using System;
using System.IO;
using System.Text;
using System.Reflection;
using System.Runtime.CompilerServices;
using System.Security.Cryptography;

public static class HashAlgorithm<THashAlgorithm>
    where THashAlgorithm : HashAlgorithm
{
    /// <summary>
    /// 线程静态变量：即该变量在每个线程中唯一目的是为了避开多线程问题
    /// </summary>
    [ThreadStatic]
    private static THashAlgorithm instance;

    /// <summary>
    /// 哈希算法单例。
    /// </summary>
    public static THashAlgorithm Instance => instance ?? Create();

    public static string ComputeHash(Stream input)
    {
        var instance = Instance;

        var bytes = instance.ComputeHash(input);

        var result = Convert.ToBase64String(bytes);

        return result;
    }

    public static string ComputeHash(byte[] input)
    {
        var instance = Instance;

        var bytes = instance.ComputeHash(input);

        var result = Convert.ToBase64String(bytes);

        return result;
    }

    public static string ComputeHash(string input)
    {
        var bytes = Encoding.UTF8.GetBytes(input);
        
        return ComputeHash(bytes);
    }

    [MethodImpl(MethodImplOptions.NoInlining)]
    private static THashAlgorithm Create()
    {
        var createMethod = typeof(THashAlgorithm).GetMethod(
            nameof(HashAlgorithm.Create),
            BindingFlags.Public | BindingFlags.Static | BindingFlags.DeclaredOnly,
            Type.DefaultBinder,
            Type.EmptyTypes,
            null);

        if (createMethod != null)
            instance = (THashAlgorithm)createMethod.Invoke(null, new object[] { });
        else
            instance = Activator.CreateInstance<THashAlgorithm>();

        return instance;
    }
}