/*
 * 1 inch radius wheel, C = 2pir = 6.283 inches / rev
 * 5 degree encoder wheel, (360 degrees/rev) / (5 degrees/pin change) = 72 pin change/rev) 
 * conversion factor, (6.283 inches/rev) / (72 pin change/rev) = 0.08727 inches / pin change
 * speedometer 
 */

const int window_size = 72;  // (360 degrees/rev)/ (5 degrees / pin change) = 72 pin change / rev)

void speedometer(uint8_t pin) {
  static uint8_t state = 0;
  static uint16_t pulse_count;
  static uint32_t stopwatch_pressed;
  const float pinchange_to_inches = 0.08727;
   
  uint8_t wheel = digitalRead(pin);
    switch (state)
    {
    case 0: // start test
      pulse_count = 0;
      stopwatch_pressed = millis();   // start the stop watch
      state = 1;
      break;
    case 1: // statistics package
      if (pin_change(wheel))
        pulse_count++;   // increment the pulse counter
        if(pulse_count >= window_size){
          float time_period = (millis() - stopwatch_pressed)/1000.0;   // in seconds
          float s = (pinchange_to_inches * (float) pulse_count)/time_period;
          /*
          Serial.print(pulse_count); 
          Serial.print(" ");
          Serial.print(time_period); 
          Serial.print(" ");
          */
          Serial.println(s);
          state = 0;
        }  
      break;
    } // switch-case
} // speedometer

/* simulate with polling a pin change interrupt */
bool pin_change(uint8_t value){       // value may be HIGH or LOw
  static uint8_t last_value = value; // initalize to current value
  bool trigger = false; 
  if (value != last_value){
    last_value = value;              // update to current value
    trigger = true; 
  }
  return trigger;
}

/* running average */

uint16_t runningAverage(uint16_t val)
{
  static uint16_t window[window_size] = {0};   // window into the data stream
  static int index = 0;          // index pointer into the circular buffer
  static uint16_t sum = 0;       // sum of the readings in the buffer

  uint16_t A_0 = window[index];  // oldest value
  uint16_t A_1 = val;            // newest value
  sum += A_1 - A_0;              // subtract out the oldest reading and
                                 // replace with the newest reading.
  // update
  window[index] = A_1;           // update the buffer
  index++;                       // move pointer
  if(index >= window_size){
   index = 0;
  }
  return sum/window_size;        // integer division (round down)  
}

int waitForKey() {
  while (!Serial.available());             // (!Serial) also works
  Serial.print("Hit any key to continue.");
  while (!Serial.available());             // wait for the key
  while(Serial.available()) Serial.read(); // clear the input buffer
  Serial.println(" Running code.");
}