HandyControl/src/Shared/HandyControl_Shared/Themes/Theme.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Windows;
using System.Windows.Media;
using HandyControl.Data;
using HandyControl.Tools;
using HandyControl.Tools.Helper;
using HandyControl.Tools.Interop;
using Microsoft.Win32;

namespace HandyControl.Themes
{
    public class Theme : ResourceDictionary
    {
        public Theme()
        {
            if (DesignerHelper.IsInDesignMode)
            {
                MergedDictionaries.Add(ResourceHelper.GetSkin(SkinType.Default));
                MergedDictionaries.Add(ResourceHelper.GetTheme());
            }
            else
            {
                InitResource();
            }
        }

        #region Skin

        private SkinType _manualSkinType;

        private SkinType _skin;

        public virtual SkinType Skin
        {
            get => _skin;
            set
            {
                if (_skin == value) return;
                _skin = value;

                UpdateSkin();
            }
        }

        public static readonly DependencyProperty SkinProperty = DependencyProperty.RegisterAttached(
            "Skin", typeof(SkinType), typeof(Theme), new PropertyMetadata(default(SkinType), OnSkinChanged));

        private static void OnSkinChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            if (d is not FrameworkElement element)
            {
                return;
            }

            var skin = (SkinType) e.NewValue;

            var themes = new List<Theme>();
            GetAllThemes(element.Resources, ref themes);

            if (themes.Count > 0)
            {
                foreach (var theme in themes)
                {
                    theme.Skin = skin;
                }
            }
            else
            {
                element.Resources.MergedDictionaries.Add(new Theme
                {
                    Skin = skin
                });
            }
        }

        private static void GetAllThemes(ResourceDictionary resourceDictionary, ref List<Theme> themes)
        {
            if (resourceDictionary is Theme theme)
            {
                themes.Add(theme);
            }

            // we must consider it's MergedDictionaries
            foreach (var dictionaryMergedDictionary in resourceDictionary.MergedDictionaries)
            {
                GetAllThemes(dictionaryMergedDictionary, ref themes);
            }
        }

        public static void SetSkin(DependencyObject element, SkinType value)
            => element.SetValue(SkinProperty, value);

        public static SkinType GetSkin(DependencyObject element)
            => (SkinType) element.GetValue(SkinProperty);

        #endregion

        #region SyncWithSystem

        private bool _syncWithSystem;

        public bool SyncWithSystem
        {
            get => _syncWithSystem;
            set
            {
                _syncWithSystem = value;

                if (value)
                {
                    _manualSkinType = _skin;
                    SyncWithSystemTheme();

                    SystemEvents.UserPreferenceChanged += SystemEvents_UserPreferenceChanged;
                }
                else
                {
                    SystemEvents.UserPreferenceChanged -= SystemEvents_UserPreferenceChanged;

                    _skin = _manualSkinType;
                    UpdateSkin();
                }
            }
        }

        private void SystemEvents_UserPreferenceChanged(object sender, UserPreferenceChangedEventArgs e)
        {
            if (e.Category == UserPreferenceCategory.General)
            {
                SyncWithSystemTheme();
            }
        }

        private void SyncWithSystemTheme()
        {
            _skin = SystemHelper.DetermineIfInLightThemeMode() ? SkinType.Default : SkinType.Dark;
            UpdateSkin();
        }

        #endregion

        #region AccentColor

        private Color? _accentColor;

        public Color? AccentColor
        {
            get => _accentColor;
            set
            {
                _accentColor = value;

                if (value == null)
                {
                    _precSkin = null;
                }

                UpdateSkin();
            }
        }

        #endregion

        #region Source

        private Uri _source;

        public new Uri Source
        {
            get => DesignerHelper.IsInDesignMode ? null : _source;
            set => _source = value;
        }

        #endregion

        public string Name { get; set; }

        private SkinType _prevSkinType;

        private ResourceDictionary _precSkin;

        public virtual ResourceDictionary GetSkin(SkinType skinType)
        {
            if (_precSkin == null || _prevSkinType != skinType)
            {
                _precSkin = ResourceHelper.GetSkin(skinType);
                _prevSkinType = skinType;
            }

            if (!SyncWithSystem)
            {
                if (AccentColor != null)
                {
                    UpdateAccentColor(AccentColor.Value);
                }
            }
            else
            {
                InteropMethods.DwmGetColorizationColor(out var color, out _);
                UpdateAccentColor(ColorHelper.ToColor(color));
            }

            return _precSkin;
        }

        public static Theme GetTheme(string name, ResourceDictionary resourceDictionary)
        {
            if (string.IsNullOrEmpty(name) || resourceDictionary == null)
            {
                return null;
            }

            return resourceDictionary.MergedDictionaries.OfType<Theme>().FirstOrDefault(item => Equals(item.Name, name));
        }

        public virtual ResourceDictionary GetTheme() => ResourceHelper.GetTheme();

        private void InitResource()
        {
            if (DesignerHelper.IsInDesignMode)
            {
                return;
            }

            MergedDictionaries.Clear();
            MergedDictionaries.Add(GetSkin(Skin));
            MergedDictionaries.Add(GetTheme());
        }

        private void UpdateAccentColor(Color color)
        {
            _precSkin[ResourceToken.PrimaryColor] = color;
            _precSkin[ResourceToken.DarkPrimaryColor] = color;
            _precSkin[ResourceToken.TitleColor] = color;
            _precSkin[ResourceToken.SecondaryTitleColor] = color;
        }

        private void UpdateSkin() => MergedDictionaries[0] = GetSkin(Skin);
    }

    public class StandaloneTheme : Theme
    {
        public override ResourceDictionary GetTheme() => ResourceHelper.GetStandaloneTheme();
    }
}