// https://wokwi.com/projects/372337626147389441
// https://forum.arduino.cc/t/make-an-output-pin-behave-like-a-monostable-multivibrator/1155428/12


// this is meant to be the state diagram in post #12 
// the PIR delayTime is set to 2 seconds in the *.json file

# define IR_Pin   2
# define LED_Pin  13

// just to see that we are looping.
# define heartBeatLED_Pin 12

enum {IDOL = 0, LED_ON, LED_OFF, WAIT,};
  
unsigned long timer;

# define LED_ON_TIME  5000
# define NO_OBSTAKLE_WAIT_TIME 2000

void setup() {
  Serial.begin(115200);
  Serial.println("Hello World!\n");

  pinMode(IR_Pin, INPUT);
  pinMode(LED_Pin, OUTPUT);
  pinMode(heartBeatLED_Pin, OUTPUT);
}

byte state = IDOL;
bool irActive;
unsigned long now;

bool ledOn;

void loop() {
  delay(50);

  digitalWrite(heartBeatLED_Pin, (millis() & 512) ? HIGH : LOW);

// I. inputs to the model - time and motion activity
  now = millis();
  irActive = digitalRead(IR_Pin) == HIGH;

// P. process the inputs given the current state and inputs
  theFSM();

// O. use the process to set the outputs.
  digitalWrite(LED_Pin, ledOn ? HIGH : LOW);
}

void theFSM() {
  long elapsedTime = 0;

  switch (state) {
  case IDOL :
    if (irActive) {
      Serial.println("A. motion turns LED on");
      state = LED_ON;
      timer = now;
    }
    break;

  case LED_ON :
    ledOn = true;
    elapsedTime = now - timer;
    if (elapsedTime >= LED_ON_TIME) {
      Serial.println("B. time turns LED off");
      ledOn = false;
      state = LED_OFF;
    }
    break;

  case LED_OFF :
    if (!irActive) {
      Serial.println("C. IR signal gone, so");
      timer = now;
      state = WAIT;
    }
    break;

  case WAIT :
    elapsedTime = now - timer;
    if (irActive) {
      Serial.println("D. IR signal still or again, so");
      timer = now;
      state = WAIT;
    }
    else if (elapsedTime >= NO_OBSTAKLE_WAIT_TIME) {
      Serial.println("E. after a bit more time, we reset");
      timer = now;
      state = IDOL;
    }
    break;
  }
}