using System;
using System.Collections.Generic;
using System.Security.Cryptography;
using System.Text;

namespace Sarand.Net.Standard.Base.Data
{
	//=======================================================================
	public static class SacsShaHasher
	{
		//-------------------------------------------------------------------
		// Properties.
		public static String ShaSaltDelim { get; } = ":";
		public static String Sha256Prefix { get; } = "Sha256:";
		public static String Sha384Prefix { get; } = "Sha384:";
		public static String Sha512Prefix { get; } = "Sha512:";

		//-------------------------------------------------------------------
		// Ref. https://xamarinhelp.com/cryptography-in-xamarin-forms/
		// Hash Salt.
		// To add a salt to the hash, append the Salt (random string) to the value.
		// The Salt can be stored with the hashed value.
		// Salts do not need to be kept secret and should be different for each hash.
		// This is to reduce the impact of pre-built hash tables, eg. where common passwords (‘password’) generate the same Hash.
		// It also stops the same password generating the identical Hash for 2 different accounts.
		//-------------------------------------------------------------------
		/// <summary>
		/// Non-reversible encryption.
		/// <para>Result is converted to Base64 string to ensure that all bytes are properly recorded, as UTF8 doesn’t have an exact byte match for each possible byte sequence.</para>
		/// <para>Algorythm must be dispoed by calling routine.</para>
		/// </summary>
		public static string HashString (this string value, HashAlgorithm algorythm)
		{
			return Convert.ToBase64String(algorythm.ComputeHash(System.Text.Encoding.UTF8.GetBytes(value)));
		}

		//-------------------------------------------------------------------
		/// <summary>
		/// Non-reversible encryption using Sha256.
		/// <para>Result is converted to Base64 string to ensure that all bytes are properly recorded, as UTF8 doesn’t have an exact byte match for each possible byte sequence.</para>
		/// </summary>
		public static string HashSha256 (this string value)
		{
			using (HashAlgorithm algorythm = SHA256.Create())
			{
				return HashString(value, algorythm);
			}
		}

		//-------------------------------------------------------------------
		/// <summary>
		/// Non-reversible encryption using Sha384.
		/// <para>Result is converted to Base64 string to ensure that all bytes are properly recorded, as UTF8 doesn’t have an exact byte match for each possible byte sequence.</para>
		/// </summary>
		public static string HashSha384 (this string value)
		{
			using (HashAlgorithm algorythm = SHA384.Create())
			{
				return HashString(value, algorythm);
			}
		}

		//-------------------------------------------------------------------
		/// <summary>
		/// Non-reversible encryption using Sha512.
		/// <para>Result is converted to Base64 string to ensure that all bytes are properly recorded, as UTF8 doesn’t have an exact byte match for each possible byte sequence.</para>
		/// </summary>
		public static string HashSha512 (this string value)
		{
			using (HashAlgorithm algorythm = SHA512.Create())
			{
				return HashString(value, algorythm);
			}
		}

		//-------------------------------------------------------------------
	}
	//=======================================================================
}