using System.Net.Http.Headers;
using System.Security.Cryptography;
using System.Text;
using System.Text.Json;
using Fitness_core_BE.DTOs.PaymentGateways;
using Fitness_core_BE.Exceptions;
using Fitness_core_BE.Infra.UoW;
using Fitness_core_BE.Interfaces;
using Fitness_core_BE.Interfaces.Services;

namespace Fitness_core_BE.Services
{
    public class PaymentGatewayClient : IPaymentGatewayClient
    {
        private readonly IClientRepository _clientRepository;
        private readonly IPaymentServiceClient _paymentServiceClient;
        private readonly IUnitOfWork _uow;
        private readonly HttpClient _httpClient;
        private readonly string _baseUrl;
        private static readonly JsonSerializerOptions JsonOptions = new() { PropertyNameCaseInsensitive = true };

        public PaymentGatewayClient(
            IClientRepository clientRepository,
            IPaymentServiceClient paymentServiceClient,
            IUnitOfWork uow,
            IHttpClientFactory httpClientFactory,
            IConfiguration configuration)
        {
            _clientRepository = clientRepository;
            _paymentServiceClient = paymentServiceClient;
            _uow = uow;
            _httpClient = httpClientFactory.CreateClient();
            _baseUrl = (configuration["PaymentService:BaseUrl"] ?? "http://127.0.0.1:5120").TrimEnd('/');
        }

        public async Task<OnboardCardResult> OnboardCardAsync(Guid clientId, OnboardCardRequest request, CancellationToken ct = default)
        {
            var body = await SendAsync(clientId, HttpMethod.Post, "/api/v1/cards/onboard", request, ct);
            return Deserialize<OnboardCardResult>(body);
        }

        public async Task<CardDetailsResult> GetCardDetailsAsync(Guid clientId, string cardToken, CancellationToken ct = default)
        {
            var body = await SendAsync(clientId, HttpMethod.Get, $"/api/v1/cards/{Uri.EscapeDataString(cardToken)}", null, ct);
            return Deserialize<CardDetailsResult>(body);
        }

        public async Task<IReadOnlyCollection<CardDetailsResult>> ListCardsAsync(Guid clientId, string customerId, CancellationToken ct = default)
        {
            var body = await SendAsync(clientId, HttpMethod.Get, "/api/v1/cards", null, ct,
                query: $"customerId={Uri.EscapeDataString(customerId)}");
            return Deserialize<List<CardDetailsResult>>(body);
        }

        public async Task DeactivateCardAsync(Guid clientId, string cardToken, CancellationToken ct = default)
        {
            await SendAsync(clientId, HttpMethod.Delete, $"/api/v1/cards/{Uri.EscapeDataString(cardToken)}", null, ct);
        }

        public async Task<SetDefaultCardResult> SetDefaultCardAsync(Guid clientId, string cardToken, string customerId, CancellationToken ct = default)
        {
            var body = await SendAsync(clientId, HttpMethod.Patch, $"/api/v1/cards/{Uri.EscapeDataString(cardToken)}/default",
                new { customerId }, ct);
            return Deserialize<SetDefaultCardResult>(body);
        }

        public async Task<OnboardCardResult> GetOnboardingStatusAsync(Guid clientId, string gatewayName, string sessionId, CancellationToken ct = default)
        {
            var body = await SendAsync(clientId, HttpMethod.Get,
                $"/api/v1/cards/onboarding/{Uri.EscapeDataString(gatewayName)}/{Uri.EscapeDataString(sessionId)}", null, ct);
            return Deserialize<OnboardCardResult>(body);
        }

        public async Task<AttemptPaymentResult> AttemptPaymentAsync(Guid clientId, AttemptPaymentRequest request, CancellationToken ct = default)
        {
            var body = await SendAsync(clientId, HttpMethod.Post, "/api/v1/payments/attempt", request, ct);
            return Deserialize<AttemptPaymentResult>(body);
        }

        public async Task<RefundPaymentResult> RefundPaymentAsync(Guid clientId, Guid paymentId, bool isVoid, CancellationToken ct = default)
        {
            var body = await SendAsync(clientId, HttpMethod.Post, $"/api/v1/refunds/{paymentId}", new { isVoid }, ct);
            return Deserialize<RefundPaymentResult>(body);
        }

        public async Task<PaymentListResult> ListPaymentsAsync(Guid clientId, string? cardToken, int page, int pageSize, CancellationToken ct = default)
        {
            var queryParts = new List<string> { $"page={page}", $"pageSize={pageSize}" };
            if (!string.IsNullOrWhiteSpace(cardToken))
            {
                queryParts.Add($"cardToken={Uri.EscapeDataString(cardToken)}");
            }

            var body = await SendAsync(clientId, HttpMethod.Get, "/api/v1/payments", null, ct, query: string.Join("&", queryParts));
            return Deserialize<PaymentListResult>(body);
        }

        private static T Deserialize<T>(string body)
        {
            return JsonSerializer.Deserialize<T>(body, JsonOptions)
                ?? throw new ServiceUnavailableException("Payment-Service returned an empty response.");
        }

        /// <summary>
        /// Mints this client's Payment-Service Platform the first time it's needed, storing the
        /// ApiKey/HmacSecret on Client since Payment-Service only ever returns them once.
        /// </summary>
        private async Task<(string ApiKey, string HmacSecret)> EnsureCredentialsAsync(Guid clientId, CancellationToken ct)
        {
            var client = await _clientRepository.GetClientEntityByIdAsync(clientId, ct)
                ?? throw new NotFoundException($"Client {clientId} not found.");

            if (string.IsNullOrEmpty(client.ClientPaymentApiKey) || string.IsNullOrEmpty(client.ClientPaymentHmacSecret))
            {
                var (platformId, apiKey, hmacSecret) = await _paymentServiceClient.ProvisionPlatformAsync(
                    clientId, client.ClientName ?? "Gym", ct);

                client.FKPaymentPlatformId = platformId;
                client.ClientPaymentApiKey = apiKey;
                client.ClientPaymentHmacSecret = hmacSecret;
                await _uow.SaveChangesAsync(ct);
            }

            return (client.ClientPaymentApiKey!, client.ClientPaymentHmacSecret!);
        }

        private async Task<string> SendAsync(Guid clientId, HttpMethod method, string path, object? body, CancellationToken ct, string? query = null)
        {
            var (apiKey, hmacSecret) = await EnsureCredentialsAsync(clientId, ct);

            var bodyJson = body is null ? string.Empty : JsonSerializer.Serialize(body);
            var timestamp = DateTimeOffset.UtcNow.ToString("o");
            // Signed over the path only — Payment-Service's HmacValidationMiddleware signs
            // against Request.Path.Value, which never includes the query string.
            var signature = ComputeSignature(hmacSecret, method.Method, path, timestamp, bodyJson);

            var url = string.IsNullOrEmpty(query) ? $"{_baseUrl}{path}" : $"{_baseUrl}{path}?{query}";
            using var httpRequest = new HttpRequestMessage(method, url);
            httpRequest.Headers.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
            httpRequest.Headers.Add("X-Api-Key", apiKey);
            httpRequest.Headers.Add("X-Timestamp", timestamp);
            httpRequest.Headers.Add("X-Signature", signature);

            if (body is not null)
            {
                httpRequest.Content = new StringContent(bodyJson, Encoding.UTF8, "application/json");
            }

            HttpResponseMessage response;
            try
            {
                response = await _httpClient.SendAsync(httpRequest, ct);
            }
            catch (HttpRequestException ex)
            {
                throw new ServiceUnavailableException("Could not reach Payment-Service.", ex);
            }

            var responseBody = await response.Content.ReadAsStringAsync(ct);
            if (!response.IsSuccessStatusCode)
            {
                throw new ServiceUnavailableException($"Payment-Service call failed ({(int)response.StatusCode}): {responseBody}");
            }

            return responseBody;
        }

        // Must match Payment-Service's Middleware/HmacValidationMiddleware.ComputeSignature
        // exactly: METHOD\nPATH\nTIMESTAMP\nBODY, HMACSHA256, hex lowercase.
        private static string ComputeSignature(string secret, string method, string path, string timestamp, string body)
        {
            using var hmac = new HMACSHA256(Encoding.UTF8.GetBytes(secret));
            var payload = $"{method}\n{path}\n{timestamp}\n{body}";
            var hash = hmac.ComputeHash(Encoding.UTF8.GetBytes(payload));
            return Convert.ToHexString(hash).ToLowerInvariant();
        }
    }
}