riversong-code-showcase/Source/Riversong/Game/UI/DayNightUIThemeSystem.cs

using System;
using System.Collections.Generic;
using System.Reflection;
using Cysharp.Threading.Tasks;
using UnityEngine;
using UnityEngine.UIElements;

namespace DanieleMarotta.RiversongCodeShowcase
{
    [GameSystemGroup(typeof(UISystemGroup))]
    [InitializeAfter(typeof(UIInitializationSystem))]
    public class DayNightUIThemeSystem : GameSystem, IInitializable, IDisposable, IUpdatable
    {
        [InjectService]
        private GameConfig _config;

        [InjectService]
        private UIService _uiService;

        [InjectService]
        private World _world;

        private VisualElement _root;

        private RuntimeThemeSheet _runtimeThemeSheet;

        private float _lastAppliedNightBlend = -1;

        private bool _refreshClassEnabled;

        public DayNightUIThemeSystem(IServiceLocator serviceLocator) : base(serviceLocator)
        {
        }

        public UniTask InitializeAsync()
        {
            _root = _uiService.UIRoot.RootVisualElement;
            _runtimeThemeSheet = RuntimeThemeSheet.TryCreate(_root, _config.UI.Theme);

            ApplyTheme(true);

            return UniTask.CompletedTask;
        }

        public void Update()
        {
            ApplyTheme();
        }

        public void Dispose()
        {
            if (_root == null || _runtimeThemeSheet == null) return;

            _runtimeThemeSheet.Apply(0);
            ToggleRefreshClass();
            _lastAppliedNightBlend = 0;
        }

        private void ApplyTheme(bool force = false)
        {
            if (_root == null || _config.UI.Theme == null || _runtimeThemeSheet == null) return;

            var nightBlend = _world.TimeState.NightBlend;
            if (!force && !Application.isEditor && Mathf.Approximately(nightBlend, _lastAppliedNightBlend)) return;

            _runtimeThemeSheet.Apply(nightBlend);
            ToggleRefreshClass();

            _lastAppliedNightBlend = nightBlend;
        }

        private void ToggleRefreshClass()
        {
            _refreshClassEnabled = !_refreshClassEnabled;
            _root.EnableInClassList(RuntimeThemeSheet.RefreshClassName, _refreshClassEnabled);
        }

        private sealed class RuntimeThemeSheet
        {
            public const string RefreshClassName = "__day-night-theme-refresh";

            private readonly StyleSheet _styleSheet;

            private readonly RuntimePropertyBinding[] _bindings;

            private RuntimeThemeSheet(StyleSheet styleSheet, RuntimePropertyBinding[] bindings)
            {
                _styleSheet = styleSheet;
                _bindings = bindings;
            }

            public static RuntimeThemeSheet TryCreate(VisualElement root, DayNightUITheme theme)
            {
                if (root == null || theme == null) return null;

                var styleSheets = StyleSheetReflection.GetStyleSheets(root);
                if (styleSheets == null) return null;

                foreach (var styleSheet in styleSheets)
                {
                    if (!StyleSheetReflection.TryCreateBindings(styleSheet, theme.OrderedProperties, out var bindings)) continue;

                    return new RuntimeThemeSheet(styleSheet, bindings);
                }

                return null;
            }

            public void Apply(float nightBlend)
            {
                foreach (var binding in _bindings) binding.Apply(nightBlend);

                _styleSheet.contentHash = unchecked(_styleSheet.contentHash + 1);
            }
        }

        private sealed class RuntimePropertyBinding
        {
            private readonly DayNightUITheme.ThemeColorProperty _themeProperty;

            private readonly object _manipulator;

            private readonly object[] _setColorArguments = new object[2];

            public RuntimePropertyBinding(DayNightUITheme.ThemeColorProperty themeProperty, object manipulator)
            {
                _themeProperty = themeProperty;
                _manipulator = manipulator;
            }

            public void Apply(float nightBlend)
            {
                _setColorArguments[0] = 0;
                _setColorArguments[1] = Color.Lerp(_themeProperty.DayColor, _themeProperty.NightColor, nightBlend);
                StyleSheetReflection.SetColor(_manipulator, _setColorArguments);
            }
        }

        private static class StyleSheetReflection
        {
            private static readonly FieldInfo VisualElementStyleSheetListField = typeof(VisualElement).GetField("styleSheetList", BindingFlags.Instance | BindingFlags.NonPublic);

            private static readonly FieldInfo StyleSheetRulesField = typeof(StyleSheet).GetField("m_Rules", BindingFlags.Instance | BindingFlags.NonPublic);

            private static readonly Type StyleRuleType = StyleSheetRulesField?.FieldType.GetElementType();

            private static readonly MethodInfo StyleRuleGetPropertiesMethod = StyleRuleType?.GetMethod("get_properties", BindingFlags.Instance | BindingFlags.Public);

            private static readonly Type StylePropertyType = StyleRuleGetPropertiesMethod?.ReturnType.GetElementType();

            private static readonly MethodInfo StylePropertyGetNameMethod = StylePropertyType?.GetMethod("get_name", BindingFlags.Instance | BindingFlags.Public);

            private static readonly MethodInfo StylePropertyGetManipulatorMethod = StylePropertyType?.GetMethod("GetManipulator", BindingFlags.Instance | BindingFlags.NonPublic);

            private static readonly Type ManipulatorType = StylePropertyGetManipulatorMethod?.ReturnType;

            private static readonly MethodInfo ManipulatorSetColorMethod = ManipulatorType?.GetMethod(
                "SetColor",
                BindingFlags.Instance | BindingFlags.Public,
                null,
                new[]
                {
                    typeof(int),
                    typeof(Color)
                },
                null);

            public static List<StyleSheet> GetStyleSheets(VisualElement root)
            {
                return VisualElementStyleSheetListField?.GetValue(root) as List<StyleSheet>;
            }

            public static void SetColor(object manipulator, object[] arguments)
            {
                ManipulatorSetColorMethod?.Invoke(manipulator, arguments);
            }

            public static bool TryCreateBindings(StyleSheet styleSheet, IReadOnlyList<DayNightUITheme.ThemeColorProperty> themeProperties, out RuntimePropertyBinding[] bindings)
            {
                bindings = null;
                if (styleSheet == null || themeProperties == null) return false;
                if (StyleSheetRulesField == null ||
                    StyleRuleGetPropertiesMethod == null ||
                    StylePropertyGetNameMethod == null ||
                    StylePropertyGetManipulatorMethod == null ||
                    ManipulatorSetColorMethod == null)
                    return false;

                var propertiesByName = new Dictionary<string, object>(themeProperties.Count, StringComparer.Ordinal);
                var rules = StyleSheetRulesField.GetValue(styleSheet) as Array;
                if (rules == null) return false;

                foreach (var rule in rules)
                {
                    if (rule == null) continue;

                    var styleProperties = StyleRuleGetPropertiesMethod.Invoke(rule, null) as Array;
                    if (styleProperties == null) continue;

                    foreach (var styleProperty in styleProperties)
                    {
                        if (styleProperty == null) continue;

                        var propertyName = StylePropertyGetNameMethod.Invoke(styleProperty, null) as string;
                        if (string.IsNullOrEmpty(propertyName)) continue;
                        if (propertiesByName.ContainsKey(propertyName)) continue;

                        propertiesByName[propertyName] = styleProperty;
                    }
                }

                var resolvedBindings = new RuntimePropertyBinding[themeProperties.Count];

                for (var i = 0; i < themeProperties.Count; i++)
                {
                    var themeProperty = themeProperties[i];
                    if (!propertiesByName.TryGetValue(themeProperty.Name, out var styleProperty)) return false;

                    var manipulator = StylePropertyGetManipulatorMethod.Invoke(styleProperty, new object[] { styleSheet });
                    resolvedBindings[i] = new RuntimePropertyBinding(themeProperty, manipulator);
                }

                bindings = resolvedBindings;
                return true;
            }
        }
    }
}