proto_racer/Assets/Scripts/LapTime.cs

using UnityEngine;

public class LapTime : MonoBehaviour
{
    public CheckPoint finishLine;
    public CheckPoint checkPoint1;
    public CheckPoint checkPoint2;
    public CheckPoint checkPoint3;

    private float _startTime = -1;
    private float _checkPoint1Time;
    private float _checkPoint2Time;
    private float _checkPoint3Time;
    private float _finishTime;
    private float _bestTime;

    public string GetTimeString()
    {
        return
            $"Sector 1: {_checkPoint1Time:F}\nSector 2: {_checkPoint2Time:F}\nSector 3: {_checkPoint3Time:F}\nLast Lap Time: {_finishTime:F}\nBest Lap: {_bestTime:F}";
    }
    
    // Start is called before the first frame update
    private void Start()
    {
        finishLine.CarPassed += FinishedLine;
        checkPoint1.CarPassed += CheckPoint1Passed;
        checkPoint2.CarPassed += CheckPoint2Passed;
        checkPoint3.CarPassed += CheckPoint3Passed;
        _bestTime = float.MaxValue;
        _finishTime = float.MaxValue;
    }

    private void CheckPoint1Passed()
    {
        _checkPoint1Time = Time.time - _startTime;
    }

    private void CheckPoint2Passed()
    {
        _checkPoint2Time = Time.time - _startTime - _checkPoint1Time;
    }

    private void CheckPoint3Passed()
    {
        _checkPoint3Time = Time.time - _startTime - _checkPoint2Time - _checkPoint1Time;
    }

    private void ResetTimers()
    {
        _startTime = Time.time;
        _checkPoint1Time = 0;
        _checkPoint2Time = 0;
        _checkPoint3Time = 0;
        if (_finishTime < _bestTime)
        {
            _bestTime = _finishTime;
        }
    }

    private void FinishedLine()
    {
        // make sure we didn't skip a checkpoint.
        if (_checkPoint1Time > 0 && _checkPoint2Time > 0 && _checkPoint3Time > 0)
        {
            // we finished
            _finishTime = Time.time - _startTime;
            ResetTimers();
        }
        else
        {
            ResetTimers();
        }
    }
}