using Microsoft.IdentityModel.Tokens;
using System.IdentityModel.Tokens.Jwt;
using System.Security.Claims;
using System.Text;

namespace Fitness_core_BE.Helpers
{
    // Mints/validates the short-lived token for the public "pay by link" page used for
    // platform (HexaFitness -> gym) invoices. Parallel to InvoicePaymentTokenHelper
    // (which is scoped to member-level CustomerInvoice) rather than a shared/generalized
    // helper, to avoid touching the token shape already relied on by live member links.
    public class PlatformInvoicePaymentTokenHelper
    {
        private readonly string _signingKey;
        private readonly int _expiresInDays;

        public PlatformInvoicePaymentTokenHelper(IConfiguration configuration)
        {
            _signingKey = configuration["InvoicePaymentToken:SigningKey"]
                ?? throw new InvalidOperationException("InvoicePaymentToken:SigningKey is not configured.");
            _expiresInDays = int.TryParse(configuration["InvoicePaymentToken:ExpiresInDays"], out var d) ? d : 7;
        }

        public string Generate(Guid clientInvoiceId)
        {
            var key = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(_signingKey));
            var creds = new SigningCredentials(key, SecurityAlgorithms.HmacSha256);

            var claims = new[]
            {
                new Claim("ClientInvoiceId", clientInvoiceId.ToString()),
                new Claim("Purpose", "PlatformInvoicePayment")
            };

            var expires = DateTime.UtcNow.AddDays(_expiresInDays);
            var token = new JwtSecurityToken(claims: claims, expires: expires, signingCredentials: creds);

            return new JwtSecurityTokenHandler().WriteToken(token);
        }

        public Guid? ValidateAndGetInvoiceId(string token)
        {
            var key = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(_signingKey));
            var handler = new JwtSecurityTokenHandler();

            try
            {
                var principal = handler.ValidateToken(token, new TokenValidationParameters
                {
                    ValidateIssuer = false,
                    ValidateAudience = false,
                    ValidateLifetime = true,
                    ValidateIssuerSigningKey = true,
                    IssuerSigningKey = key,
                    ClockSkew = TimeSpan.FromMinutes(2)
                }, out _);

                if (principal.FindFirst("Purpose")?.Value != "PlatformInvoicePayment")
                    return null;

                var idClaim = principal.FindFirst("ClientInvoiceId")?.Value;
                return Guid.TryParse(idClaim, out var id) ? id : null;
            }
            catch
            {
                return null;
            }
        }
    }
}