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

namespace Centron.Api.docuFORM.Helper
{
    public static class OAuthHelper
    {
        // Can be used to generate a "state" or the codeVerifier for the "code challenge"
        public static string GenerateRandomBase64String(int byteLength = 32)
        {
            byte[] randomBytes = new byte[byteLength];
            using (var rng = RandomNumberGenerator.Create())
            {
                rng.GetBytes(randomBytes);
            }
            
            // Base64 URL-safe encoding
            string state = Convert.ToBase64String(randomBytes)
                .Replace("+", "-")
                .Replace("/", "_")
                .Replace("=", "");
            
            return state;
        }

        public static string GenerateCodeChallenge(string codeVerifier)
        {
            using (var sha256 = SHA256.Create())
            {
                byte[] hash = sha256.ComputeHash(Encoding.ASCII.GetBytes(codeVerifier));
                string codeChallenge = Convert.ToBase64String(hash)
                    .Replace("+", "-")
                    .Replace("/", "_")
                    .Replace("=", "");
                return codeChallenge;
            }
        }
    }
}