/* A simple program to blink the LED every 500 milliseconds. 
When the push button is pressed the LED blinking frequency should be double. 
(use hardware interrupts).*/

// Pin definitions
#define BUTTON_PIN 3
#define LED_PIN 13

// LED blinking stuff
int blinkDelay;                       // LED blink delay
bool doubledFrequencyState = false;   // whether LED blinking frequency is fast (true = 250ms/doubled) or slow (false = 500ms)

// Debouncing timing
unsigned long debounceDuration = 50; // how long to wait before validating next change in button state (millis)
unsigned long lastInterrupt = 0;     // starting point to compare debounce duration to
unsigned long interruptTime;         // time program was interrupted

void setup() {

  // setup serial
  Serial.begin(115200); 
  
  // Setup LED pin as output
  pinMode(LED_PIN, OUTPUT);

  // Setup button pins with internal pull resistors
  pinMode(BUTTON_PIN, INPUT_PULLUP);
  
  // Interrupts attached for button - triggered when pin goes from low to high.
  attachInterrupt(digitalPinToInterrupt(BUTTON_PIN), toggleLEDSpeed, RISING); 

}

//ISR - external interupt to toggle the doubled frequency state with debouncing
void toggleLEDSpeed(){
  // Set interrupt time to number of ms passed since program started running
  interruptTime = millis();

  // Only start the button functionality if enough time has past (i.e. update time is greater than debounce duration)
  if (interruptTime - lastInterrupt > debounceDuration) {
    
    
    // Update starting point for the debounce timer
    lastInterrupt = interruptTime;
          
    // toggle state
    doubledFrequencyState = !doubledFrequencyState;
  }
}

void loop() {

  // Decide blink frequency depending on button press
  if (doubledFrequencyState) {
    blinkDelay = 250;
     Serial.print("Blink delay is: ");
    Serial.println(blinkDelay);
  } else {
    blinkDelay = 500;
    Serial.print("Blink delay is: ");
    Serial.println(blinkDelay);
  }

  // Blink LED depending on delay
  digitalWrite(LED_PIN, HIGH);
  delay(blinkDelay);
  digitalWrite(LED_PIN, LOW);
  delay(blinkDelay);

}