using System;
using System.Globalization;
using System.Runtime.CompilerServices;
using System.Security.Cryptography;
using System.Text;

namespace MileageTraker.Web.Membership
{
	public static class Crypto
	{
		private const int TokenSizeInBytes = 16;
		private const int Pbkdf2Count = 1000;
		private const int Pbkdf2SubkeyLength = 256/8;
		private const int SaltSize = 128/8;


		public static string GenerateSalt(int byteLength = SaltSize)
		{
			var Buff = new byte[byteLength];
			using (var Prng = new RNGCryptoServiceProvider())
			{
				Prng.GetBytes(Buff);
			}

			return Convert.ToBase64String(Buff);
		}

		public static string Hash(string input, string algorithm = "sha256")
		{
			if (input == null)
			{
				throw new ArgumentNullException("input");
			}

			return Hash(Encoding.UTF8.GetBytes(input), algorithm);
		}

		public static string Hash(byte[] input, string algorithm = "sha256")
		{
			if (input == null)
			{
				throw new ArgumentNullException("input");
			}

			using (HashAlgorithm alg = HashAlgorithm.Create(algorithm))
			{
				if (alg != null)
				{
					byte[] hashData = alg.ComputeHash(input);
					return BinaryToHex(hashData);
				}
				else
				{
					throw new InvalidOperationException(String.Format(CultureInfo.InvariantCulture, "not supported hash alg", algorithm));
				}
			}
		}

		public static string SHA1(string input)
		{
			return Hash(input, "sha1");
		}

		public static string SHA256(string input)
		{
			return Hash(input, "sha256");
		}

		/* =======================
         * HASHED PASSWORD FORMATS
         * =======================
         * 
         * Version 0:
         * PBKDF2 with HMAC-SHA1, 128-bit salt, 256-bit subkey, 1000 iterations.
         * (See also: SDL crypto guidelines v5.1, Part III)
         * Format: { 0x00, salt, subkey }
         */

		public static string HashPassword(string password)
		{
			if (password == null)
			{
				throw new ArgumentNullException("password");
			}

			byte[] salt;
			byte[] subkey;
			using (var deriveBytes = new Rfc2898DeriveBytes(password, SaltSize, Pbkdf2Count))
			{
				salt = deriveBytes.Salt;
				subkey = deriveBytes.GetBytes(Pbkdf2SubkeyLength);
			}

			var outputBytes = new byte[1 + SaltSize + Pbkdf2SubkeyLength];
			Buffer.BlockCopy(salt, 0, outputBytes, 1, SaltSize);
			Buffer.BlockCopy(subkey, 0, outputBytes, 1 + SaltSize, Pbkdf2SubkeyLength);
			return Convert.ToBase64String(outputBytes);
		}

		// hashedPassword must be of the format of HashWithPassword (salt + Hash(salt+input)
		public static bool VerifyHashedPassword(string hashedPassword, string password)
		{
			if (hashedPassword == null)
			{
				throw new ArgumentNullException("hashedPassword");
			}
			if (password == null)
			{
				throw new ArgumentNullException("password");
			}

			byte[] hashedPasswordBytes = Convert.FromBase64String(hashedPassword);

			// Verify a version 0 (see comment above) password hash.

			if (hashedPasswordBytes.Length != (1 + SaltSize + Pbkdf2SubkeyLength) || hashedPasswordBytes[0] != 0x00)
			{
				// Wrong length or version header.
				return false;
			}

			var salt = new byte[SaltSize];
			Buffer.BlockCopy(hashedPasswordBytes, 1, salt, 0, SaltSize);
			var storedSubkey = new byte[Pbkdf2SubkeyLength];
			Buffer.BlockCopy(hashedPasswordBytes, 1 + SaltSize, storedSubkey, 0, Pbkdf2SubkeyLength);

			byte[] generatedSubkey;
			using (var deriveBytes = new Rfc2898DeriveBytes(password, salt, Pbkdf2Count))
			{
				generatedSubkey = deriveBytes.GetBytes(Pbkdf2SubkeyLength);
			}
			return ByteArraysEqual(storedSubkey, generatedSubkey);
		}

		internal static string BinaryToHex(byte[] data)
		{
			var hex = new char[data.Length*2];

			for (int iter = 0; iter < data.Length; iter++)
			{
				var hexChar = ((byte) (data[iter] >> 4));
				hex[iter*2] = (char) (hexChar > 9 ? hexChar + 0x37 : hexChar + 0x30);
				hexChar = ((byte) (data[iter] & 0xF));
				hex[iter*2 + 1] = (char) (hexChar > 9 ? hexChar + 0x37 : hexChar + 0x30);
			}
			return new string(hex);
		}

		// Compares two byte arrays for equality. The method is specifically written so that the loop is not optimized.
		[MethodImpl(MethodImplOptions.NoOptimization)]
		private static bool ByteArraysEqual(byte[] a, byte[] b)
		{
			if (ReferenceEquals(a, b))
			{
				return true;
			}

			if (a == null || b == null || a.Length != b.Length)
			{
				return false;
			}

			bool areSame = true;
			for (int i = 0; i < a.Length; i++)
			{
				areSame &= (a[i] == b[i]);
			}
			return areSame;
		}
	}
}