at
//   http://picasaweb.google.com/chadmill/Arduino#5563199409956300850

// Map pins to color inputs of LED.
int red = 9;
int blue = 10;
int green = 11;

unsigned long last_beat = 0;
unsigned long tick = 0;

void setup() {                
  pinMode(13, OUTPUT); // pseudo-pin leading to on-board LED
  pinMode(red, OUTPUT);
  pinMode(blue, OUTPUT);
  pinMode(green, OUTPUT);
  last_beat = millis();
}

unsigned long lightread() {
  int a = constrain(analogRead(0), 0, 900); // delay(d) hates nonpositive
  int lr = 2000 - map(a, 0, 900, 500, 1990);
  return lr;
}

//>>> r = "==  = ="
//>>> b = " ==  =="
//>>> g = "   ===="
//>>> for i, trio in enumerate(zip(r,g,b)):
//...    trio = map((lambda s: s == "="), trio)
//...    print "    case {}:".format(i)
//...    for pin, new, old in zip((9, 10, 11), trio, states):
//...      if old != new:
//...        if new:
//...          print "      digitalWrite({}, HIGH);".format(pin)
//...        else:
//...          print "      digitalWrite({}, LOW);".format(pin)
//...    print "      break;"
//...    print
//...    states = trio

void go_next(unsigned long tick) {
  switch (tick % 7) {
    case 0:
      digitalWrite(10, LOW);
      break;

    case 1:
      digitalWrite(11, HIGH);
      break;

    case 2:
      digitalWrite(9, LOW);
      break;

    case 3:
      digitalWrite(10, HIGH);
      digitalWrite(11, LOW);
      break;

    case 4:
      digitalWrite(9, HIGH);
      break;

    case 5:
      digitalWrite(9, LOW);
      digitalWrite(11, HIGH);
      break;

    case 6:
      digitalWrite(9, HIGH);
      break;
  }
}

void loop() {
  unsigned long now = millis();
  unsigned long wanted_delay = lightread();
  if (now > (last_beat + wanted_delay)) {
    tick += 1;
    go_next(tick);
    last_beat = now;
  }
}