using System.IO.Enumeration;
using System.Security.Cryptography;

if (args.Length < 2)
{
    Console.WriteLine("Usage: HashSumJ <algo> <dir-tree-to-checksum> [parallel:default same to vCpu]");
    Console.WriteLine("   algo: MD5 SHA256 SHA512 SHA1");
    return -1;
}

Func<string, string> hashAlgo = args[0].ToLower() switch
{
    "md5" => MakeMd5FromFilePath,
    "sha256" => MakeSha256FromFilePath,
    "sha512" => MakeSha512FromFilePath,
    "sha1" => MakeSha1FromFilePath,
    _ => throw new ArgumentException("algo")
};

var dirToCheckSum = args[1];

var threads = Environment.ProcessorCount;
if (args.Length > 1 && ushort.TryParse(args[1], out var t)) threads = t;

var files = new FileSystemEnumerable<string>(dirToCheckSum, (ref FileSystemEntry p) => p.ToFullPath(),
        new EnumerationOptions { RecurseSubdirectories = true, })
{ ShouldIncludePredicate = (ref FileSystemEntry p) => p.IsDirectory == false };

var arrFilesPath = files.ToArray();

var num = 0;

Parallel.ForEach(arrFilesPath,
    new ParallelOptions { MaxDegreeOfParallelism = threads },
    f =>
    {
        try
        {
            Console.WriteLine($"{hashAlgo(f)}|{f}|t#{Environment.CurrentManagedThreadId}|{Interlocked.Increment(ref num)} of {arrFilesPath.Length}");
        }
        catch (Exception e)
        {
            Console.WriteLine($"Err: {e.Message}");
        }
    });

return 0;

static string MakeMd5FromFilePath(string filePath)
{
    using var fs = File.OpenRead(filePath);
    return Convert.ToHexString(MD5.HashData(fs));
}

static string MakeSha1FromFilePath(string filePath)
{
    using var fs = File.OpenRead(filePath);
    return Convert.ToHexString(SHA1.HashData(fs));
}

static string MakeSha256FromFilePath(string filePath)
{
    using var fs = File.OpenRead(filePath);
    return Convert.ToHexString(SHA256.HashData(fs));
}

static string MakeSha512FromFilePath(string filePath)
{
    using var fs = File.OpenRead(filePath);
    return Convert.ToHexString(SHA512.HashData(fs));
}