// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System.Collections.Generic;
using System.IO;
using System.Xml;
 
namespace System.ServiceModel
{
    internal sealed class XmlBuffer
    {
        private readonly List<Section> _sections;
        private byte[] _buffer;
        private int _offset;
        private BufferedStream _stream;
        private BufferState _bufferState;
        private XmlDictionaryWriter _writer;
        private XmlDictionaryReaderQuotas _quotas;
 
        private enum BufferState
        {
            Created,
            Writing,
            Reading,
        }
 
        private struct Section
        {
            public Section(int offset, int size, XmlDictionaryReaderQuotas quotas)
            {
                Offset = offset;
                Size = size;
                Quotas = quotas;
            }
 
            public int Offset { get; }
 
            public int Size { get; }
 
            public XmlDictionaryReaderQuotas Quotas { get; }
        }
 
        public XmlBuffer(int maxBufferSize)
        {
            if (maxBufferSize < 0)
                throw new ArgumentOutOfRangeException(nameof(maxBufferSize), maxBufferSize, SR.ValueMustBeNonNegative);
 
            int initialBufferSize = Math.Min(512, maxBufferSize);
            _stream = new BufferedStream(new MemoryStream(), initialBufferSize);
            _sections = new List<Section>(1);
        }
 
        public int BufferSize => _buffer.Length;
 
        public int SectionCount => _sections.Count;
 
        public XmlDictionaryWriter OpenSection(XmlDictionaryReaderQuotas quotas)
        {
            if (_bufferState != BufferState.Created)
                throw CreateInvalidStateException();
            _bufferState = BufferState.Writing;
            _quotas = new XmlDictionaryReaderQuotas();
            quotas.CopyTo(_quotas);
 
            _writer = XmlDictionaryWriter.CreateBinaryWriter(_stream, null, null, false);
 
            return _writer;
        }
 
        public void CloseSection()
        {
            if (_bufferState != BufferState.Writing)
                throw CreateInvalidStateException();
            _writer.Close();
            _bufferState = BufferState.Created;
 
            int size = (int)_stream.Length - _offset;
            _sections.Add(new Section(_offset, size, _quotas));
            _offset += size;
        }
 
        public void Close()
        {
            if (_bufferState != BufferState.Created)
                throw CreateInvalidStateException();
            _bufferState = BufferState.Reading;
            _buffer = new byte[_stream.Length];
            _stream.Position = 0;
 
#if NET
            _stream.ReadExactly(_buffer);
#else
            int totalRead = 0;
            while (totalRead < _buffer.Length)
            {
                int bytesRead = _stream.Read(_buffer, totalRead, _buffer.Length - totalRead);
                if (bytesRead <= 0)
                {
                    throw new EndOfStreamException();
                }
                totalRead += bytesRead;
            }
#endif
 
            _writer = null;
            _stream = null;
        }
 
        private static InvalidOperationException CreateInvalidStateException() => new InvalidOperationException(SR.XmlBufferInInvalidState);
 
        public XmlDictionaryReader GetReader(int sectionIndex)
        {
            if (_bufferState != BufferState.Reading)
                throw CreateInvalidStateException();
            Section section = _sections[sectionIndex];
            XmlDictionaryReader reader = XmlDictionaryReader.CreateBinaryReader(_buffer, section.Offset, section.Size, null, section.Quotas, null, null);
 
            reader.MoveToContent();
            return reader;
        }
 
        public void WriteTo(int sectionIndex, XmlWriter writer)
        {
            if (_bufferState != BufferState.Reading)
                throw CreateInvalidStateException();
            XmlDictionaryReader reader = GetReader(sectionIndex);
            try
            {
                writer.WriteNode(reader, false);
            }
            finally
            {
                reader.Close();
            }
        }
    }
}