using System;
using System.Security.Cryptography;
using System.Text;
using Microsoft.AspNetCore.DataProtection;

namespace isnd.Helpers
{
    public static class ApiKeyProtector
    {
        private const byte LegacyDelta = 145;

        public static string TryUnprotectKey(IDataProtector protector, string protectedValue)
        {
            if (string.IsNullOrWhiteSpace(protectedValue))
            {
                return protectedValue;
            }

            if (TryUnprotect(protector, protectedValue, out var unprotected))
            {
                return unprotected;
            }

            if (TryUnprotectLegacy(protectedValue, out unprotected))
            {
                return unprotected;
            }

            return protectedValue;
        }

        private static bool TryUnprotect(IDataProtector protector, string protectedValue, out string unprotected)
        {
            try
            {
                unprotected = protector.Unprotect(protectedValue);
                return true;
            }
            catch (CryptographicException)
            {
                unprotected = null;
                return false;
            }
            catch (FormatException)
            {
                unprotected = null;
                return false;
            }
        }

        private static bool TryUnprotectLegacy(string protectedValue, out string unprotected)
        {
            try
            {
                unprotected = UnprotectLegacy(protectedValue);
                return true;
            }
            catch (FormatException)
            {
                unprotected = null;
                return false;
            }
        }

        public static string UnprotectLegacy(string protectedValue)
        {
            if (string.IsNullOrWhiteSpace(protectedValue))
            {
                return protectedValue;
            }

            var bytes = Convert.FromBase64String(protectedValue);
            var unprotectedBytes = new byte[bytes.Length];
            for (var index = 0; index < bytes.Length; index++)
            {
                unprotectedBytes[index] = (byte)(bytes[index] ^ LegacyDelta);
            }

            return Encoding.UTF8.GetString(unprotectedBytes);
        }
    }
}