RangeObserver

using System;

using UnityEngine;
using UnityEngine.Events;

public class RangeObserver : MonoBehaviour
{
    [SerializeField] private Range _range;
    [SerializeField] private Transform _target;
    [SerializeField] private RangeBoundary _boundary;

    public float Distance => Vector3.Distance(transform.position, Target.position);

    public UnityEvent<bool> Changed;

    private bool _value;

    public bool Value
    {
        get => _value;
        set
        {
            if (value != _value)
            {
                _value = value;
                Changed.Invoke(value);
            }
        }
    }

    public Transform Target { get => _target; set => _target = value; }

    private void Start() =>
        ResolveValue();

    private void ResolveValue()
    {
        switch (_boundary)
        {
            case RangeBoundary.In:
                Value = Distance.In(_range);
                break;
            case RangeBoundary.Out:
                Value = Distance.Out(_range);
                break;
        }
    }

    private void Update() =>
        Value = Distance.In(_range);
}

public enum RangeBoundary
{
    In,
    Out
}

[Serializable]
public struct Range
{
    [SerializeField] private float _min;
    [SerializeField] private float _max;

    public bool In(float value) =>
        _min <= value && value <= _max;

    public bool Out(float value) =>
        _min >= value || value >= _max;
}

public static class RangeExtensions
{
    public static bool In(this float value, Range range)
        => range.In(value);

    public static bool Out(this float value, Range range)
        => range.Out(value);
}