// https://wokwi.com/projects/373589174724221953
// https://forum.arduino.cc/t/measure-time-that-a-condition-is-true-to-then-trigger-and-action/1159366

unsigned long durationMillis = 500; // DURATION for LED ON after BUTTON is pressed

#define buttonPin 2 // the Arduino pin connected to the BUTTON
#define ledPin 3    // the Arduino pin connected to the LED

bool ledState;    // store the state (ON/OFF) of the LED
bool buttonState; // store the state (pressed/not pressed) of the button

unsigned long ledOnMillis; // timer for LED ON time
unsigned long ledOffMillis; // timer for LED OFF time

void setup() {
  Serial.begin(115200); // start Serial Monitor communications 
  pinMode (ledPin, OUTPUT); // set Arduino pin for the LED to OUTPUT
  pinMode (buttonPin, INPUT_PULLUP); // set Arduino pin for the BUTTON to INPUT with PULLUP resistor
  digitalWrite(ledPin, LOW); // LED OFF
  welcome();
}

void loop() {
  bool buttonReading = !digitalRead(buttonPin);
  unsigned long now = millis();

  bool buttonEvent = false;    // unless...

  if (buttonReading != buttonState) {
    buttonState = buttonReading;

    if (buttonState)
      buttonEvent = true;     // we saw the button go down
  }

  if (buttonEvent) {
    ledOnMillis = millis(); // record LED ON time

    digitalWrite(ledPin, HIGH);  // LED ON
    ledState = 1; // set LED flag meaning LED is ON
    printOn(); // format and print current status
  }

  if ((millis() - ledOnMillis > durationMillis) && ledState) { // difference between button to now
    ledOffMillis = millis(); // get LED OFF time
    digitalWrite(ledPin, LOW); // LED OFF
    ledState = 0; // clear LED flag
    printOff(); // format and print current status
    duration();
  }

  delay(10);  // poor man's debouncing
}

//*************************************************************
// Formatted printout
//*************************************************************

void printOn() {
  Serial.print("TIME ON  ");
  Serial.print(ledOnMillis);
  Serial.print(" <-- the milliseconds clock");
  Serial.println();
}

void printOff () {
  Serial.print("TIME OFF ");
  Serial.print(ledOffMillis);
  Serial.print(" <-- DURATION plus current milliseconds clock");
  Serial.println();
}

void duration () {
  Serial.print("DURATION  ");
  Serial.print(ledOffMillis - ledOnMillis); // show duration
  Serial.print(" <-- difference between ON and OFF");
  Serial.println();
}

void welcome() {
  Serial.println("Press the green button.");
}