// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System.Reflection;
using System.Text;
using System.Windows.Markup;
 
 
namespace System.Windows
{
    /// <summary>
    ///  ThemeDictionaryExtension allows application authors to customize
    ///  control styles based on the current system theme.
    ///
    /// </summary>
    [MarkupExtensionReturnType(typeof(Uri))]
    public class ThemeDictionaryExtension : MarkupExtension
    {
        #region Constructors
 
        /// <summary>
        ///  Constructor that takes no parameters
        /// </summary>
        public ThemeDictionaryExtension()
        {
        }
 
        /// <summary>
        ///  Constructor that takes the name of the assembly that contains the themed ResourceDictionary.
        /// </summary>
        public ThemeDictionaryExtension(string assemblyName)
        {
            ArgumentNullException.ThrowIfNull(assemblyName);
 
            _assemblyName = assemblyName;
        }
 
        #endregion 
 
        #region Public Properties
 
        /// <summary>
        ///     The name of the assembly that contains the themed ResourceDictionary.
        /// </summary>
        public string AssemblyName
        {
            get { return _assemblyName; }
            set { _assemblyName = value; }
        }
 
        #endregion
 
        #region Public Methods
 
        /// <summary>
        ///  Return an object that should be set on the targetObject's targetProperty
        ///  for this markup extension.  For ThemeDictionaryExtension, this is the Uri
        ///  pointing to theme specific dictionary in the specified assembly by AssemblyName.
        /// </summary>
        /// <param name="serviceProvider">ServiceProvider that can be queried for services.</param>
        /// <returns>
        ///  The object to set on this property.
        /// </returns>
        public override object ProvideValue(IServiceProvider serviceProvider)
        {
            if (string.IsNullOrEmpty(AssemblyName))
            {
                throw new InvalidOperationException(SR.ThemeDictionaryExtension_Name);
            }
 
            IProvideValueTarget provideValueTarget = serviceProvider.GetService(typeof(IProvideValueTarget)) as IProvideValueTarget;
            if( provideValueTarget == null )
            {
                throw new InvalidOperationException(SR.Format(SR.MarkupExtensionNoContext, GetType().Name, "IProvideValueTarget" ));
            }
                
            object targetObject = provideValueTarget.TargetObject;
            object targetProperty = provideValueTarget.TargetProperty;
 
            ResourceDictionary dictionary = targetObject as ResourceDictionary;
            PropertyInfo propertyInfo = targetProperty as PropertyInfo;
 
            // Allow targetProperty to be null or ResourceDictionary.Source
            if (dictionary == null || (targetProperty != null && propertyInfo != SourceProperty))
            {
                throw new InvalidOperationException(SR.ThemeDictionaryExtension_Source);
            }
 
            Register(dictionary, _assemblyName);
            dictionary.IsSourcedFromThemeDictionary = true;
 
            return GenerateUri(_assemblyName, SystemResources.ResourceDictionaries.ThemedResourceName, MS.Win32.UxThemeWrapper.ThemeName);
        }
 
        // Build the Uri for the assembly:
        // /AssemblyName;Component/themes/<CurrentTheme>.<Color>.xaml
        private static Uri GenerateUri(string assemblyName, string resourceName, ReadOnlySpan<char> themeName)
        {
            StringBuilder uri = new StringBuilder(assemblyName.Length + 50);
 
            uri.Append('/');
            uri.Append(assemblyName);
 
            // If assembly is PresentationFramework, append the Theme name
            if (assemblyName.Equals(SystemResources.PresentationFrameworkName, StringComparison.OrdinalIgnoreCase))
            {
                uri.Append('.');
                uri.Append(themeName);
            }
 
            uri.Append(";component/");
            uri.Append(resourceName);
            uri.Append(".xaml");
 
            return new Uri(uri.ToString(), System.UriKind.RelativeOrAbsolute);
        }
 
        internal static Uri GenerateFallbackUri(ResourceDictionary dictionary, string resourceName)
        {
            Span<Range> splitRegions = stackalloc Range[3];
            for (int i = 0; i < _themeDictionaryInfos.Count; i++)
            {
                ThemeDictionaryInfo info = _themeDictionaryInfos[i];
 
                if (!info.DictionaryReference.IsAlive)
                {
                    // Remove from list
                    _themeDictionaryInfos.RemoveAt(i);
                    i--;
                    continue;
                }
                if ((ResourceDictionary)info.DictionaryReference.Target == dictionary)
                {
                    ReadOnlySpan<char> nameSpan = resourceName.AsSpan();
                    if (nameSpan.Split(splitRegions, '/') < 2)
                        throw new IndexOutOfRangeException();
 
                    return GenerateUri(info.AssemblyName, resourceName, nameSpan[splitRegions[1]]);
                }
            }
            return null;
        }
 
 
        #endregion
 
        #region Data
 
        private string _assemblyName;
 
        #endregion
 
        #region Static Data
 
        // Keep track of all dictionaries that have ThemeDictionaryExtensions applied to them
        // When the theme changes update the Source uri to point to the new theme info
 
        // This is the ResourceDictionary.Source property info
        private static PropertyInfo _sourceProperty;
 
        private static PropertyInfo SourceProperty
        {
            get
            {
                if (_sourceProperty == null)
                {
                    _sourceProperty = typeof(ResourceDictionary).GetProperty("Source");
                }
                return _sourceProperty;
            }
        }
 
        private class ThemeDictionaryInfo
        {
            public WeakReference DictionaryReference;
            public string AssemblyName;
        }
 
        // Store a list of dictionaries and assembly info's.
        // When the theme changes, give the dictionaries a new Source Uri
 
        [ThreadStatic]
        private static List<ThemeDictionaryInfo> _themeDictionaryInfos;
 
        private static void Register(ResourceDictionary dictionary, string assemblyName)
        {
            Debug.Assert(dictionary != null, "dictionary should not be null");
            Debug.Assert(assemblyName != null, "assemblyName should not be null");
 
            if (_themeDictionaryInfos == null)
            {
                _themeDictionaryInfos = new List<ThemeDictionaryInfo>();
            }
            ThemeDictionaryInfo info;
            
            for (int i = 0; i < _themeDictionaryInfos.Count; i++)
            {
                info = _themeDictionaryInfos[i];
 
                if (!info.DictionaryReference.IsAlive)
                {
                    // Remove from list
                    _themeDictionaryInfos.RemoveAt(i);
                    i--;
                    continue;
                }
 
                if (info.DictionaryReference.Target == dictionary)
                {
                    info.AssemblyName = assemblyName;
                    return;
                }
            }
 
            // Not present, add to list
            info = new ThemeDictionaryInfo
            {
                DictionaryReference = new WeakReference(dictionary),
                AssemblyName = assemblyName
            };
 
            _themeDictionaryInfos.Add(info);
            
        }
 
        internal static void OnThemeChanged()
        {
            // Update all resource dictionaries
 
            if (_themeDictionaryInfos != null)
            {
                for (int i = 0; i < _themeDictionaryInfos.Count; i++)
                {
                    ThemeDictionaryInfo info = _themeDictionaryInfos[i];
 
                    if (!info.DictionaryReference.IsAlive)
                    {
                        // Remove from list
                        _themeDictionaryInfos.RemoveAt(i);
                        i--;
                        continue;
                    }
 
                    // Provide the new dictionary URI
                    ResourceDictionary dictionary = (ResourceDictionary)info.DictionaryReference.Target;
                    dictionary.Source = GenerateUri(info.AssemblyName, SystemResources.ResourceDictionaries.ThemedResourceName, MS.Win32.UxThemeWrapper.ThemeName);
                }
            }
        }
 
        #endregion
    }
}