using System.Text;
using System.Text.Json;
using Application.Abstractions.Crypto;
using Application.Abstractions.Data;
using Application.Abstractions.Payment;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Logging;

namespace Infrastructure.Payment;

/// <summary>
/// 토스페이먼츠 V2 API 클라이언트.
/// - 인증: Basic base64(secretKey + ":") — 콜론 1개 필수, Encoding.UTF8.GetBytes 는 BOM 미포함.
/// - POST 에 Idempotency-Key(UUID v4) 부여 — 동일 키 재요청 시 첫 응답 반환(중복 승인 방지).
/// - 통신 불명 예외(HttpRequestException/TaskCanceledException)는 전파 — 호출측이 NeedsReconciliation 분기. (Phase 1.5)
/// - 명시적 거절(HTTP 4xx/5xx + {code, message} 본문)은 Success=false 로 반환.
/// </summary>
internal sealed class TossPaymentService(
    HttpClient httpClient,
    IAppDbContext db,
    IFieldEncryptor encryptor,
    ILogger<TossPaymentService> logger
) : ITossPaymentService
{
    private const string BaseUrl = "https://api.tosspayments.com";

    public async Task<TossClientConfig> GetClientConfigAsync(CancellationToken ct)
    {
        var (clientKey, _) = await GetKeysAsync(ct);
        return new TossClientConfig(clientKey);
    }

    public async Task<TossPaymentResult> ConfirmAsync(string paymentKey, string orderID, int amount, CancellationToken ct)
    {
        var (_, secretKey) = await GetKeysAsync(ct);

        var request = new HttpRequestMessage(HttpMethod.Post, $"{BaseUrl}/v1/payments/confirm");
        request.Headers.Add("Authorization", BuildBasicAuth(secretKey));
        request.Headers.Add("Idempotency-Key", Guid.NewGuid().ToString());

        var body = new
        {
            paymentKey,
            orderId = orderID,
            amount
        };

        request.Content = new StringContent(JsonSerializer.Serialize(body), Encoding.UTF8, "application/json");

        var response = await httpClient.SendAsync(request, ct);
        var json = await response.Content.ReadAsStringAsync(ct);

        logger.LogInformation("[TossPay] Confirm response: {StatusCode} {Body}", response.StatusCode, json);

        return Parse(response.IsSuccessStatusCode, json);
    }

    public async Task<TossPaymentResult> CancelAsync(string paymentKey, string cancelReason, int? cancelAmount, CancellationToken ct)
    {
        var (_, secretKey) = await GetKeysAsync(ct);

        var request = new HttpRequestMessage(HttpMethod.Post, $"{BaseUrl}/v1/payments/{Uri.EscapeDataString(paymentKey)}/cancel");
        request.Headers.Add("Authorization", BuildBasicAuth(secretKey));
        request.Headers.Add("Idempotency-Key", Guid.NewGuid().ToString());

        // cancelAmount 미지정 = 전액 취소 (필드 자체를 보내지 않는다)
        var json = cancelAmount is null
            ? JsonSerializer.Serialize(new { cancelReason })
            : JsonSerializer.Serialize(new { cancelReason, cancelAmount });

        request.Content = new StringContent(json, Encoding.UTF8, "application/json");

        var response = await httpClient.SendAsync(request, ct);
        var responseJson = await response.Content.ReadAsStringAsync(ct);

        logger.LogInformation("[TossPay] Cancel response: {StatusCode} {Body}", response.StatusCode, responseJson);

        return Parse(response.IsSuccessStatusCode, responseJson);
    }

    public async Task<TossPaymentResult> GetPaymentAsync(string paymentKey, CancellationToken ct)
    {
        var (_, secretKey) = await GetKeysAsync(ct);

        // GET 은 Idempotency-Key 미적용 (무시됨)
        var request = new HttpRequestMessage(HttpMethod.Get, $"{BaseUrl}/v1/payments/{Uri.EscapeDataString(paymentKey)}");
        request.Headers.Add("Authorization", BuildBasicAuth(secretKey));

        var response = await httpClient.SendAsync(request, ct);
        var json = await response.Content.ReadAsStringAsync(ct);

        logger.LogInformation("[TossPay] GetPayment response: {StatusCode} paymentKey={PaymentKey}", response.StatusCode, paymentKey);

        return Parse(response.IsSuccessStatusCode, json);
    }

    // ── Private ──────────────────────────────────────────────────────

    private static TossPaymentResult Parse(bool httpSuccess, string json)
    {
        JsonElement doc;
        try
        {
            doc = JsonSerializer.Deserialize<JsonElement>(json);
        }
        catch (JsonException ex)
        {
            // 게이트웨이 HTML 오류 등 비정상 본문 — 실패 단정 금지, 통신 불명으로 전파해 대사 대상으로 처리
            throw new HttpRequestException($"토스 응답 본문 파싱 실패: {ex.Message}", ex);
        }

        string? Get(JsonElement el, string key) => el.ValueKind == JsonValueKind.Object && el.TryGetProperty(key, out var p) && p.ValueKind == JsonValueKind.String ? p.GetString() : null;
        int? GetInt(JsonElement el, string key) => el.ValueKind == JsonValueKind.Object && el.TryGetProperty(key, out var p) && p.ValueKind == JsonValueKind.Number ? p.GetInt32() : null;
        DateTime? GetDate(JsonElement el, string key)
        {
            var raw = Get(el, key);
            return DateTimeOffset.TryParse(raw, out var parsed) ? parsed.UtcDateTime : null;
        }

        if (!httpSuccess)
        {
            // 에러 응답 {code, message}
            return new TossPaymentResult(
                false,
                Get(doc, "code") ?? "UNKNOWN",
                Get(doc, "message") ?? "결제 요청에 실패했습니다.",
                Get(doc, "paymentKey"), Get(doc, "orderId"), null, null, null, null, null,
                null, null, null, null, [], json
            );
        }

        // 영수증
        string? receiptUrl = null;
        if (doc.TryGetProperty("receipt", out var receipt))
        {
            receiptUrl = Get(receipt, "url");
        }

        // 가상계좌
        string? vaNumber = null;
        string? vaBankCode = null;
        string? vaHolder = null;
        DateTime? vaDueDate = null;
        if (doc.TryGetProperty("virtualAccount", out var va) && va.ValueKind == JsonValueKind.Object)
        {
            vaNumber = Get(va, "accountNumber");
            vaBankCode = Get(va, "bankCode") ?? Get(va, "bank");
            vaHolder = Get(va, "customerName");
            vaDueDate = GetDate(va, "dueDate");
        }

        // 취소 이력
        var cancels = new List<TossCancelDetail>();
        if (doc.TryGetProperty("cancels", out var cancelArray) && cancelArray.ValueKind == JsonValueKind.Array)
        {
            foreach (var c in cancelArray.EnumerateArray())
            {
                cancels.Add(new TossCancelDetail(Get(c, "transactionKey"), GetInt(c, "cancelAmount") ?? 0, Get(c, "cancelReason"), GetDate(c, "canceledAt")));
            }
        }

        return new TossPaymentResult(
            true, null, null,
            Get(doc, "paymentKey"),
            Get(doc, "orderId"),
            Get(doc, "status"),
            GetInt(doc, "totalAmount"),
            Get(doc, "method"),
            GetDate(doc, "approvedAt"),
            receiptUrl,
            vaNumber, vaBankCode, vaHolder, vaDueDate,
            cancels, json
        );
    }

    private async Task<(string ClientKey, string SecretKey)> GetKeysAsync(CancellationToken ct)
    {
        var config = await db.Config.FirstOrDefaultAsync(ct);
        if (config?.External is null)
        {
            throw new InvalidOperationException("토스페이먼츠 결제 설정이 없습니다. 관리자 페이지에서 설정해주세요.");
        }

        var ext = config.External;
        var isLive = string.Equals(ext.TossPayMode, "live", StringComparison.OrdinalIgnoreCase);

        var clientKey = isLive ? ext.TossLiveClientKeyEnc : ext.TossTestClientKeyEnc;
        var secretKey = isLive ? ext.TossLiveSecretKeyEnc : ext.TossTestSecretKeyEnc;

        if (string.IsNullOrEmpty(clientKey) || string.IsNullOrEmpty(secretKey))
        {
            throw new InvalidOperationException($"토스페이먼츠 {(isLive ? "라이브" : "테스트")} 설정이 불완전합니다.");
        }

        // Admin 결제 설정 화면이 "enc:v{n}:" 포맷으로 암호화 저장 — 레거시 평문은 그대로 통과
        return (EncryptedConfigValue.Unprotect(encryptor, clientKey), EncryptedConfigValue.Unprotect(encryptor, secretKey));
    }

    private static string BuildBasicAuth(string secretKey)
    {
        // SecretKey + ":" → Base64 (콜론 1개 필수, BOM 없이 인코딩)
        var raw = $"{secretKey}:";
        var base64 = Convert.ToBase64String(Encoding.UTF8.GetBytes(raw));
        return $"Basic {base64}";
    }
}