using System;
using System.Text;
using System.Security.Cryptography;

namespace xIds.Helpers
{
    /// <summary>
    /// Api Key Generating Helper Class ...
    /// </summary>
    public static class XApiKeyHelper
    {
        /// <summary>
        /// Compute Hash of Specified Content using SHA256 ...
        /// </summary>
        /// <param name="plain"></param>
        /// <returns></returns>
        public static string ComputeHash(string plain)
        {
            //
            using var sha256 = SHA256.Create();
            var hashBytes = sha256.ComputeHash(Encoding.UTF8.GetBytes(plain));
            var result = BitConverter.ToString(hashBytes)
                .Replace("-", "")
                .ToLower();

            //
            return result;
        }

        /// <summary>
        /// Generate an Api Key ...
        /// </summary>
        /// <returns></returns>
        public static (string plainKey, string hash, string prefix) Generate(string keyPrefix)
        {
            //
            // Generate 32 bytes of cryptographically secure random data
            var randomBytes = new byte[32];
            using (var rng = RandomNumberGenerator.Create())
            {
                rng.GetBytes(randomBytes);
            }

            //
            // Format: xapp_{base64url}
            var plainKey = $"{keyPrefix}_{Convert.ToBase64String(randomBytes)
                .Replace("+", "-").Replace("/", "_").TrimEnd('=')}";

            //
            // Compute Hash ...
            var hash = ComputeHash(plainKey);

            //
            // Prefix for quick identification (first 12 chars)
            var prefix = plainKey.Substring(0, 16) + "...";

            //
            return (plainKey, hash, prefix);
        }

        /// <summary>
        /// Verify Generating Api Key ...
        /// </summary>
        /// <param name="plainKey"></param>
        /// <param name="storedHash"></param>
        /// <returns></returns>
        public static bool Verify(
            string plainKey,
            string storedHash
        )
        {
            //
            var hash = ComputeHash(plainKey);
            return hash == storedHash;
        }
    }
}