// <copyright file="MemoryStreamVisualizerObjectSource.cs" company="PlaceholderCompany">
// Copyright (c) PlaceholderCompany. All rights reserved.
// </copyright>

namespace MemoryStreamObjectSource;

using Microsoft.VisualStudio.DebuggerVisualizers;
using System.IO;

/// <summary>
/// Object source class for the MemoryStreamVisualizer.
/// </summary>
public class MemoryStreamVisualizerObjectSource : VisualizerObjectSource
{
    /// <summary>
    /// How many rows will be transfered, at most, responding to a single request.
    /// </summary>
    public const int RowsCountPerRequest = 1024;

    /// <summary>
    /// How many bytes will be transfered for each row.
    /// </summary>
    public const int RowLength = 16;

    /// <inheritdoc/>
    public override void TransferData(object target, Stream incomingData, Stream outgoingData)
    {
        if (target is not MemoryStream memoryStream)
        {
            return;
        }


        using BinaryReader binaryReader = new(incomingData);
        var index = binaryReader.ReadInt32(); // The extension will send the offset (Int32) to start reading from

        using BinaryWriter binaryWriter = new(outgoingData);
        var backupPosition = memoryStream.Position;

        // Will reply with the current MemoryStream.Position (Int64),
        // followed by MemoryStream.Length (Int64),
        // followed by up to 16KB of data retrieved from the MemoryStream
        binaryWriter.Write(backupPosition);
        binaryWriter.Write(memoryStream.Length);
        if (index < memoryStream.Length)
        {
            try
            {
                var data = new byte[RowsCountPerRequest * RowLength];
                memoryStream.Seek(index, SeekOrigin.Begin);
                var count = memoryStream.Read(data, 0, data.Length);
                binaryWriter.Write(data, 0, count);
            }
            finally
            {
                // Make sure to restore the MemoryStream to its original position
                memoryStream.Seek(backupPosition, SeekOrigin.Begin);
            }
        }

        binaryWriter.Flush();

    }
}