// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
 
using System;
using System.Collections.Immutable;
using System.Globalization;
using System.IO;
using System.Linq;
using System.Xml;
using System.Xml.Linq;
using Microsoft.VisualStudio.Shell.Interop;
using Roslyn.Utilities;
 
namespace Microsoft.CodeAnalysis.ColorSchemes
{
    internal partial class ColorSchemeApplier
    {
        private static class ColorSchemeReader
        {
            private static readonly XmlReaderSettings s_xmlSettings = new() { DtdProcessing = DtdProcessing.Prohibit };
            private const string RawColorType = nameof(__VSCOLORTYPE.CT_RAW);
            private const string SystemColorType = nameof(__VSCOLORTYPE.CT_SYSCOLOR);
 
            public static ColorScheme ReadColorScheme(Stream schemeStream)
            {
                using var xmlReader = XmlReader.Create(schemeStream, s_xmlSettings);
                var schemeDocument = XDocument.Load(xmlReader);
 
                var themes = schemeDocument
                    .Descendants("Theme")
                    .Select(ReadColorTheme);
 
                return new ColorScheme(themes.ToImmutableArray());
            }
 
            private static ColorTheme ReadColorTheme(XElement themeElement)
            {
                var themeName = (string)themeElement.Attribute("Name");
                var themeGuid = Guid.Parse((string)themeElement.Attribute("GUID"));
 
                var categoryElement = themeElement.Descendants("Category").Single();
                var category = ReadColorCategory(categoryElement);
 
                return new ColorTheme(themeName, themeGuid, category);
            }
 
            private static ColorCategory ReadColorCategory(XElement categoryElement)
            {
                var categoryName = (string)categoryElement.Attribute("Name");
                var categoryGuid = Guid.Parse((string)categoryElement.Attribute("GUID"));
 
                var colorItems = categoryElement
                    .Descendants("Color")
                    .Select(ReadColorItem)
                    .WhereNotNull();
 
                return new ColorCategory(categoryName, categoryGuid, colorItems.ToImmutableArray());
            }
 
            private static ColorItem? ReadColorItem(XElement colorElement)
            {
                var name = (string)colorElement.Attribute("Name");
 
                var backgroundElement = colorElement.Descendants("Background").SingleOrDefault();
                (var backgroundType, var backgroundColor) = backgroundElement is object
                    ? ReadColor(backgroundElement)
                    : (__VSCOLORTYPE.CT_INVALID, (uint?)null);
 
                var foregroundElement = colorElement.Descendants("Foreground").SingleOrDefault();
                (var foregroundType, var foregroundColor) = foregroundElement is object
                    ? ReadColor(foregroundElement)
                    : (__VSCOLORTYPE.CT_INVALID, (uint?)null);
 
                if (backgroundElement is null && foregroundElement is null)
                {
                    return null;
                }
 
                return new ColorItem(name, backgroundType, backgroundColor, foregroundType, foregroundColor);
            }
 
            private static (__VSCOLORTYPE Type, uint Color) ReadColor(XElement colorElement)
            {
                var colorType = (string)colorElement.Attribute("Type");
                var sourceColor = (string)colorElement.Attribute("Source");
 
                __VSCOLORTYPE type;
                uint color;
 
                if (colorType == RawColorType)
                {
                    type = __VSCOLORTYPE.CT_RAW;
 
                    // The ColorableItemInfo returned by the FontAndColorStorage retuns RGB color information as 0x00BBGGRR.
                    // Optimize for color comparisons by converting ARGB to BGR by ignoring the alpha channel and reversing byte order.
                    var r = sourceColor.Substring(2, 2);
                    var g = sourceColor.Substring(4, 2);
                    var b = sourceColor.Substring(6, 2);
                    color = uint.Parse($"{b}{g}{r}", NumberStyles.HexNumber);
                }
                else if (colorType == SystemColorType)
                {
                    type = __VSCOLORTYPE.CT_SYSCOLOR;
 
                    color = uint.Parse(sourceColor, NumberStyles.HexNumber);
                }
                else
                {
                    throw ExceptionUtilities.UnexpectedValue(colorType);
                }
 
                return (type, color);
            }
        }
    }
}