CoroutineTest

using System;
using System.Collections;

using UnityEngine;
using UnityEngine.InputSystem;
using UnityEngine.UI;

public class CoroutineTest : MonoBehaviour
{
    public Image BarImage;
    private Coroutine _fillAmountCoroutine = null;

    [SerializeField] private float _decreaseStep = 0.2f;
    [SerializeField] private float _defaultEndValue = 1f;
    private float _endValue = 1f;

    private void Start()
    {
        ResetEndValue();
    }

    public void ResetEndValue()
    {
        _endValue = _defaultEndValue;
    }

    private void Update()
    {
        if (Mouse.current.leftButton.wasPressedThisFrame)
        {
            if (_fillAmountCoroutine != null)
                StopCoroutine(_fillAmountCoroutine);

            IEnumerator doFillAmount = DoFillAmount(BarImage, 0f, _endValue, 1f);

            _fillAmountCoroutine = StartCoroutine(doFillAmount);

            _endValue -= _decreaseStep;

            if (_endValue <= 0)
                ResetEndValue();
        }
    }

    private IEnumerator DoFillAmount(Image image, float start, float end, float duration)
    {
        float elapsed = 0.0f;
        while (elapsed < duration)
        {
            image.fillAmount = Mathf.Lerp(start, end, elapsed / duration);
            elapsed += Time.deltaTime;
            yield return null;
        }

        image.fillAmount = end;
    }
}