canto/Assets/Scripts/Editor/Drawers/DrawIfPropertyDrawer.cs

using System;
using System.Collections;
using KitsuneCafe.Sys.Attributes;
using UnityEditor;
using UnityEditor.UIElements;
using UnityEngine.UIElements;

namespace KitsuneCafe.Editor
{
  public abstract class ConditionalElement : VisualElement
  {
    protected SerializedProperty property;
    protected SerializedProperty comparedProperty;

    public ConditionalElement(SerializedProperty property, SerializedProperty comparedProperty)
    {
      this.property = property;
      this.comparedProperty = comparedProperty;

      if (property.propertyType == SerializedPropertyType.Generic)
      {
        IEnumerator children = property.GetEnumerator();

        while (children.MoveNext())
        {
          Add(new PropertyField(children.Current as SerializedProperty));
        }
      }
      else
      {
        Add(new PropertyField(property));
      }

      this.TrackPropertyValue(comparedProperty, OnPropertyValueChanged);
      schedule.Execute(() => OnPropertyValueChanged(comparedProperty));
    }

    protected void OnPropertyValueChanged(SerializedProperty property)
    {
      style.display = ShouldRender(property) ? DisplayStyle.Flex : DisplayStyle.None;
    }

    protected abstract bool ShouldRender(SerializedProperty property);
  }

  public class ConditionalBool : ConditionalElement
  {
    private readonly bool value;

    public ConditionalBool(
      SerializedProperty property,
      SerializedProperty comparedProperty,
      bool value
    ) : base(property, comparedProperty)
    {
      this.value = value;
    }

    protected override bool ShouldRender(SerializedProperty property)
    {
      return property.boolValue == value;
    }
  }

  public class ConditionalInt : ConditionalElement
  {
    private readonly int value;
    private readonly bool isFlagEnum;

    public ConditionalInt(
      SerializedProperty property,
      SerializedProperty comparedProperty,
      int value,
      bool isFlagEnum = false
    ) : base(property, comparedProperty)
    {
      this.value = value;
      this.isFlagEnum = isFlagEnum;
    }

    protected override bool ShouldRender(SerializedProperty property)
    {
      return isFlagEnum switch
      {
        true => (property.intValue & value) == value,
        false => property.intValue == value
      };
    }
  }

  [CustomPropertyDrawer(typeof(DrawIfAttribute))]
  public class DrawIfPropertyDrawer : PropertyDrawer
  {
    public override VisualElement CreatePropertyGUI(SerializedProperty property)
    {
      var drawIf = attribute as DrawIfAttribute;
      var comparedField = TryToFindSerializableProperty(drawIf.ComparedPropertyName, property);

      return comparedField.type switch
      {
        "bool" => new ConditionalBool(property, comparedField, (bool)drawIf.ComparedValue),
        "Enum" or "int" => new ConditionalInt(
          property,
          comparedField,
          (int)drawIf.ComparedValue,
          drawIf.IsEnumWithFlags
        ),
        _ => throw new NotImplementedException(),
      };
    }

    /// <summary>
    /// Return SerializedProperty by it's name if it exists, it works for nested objects and arrays
    /// </summary>
    /// <param name="propertyName"></param>
    /// <param name="property"></param>
    /// <returns></returns>
    private SerializedProperty TryToFindSerializableProperty(string propertyName, SerializedProperty property)
    {
      var serializedProperty = property.serializedObject.FindProperty(propertyName);

      if (serializedProperty == null)
      {
        string propertyPath = property.propertyPath;
        int idx = propertyPath.LastIndexOf('.');
        if (idx != -1)
        {
          propertyPath = propertyPath[..idx];
          return property.serializedObject.FindProperty(propertyPath).FindPropertyRelative(propertyName);
        }
      }

      return serializedProperty;
    }
  }
}