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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
#nullable disable
using System.Numerics;
using System.Security.Cryptography;
using Microsoft.Build.Framework;
using Microsoft.Build.Utilities;
namespace Microsoft.AspNetCore.StaticWebAssets.Tasks;
public class ComputeCssScope : Task
{
[Required]
public ITaskItem[] ScopedCssInput { get; set; }
[Required]
public string TargetName { get; set; }
[Output]
public ITaskItem[] ScopedCss { get; set; }
public override bool Execute()
{
ScopedCss = new ITaskItem[ScopedCssInput.Length];
for (var i = 0; i < ScopedCssInput.Length; i++)
{
var input = ScopedCssInput[i];
var relativePath = input.ItemSpec.ToLowerInvariant().Replace("\\", "//");
var scope = input.GetMetadata("CssScope");
scope = !string.IsNullOrEmpty(scope) ? scope : GenerateScope(TargetName, relativePath);
var outputItem = new TaskItem(input);
outputItem.SetMetadata("CssScope", scope);
ScopedCss[i] = outputItem;
}
return !Log.HasLoggedErrors;
}
private static string GenerateScope(string targetName, string relativePath)
{
var bytes = Encoding.UTF8.GetBytes(relativePath + targetName);
#if !NET9_0_OR_GREATER
using var sha256 = SHA256.Create();
var hashBytes = sha256.ComputeHash(bytes);
#else
var hashBytes = SHA256.HashData(bytes);
#endif
var builder = new StringBuilder();
builder.Append("b-");
builder.Append(ToBase36(hashBytes));
return builder.ToString();
}
private static string ToBase36(byte[] hash)
{
const string chars = "0123456789abcdefghijklmnopqrstuvwxyz";
var result = new char[10];
#if NET9_0_OR_GREATER
var dividend = BigInteger.Abs(new BigInteger([.. hash.AsSpan()[..9]]));
#else
var dividend = BigInteger.Abs(new BigInteger([.. hash.AsSpan(0, 9)]));
#endif
for (var i = 0; i < 10; i++)
{
dividend = BigInteger.DivRem(dividend, 36, out var remainder);
result[i] = chars[(int)remainder];
}
return new string(result);
}
}
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