using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Security.Cryptography;
using System.Text;
using System.Threading.Tasks;

namespace BS.Shared.Core
{
	public static class SecurityUtils
	{
		private static readonly char[] InvalidFilenameChars = Path.GetInvalidFileNameChars();

		public static bool ContainsInvalidFilenameChars(string fileName)
		{
			return fileName.IndexOfAny(InvalidFilenameChars) >= 0;
		}

		public static string SanitizeFilename(string fileName)
		{
			if (String.IsNullOrEmpty(fileName) || !ContainsInvalidFilenameChars(fileName))
			{
				return fileName;
			}

			var sb = new StringBuilder(fileName.Length);
			foreach (char c in fileName)
			{
				if (!InvalidFilenameChars.Contains(c))
				{
					sb.Append(c);
				}
			}
			return sb.ToString();
		}

		public static string GetChecksum(string filePath)
		{
			using (FileStream stream = File.OpenRead(filePath))
			{
				var sha = new SHA256Managed();
				byte[] checksum = sha.ComputeHash(stream);
				return BitConverter.ToString(checksum).Replace("-", String.Empty);
			}
		}

		public static string GetChecksumBuffered(Stream stream)
		{
			using (var bufferedStream = new BufferedStream(stream, 1024 * 32))
			{
				var sha = new SHA256Managed();
				byte[] checksum = sha.ComputeHash(bufferedStream);
				return BitConverter.ToString(checksum).Replace("-", String.Empty);
			}
		}
	}
}