// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System;
using System.Diagnostics;
using System.Linq;
using System.Runtime.InteropServices;
using System.Security.Cryptography;
using System.Text;
using Microsoft.Build.Framework;
using Microsoft.Build.Utilities;
using Newtonsoft.Json;

namespace Microsoft.DotNet.Build.Tasks.VisualStudio;

/// <summary>
/// Calculates Guid used in .pkgdef files for codeBase and bindingRedirect entries.
/// The implementation matches Microsoft.VisualStudio.Shell.ProvideDependentAssemblyAttribute.
/// </summary>
[MSBuildMultiThreadableTask]
public sealed class GetPkgDefAssemblyDependencyGuid : Task
{
    [Required]
    public ITaskItem[] Items { get; set; }

    public string InputMetadata { get; set; }

    [Required]
    public string OutputMetadata { get; set; }

    [Output]
    public ITaskItem[] OutputItems { get; set; }

    public override bool Execute()
    {
        OutputItems = Items;

        foreach (var item in Items)
        {
            var value = string.IsNullOrEmpty(InputMetadata) ? item.ItemSpec : item.GetMetadata(InputMetadata);
            if (string.IsNullOrEmpty(value))
            {
                continue;
            }

            byte[] fullHash;
            using (var sha2 = SHA256.Create())
            {
                fullHash = sha2.ComputeHash(Encoding.UTF8.GetBytes(value));
            }

            int targetBlockSize = Marshal.SizeOf(typeof(Guid));

            // SHA256 will produce a 32 byte hash, but GUIDs are only 16 bytes in size, so we simply partition the hash array into
            // two 16 byte arrays (via Take and Skip) and then Zip them together into a resultant 16 byte array by XORing the 
            // corresponding byte from each array and storing the result.
            byte[] reducedHash = fullHash.Take(targetBlockSize).Zip(fullHash.Skip(targetBlockSize), (b1, b2) => (byte)(b1 ^ b2)).ToArray();
            Debug.Assert(reducedHash.Length == targetBlockSize);

            item.SetMetadata(OutputMetadata, new Guid(reducedHash).ToString("B").ToUpperInvariant());
        }

        return !Log.HasLoggedErrors;
    }
}