using StackExchange.Redis;
using System.Text.Json;
using System.Security.Cryptography;
using System.Text;

namespace GB5Shared.OTP
{
    public class EmailOtpRedisService
    {
        private readonly IDatabase _db;
        private const int ExpiryMinutes = 5;
        private const int MaxAttempts = 5;

        public EmailOtpRedisService(IConnectionMultiplexer redis)
        {
            _db = redis.GetDatabase();
        }

        private static string NormalizeEmail(string email)
            => email.Trim().ToLower();

        private static string HashOtp(string otp)
        {
            using var sha = SHA256.Create();
            var bytes = sha.ComputeHash(Encoding.UTF8.GetBytes(otp));
            return Convert.ToBase64String(bytes);
        }

        public async Task SaveOtpAsync(string email, string otp, string ConnectionName)
        {
            email = NormalizeEmail(email);

            var key = $"OTP:EMAIL{ConnectionName}:{email}";
            var hashedOtp = HashOtp(otp);

            var value = JsonSerializer.Serialize(new OtpData
            {
                OtpHash = hashedOtp,
                Attempts = 0
            });

            await _db.StringSetAsync(
                key,
                value,
                TimeSpan.FromMinutes(ExpiryMinutes)
            );
        }

        public async Task<bool> VerifyOtpAsync(string email, string inputOtp,string ConnectionName)
        {
            email = NormalizeEmail(email);
            var key = $"OTP:EMAIL{ConnectionName}:{email}";

            var value = await _db.StringGetAsync(key);
            if (value.IsNullOrEmpty)
                return false;

            var ttl = await _db.KeyTimeToLiveAsync(key);
            if (ttl == null)
                return false;

            var data = JsonSerializer.Deserialize<OtpData>((string)value!)!;

            if (data.Attempts >= MaxAttempts)
                return false;

            if (data.OtpHash != HashOtp(inputOtp))
            {
                data.Attempts++;

                await _db.StringSetAsync(
                    key,
                    JsonSerializer.Serialize(data),
                    ttl
                );

                return false;
            }

            // OTP SUCCESS → DELETE
            await _db.KeyDeleteAsync(key);
            return true;
        }

        private class OtpData
        {
            public string OtpHash { get; set; } = "";
            public int Attempts { get; set; }
        }
    }
}