/*
   Project:       Break-beam Timer
   Description:   Measure the time it takes for an
                  object to travel from A to B.
                  "j" triggers Start, "k" triggers the "IR beam"
   Creation date: 10/23/23
   Author:        AnonEngineering

   From a question by:
                 ichiko aoba's cat
                 Discord Arduino #coding-help 10/23/23 6:13PM

   License: https://en.wikipedia.org/wiki/Beerware
*/

#include <Servo.h>

const int SERVO_PIN = 3;
const int BTN_PIN = 5;
const int IR_PIN = 4;
const int CLOSE_ANGLE = 0;
const int OPEN_ANGLE = 180;
const unsigned long RELEASE_DELAY = 10;

Servo gateServo;  // create servo object

bool checkButton()  {
  static bool oldBtnState = true; // INPUT_PULLUP idles high
  bool isButtonPressed = false;
  int btnState = digitalRead(BTN_PIN);
  if (btnState != oldBtnState)  { // if the button changed
    oldBtnState = btnState;       // remember new state
    if (btnState == LOW)  {       // and it's now LOW
      isButtonPressed = true;
      //Serial.println("Button pressed");
    } else  {
      //Serial.println("Button released");
    }
    delay(20);  // for debounce
  }
  return isButtonPressed;
}

void checkIR()  {
  while (digitalRead(IR_PIN)) {
    // do nothing until the beam breaks
  };
}

void closeGate() {
  gateServo.write(CLOSE_ANGLE);
}

void openGate() {
  gateServo.write(OPEN_ANGLE);
}

void setup() {
  Serial.begin(9600);
  pinMode(BTN_PIN, INPUT_PULLUP);
  pinMode(IR_PIN, INPUT_PULLUP);
  gateServo.attach(SERVO_PIN);
  gateServo.write(CLOSE_ANGLE); // initial position
  delay(500);
  Serial.println("System ready");
}

void loop() {
  int btnState = checkButton();
  if (btnState) { // the button was pressed
    openGate();
    delay(RELEASE_DELAY); // mechanical gate delay
    unsigned long startTime = millis();
    checkIR();  // this function blocks until IR triggers
    unsigned long stopTime = millis();
    unsigned long duration = stopTime - startTime;
    Serial.print("Stop time:\t");
    Serial.print(stopTime);
    Serial.println(" ms");
    Serial.print("Start time:\t");
    Serial.print(startTime);
    Serial.println(" ms");
    Serial.print("Duration:\t");
    Serial.print(duration);
    Serial.println(" ms");
    Serial.println();
    closeGate();
    delay(500);
    Serial.println("System ready");
  }
}