/*
  Hold a button for a period, when released prior to the period abort.

  Uses millis() to keep track of time (milliseconds)
  https://www.norwegiancreations.com/2017/09/arduino-tutorial-using-millis-instead-of-delay/

  Author: F. van Slooten
*/
#include <U8g2lib.h>

#define START_BTN 4

U8X8_SSD1306_128X64_NONAME_HW_I2C display(U8X8_PIN_NONE);

int period = 5000; // time to hold the button
unsigned long time_start = 0;
int status = 0; // 0: checking hold, 1: button succesfully holded, 2: aborted

void setup() {
  Serial.begin(9600);
  pinMode(START_BTN, INPUT_PULLUP); // start button, without resistor (internal pull-up)
  display.begin();
  display.setPowerSave(0);
  display.setFont(u8x8_font_pxplusibmcgathin_f);

  display.drawString(0, 0, "PRESS TO START");
  // wait until button pressed to proceed:
  // (this while statement halts the program, until the button is pressed)
  while (digitalRead(START_BTN) == HIGH) ; // note the empty statement: ';' does nothing, thus waits for START_BTN to be pressed (becomes LOW)
  display.clearLine(0);
  display.drawString(0, 0, "HOLD");
  time_start = millis(); // start time
  delay(200);
}

void loop() {
  if (status > 0) {
    return; // do nothing if status > 0
  }
  else { // status == 0, we are checking if the button is being held
    if (millis() >= time_start + period) { // holding period over?
      display.clearLine(0);
      display.drawString(0, 0, "DONE"); // time to hold the button for period succesfully done
      status = 1;
    }
    else if (digitalRead(START_BTN) == HIGH) { // button released?
      // abort, button was released
      display.clearLine(0);
      display.drawString(0, 0, "ABORT");
      status = 2;
    }
  }
}