source: OniSplit/Xml/GenericXmlWriter.cs@ 1162

using System;
using System.Collections.Generic;
using System.Globalization;
using System.Xml;
using Oni.Imaging;
using Oni.Metadata;

namespace Oni.Xml
{
    internal class GenericXmlWriter : IMetaTypeVisitor
    {
        private readonly Action<InstanceDescriptor> exportChild;
        private readonly XmlWriter xml;
        private readonly Stack<int> startOffsetStack;
        private InstanceFile instanceFile;
        private BinaryReader reader;

        public static void Write(XmlWriter xml, Action<InstanceDescriptor> exportChild, InstanceDescriptor descriptor)
        {
            var writer = new GenericXmlWriter(xml, exportChild);
            writer.WriteInstance(descriptor);
        }

        private GenericXmlWriter(XmlWriter xml, Action<InstanceDescriptor> exportChild)
        {
            this.exportChild = exportChild;
            this.xml = xml;
            this.startOffsetStack = new Stack<int>();
        }

        private void WriteInstance(InstanceDescriptor descriptor)
        {
            using (reader = descriptor.OpenRead())
            {
                BeginXmlInstance(descriptor);
                descriptor.Template.Type.Accept(this);
                EndXmlInstance();
            }
        }

        private void BeginXmlInstance(InstanceDescriptor descriptor)
        {
            instanceFile = descriptor.File;
            startOffsetStack.Push(reader.Position - 8);

            string tag = descriptor.Template.Tag.ToString();

            xml.WriteStartElement(tag);
            xml.WriteAttributeString("id", XmlConvert.ToString(descriptor.Index));
        }

        private void EndXmlInstance()
        {
            startOffsetStack.Pop();
            xml.WriteEndElement();
        }

        #region IMetaTypeVisitor Members

        void IMetaTypeVisitor.VisitEnum(MetaEnum type)
        {
            type.BinaryToXml(reader, xml);
        }

        void IMetaTypeVisitor.VisitByte(MetaByte type)
        {
            xml.WriteValue(reader.ReadByte());
        }

        void IMetaTypeVisitor.VisitInt16(MetaInt16 type)
        {
            xml.WriteValue(reader.ReadInt16());
        }

        void IMetaTypeVisitor.VisitUInt16(MetaUInt16 type)
        {
            xml.WriteValue(reader.ReadUInt16());
        }

        void IMetaTypeVisitor.VisitInt32(MetaInt32 type)
        {
            xml.WriteValue(reader.ReadInt32());
        }

        void IMetaTypeVisitor.VisitUInt32(MetaUInt32 type)
        {
            xml.WriteValue(reader.ReadUInt32());
        }

        void IMetaTypeVisitor.VisitInt64(MetaInt64 type)
        {
            xml.WriteValue(reader.ReadInt64());
        }

        void IMetaTypeVisitor.VisitUInt64(MetaUInt64 type)
        {
            xml.WriteValue(XmlConvert.ToString(reader.ReadUInt64()));
        }

        void IMetaTypeVisitor.VisitFloat(MetaFloat type)
        {
            xml.WriteValue(reader.ReadSingle());
        }

        void IMetaTypeVisitor.VisitVector2(MetaVector2 type)
        {
            xml.WriteFloatArray(reader.ReadSingleArray(2));
        }

        void IMetaTypeVisitor.VisitVector3(MetaVector3 type)
        {
            xml.WriteFloatArray(reader.ReadSingleArray(3));
        }

        void IMetaTypeVisitor.VisitMatrix4x3(MetaMatrix4x3 type)
        {
            xml.WriteFloatArray(reader.ReadSingleArray(12));
        }

        void IMetaTypeVisitor.VisitPlane(MetaPlane type)
        {
            xml.WriteFloatArray(reader.ReadSingleArray(4));
        }

        void IMetaTypeVisitor.VisitQuaternion(MetaQuaternion type)
        {
            xml.WriteFloatArray(reader.ReadSingleArray(4));
        }

        void IMetaTypeVisitor.VisitBoundingSphere(MetaBoundingSphere type)
        {
            WriteFields(type.Fields);
        }

        void IMetaTypeVisitor.VisitBoundingBox(MetaBoundingBox type)
        {
            WriteFields(type.Fields);
        }

        void IMetaTypeVisitor.VisitColor(MetaColor type)
        {
            Color color = reader.ReadColor();

            if (color.A == 255)
                xml.WriteValue(string.Format(CultureInfo.InvariantCulture, "{0} {1} {2}", color.R, color.G, color.B));
            else
                xml.WriteValue(string.Format(CultureInfo.InvariantCulture, "{0} {1} {2} {3}", color.R, color.G, color.B, color.A));
        }

        void IMetaTypeVisitor.VisitRawOffset(MetaRawOffset type)
        {
            xml.WriteValue(reader.ReadInt32());
        }

        void IMetaTypeVisitor.VisitSepOffset(MetaSepOffset type)
        {
            xml.WriteValue(reader.ReadInt32());
        }

        void IMetaTypeVisitor.VisitPointer(MetaPointer type)
        {
            int id = reader.ReadInt32();

            if (id == 0)
            {
                xml.WriteString(string.Empty);
                return;
            }

            exportChild(instanceFile.GetDescriptor(id));
        }

        void IMetaTypeVisitor.VisitString(MetaString type)
        {
            xml.WriteValue(reader.ReadString(type.Count));
        }

        void IMetaTypeVisitor.VisitPadding(MetaPadding type)
        {
            reader.Skip(type.Count);
        }

        void IMetaTypeVisitor.VisitStruct(MetaStruct type)
        {
            WriteFields(type.Fields);
        }

        void IMetaTypeVisitor.VisitArray(MetaArray type)
        {
            WriteArray(type.ElementType, type.Count);
        }

        void IMetaTypeVisitor.VisitVarArray(MetaVarArray type)
        {
            int count;

            if (type.CountField.Type == MetaType.Int16)
                count = reader.ReadInt16();
            else
                count = reader.ReadInt32();

            WriteArray(type.ElementType, count);
        }

        #endregion

        private void WriteFields(IEnumerable<Field> fields)
        {
            foreach (var field in fields)
            {
                if (field.Type is MetaPadding)
                {
                    field.Type.Accept(this);
                    continue;
                }

                string name = field.Name;

                if (string.IsNullOrEmpty(name))
                {
                    int fieldOffset = reader.Position - startOffsetStack.Peek();
                    name = string.Format(CultureInfo.InvariantCulture, "Offset_{0:X4}", fieldOffset);
                }

                xml.WriteStartElement(name);
                field.Type.Accept(this);
                xml.WriteEndElement();
            }
        }

        private void WriteArray(MetaType elementType, int count)
        {
            bool simpleArray = elementType.IsBlittable;
            simpleArray = false;

            for (int i = 0; i < count; i++)
            {
                startOffsetStack.Push(reader.Position);

                if (!simpleArray)
                    xml.WriteStartElement(elementType.Name);

                elementType.Accept(this);

                if (!simpleArray)
                    xml.WriteEndElement();
                else if (i != count - 1)
                    xml.WriteWhitespace(" \n");

                startOffsetStack.Pop();
            }
        }
    }
}