using System.Security.Cryptography;
using System.Text;
using Fake.Application;
using Fake.DependencyInjection;
using Microsoft.AspNetCore.Http;
using Oms.Domain.CustomersAggregate.Entities;
using Oms.Domain.CustomersAggregate.Enums;
using Oms.Domain.CustomersAggregate.Repositories;

namespace Oms.Application.Shared;

/// <summary>
/// 客户 OpenAPI 机机鉴权：appKey + timestamp + HMAC-SHA256(sign)，Secret 仅本地参与签名。
/// </summary>
public class CustomerOpenApiAuthHelper : IScopedDependency
{
    public const string AppKeyHeaderName = "appKey";
    public const string TimestampHeaderName = "timestamp";
    public const string SignHeaderName = "sign";

    /// <summary>签名时间窗（秒）。</summary>
    public const int TimestampSkewSeconds = 300;

    private readonly ICustomerOpenApiCredentialRepository _credentialRepository;
    private readonly ICustomerRepository _customerRepository;
    private readonly IHttpContextAccessor _httpContextAccessor;

    public CustomerOpenApiAuthHelper(
        ICustomerOpenApiCredentialRepository credentialRepository,
        ICustomerRepository customerRepository,
        IHttpContextAccessor httpContextAccessor)
    {
        _credentialRepository = credentialRepository;
        _customerRepository = customerRepository;
        _httpContextAccessor = httpContextAccessor;
    }

    /// <summary>
    /// 校验 Header 签名并解析主客户。
    /// stringToSign = appKey + "\n" + timestamp + "\n" + sha256Hex(rawBody)
    /// sign = hex(HMAC-SHA256(appSecret, stringToSign))
    /// </summary>
    public async Task<(Customer Customer, CustomerOpenApiCredential Credential)> ResolveSignedAsync(
        string? appKey,
        string? timestamp,
        string? sign,
        string? rawBody,
        CancellationToken cancellationToken = default)
    {
        var key = appKey?.Trim();
        var tsRaw = timestamp?.Trim();
        var signRaw = sign?.Trim();
        if (string.IsNullOrWhiteSpace(key)
            || string.IsNullOrWhiteSpace(tsRaw)
            || string.IsNullOrWhiteSpace(signRaw))
        {
            throw new BusinessException("凭证无效");
        }

        if (!long.TryParse(tsRaw, out var unixSeconds))
        {
            throw new BusinessException("请求已过期");
        }

        var now = DateTimeOffset.UtcNow.ToUnixTimeSeconds();
        if (Math.Abs(now - unixSeconds) > TimestampSkewSeconds)
        {
            throw new BusinessException("请求已过期");
        }

        var credential = await _credentialRepository.GetByAppKeyAsync(key, cancellationToken);
        if (credential == null
            || !credential.Enabled
            || string.IsNullOrWhiteSpace(credential.AppSecret))
        {
            throw new BusinessException("凭证无效");
        }

        var expectedSign = ComputeSign(key, tsRaw, rawBody ?? string.Empty, credential.AppSecret);
        if (!FixedTimeEqualsUtf8(expectedSign, signRaw.ToLowerInvariant()))
        {
            throw new BusinessException("签名无效");
        }

        var customer = await _customerRepository.FirstOrDefaultAsync(
            x => x.Id == credential.CustomerId,
            cancellationToken);
        if (customer == null
            || customer.ParentCustomerId.HasValue
            || customer.Status != CustomerStatus.Normal)
        {
            throw new BusinessException("凭证无效");
        }

        credential.LastUsedAt = DateTime.Now;
        credential.LastUsedIp = ResolveClientIp();
        await _credentialRepository.UpdateAsync(credential);

        return (customer, credential);
    }

    /// <summary>
    /// 客户端可复用：计算 sign（小写 hex）。
    /// </summary>
    public static string ComputeSign(string appKey, string timestamp, string rawBody, string appSecret)
    {
        var bodyHash = Sha256Hex(rawBody ?? string.Empty);
        var stringToSign = $"{appKey}\n{timestamp}\n{bodyHash}";
        return HmacSha256Hex(appSecret, stringToSign);
    }

    private static string Sha256Hex(string text)
    {
        var bytes = SHA256.HashData(Encoding.UTF8.GetBytes(text));
        return Convert.ToHexString(bytes).ToLowerInvariant();
    }

    private static string HmacSha256Hex(string secret, string content)
    {
        var keyBytes = Encoding.UTF8.GetBytes(secret);
        var contentBytes = Encoding.UTF8.GetBytes(content);
        var hash = HMACSHA256.HashData(keyBytes, contentBytes);
        return Convert.ToHexString(hash).ToLowerInvariant();
    }

    private static bool FixedTimeEqualsUtf8(string? expected, string actual)
    {
        if (string.IsNullOrEmpty(expected))
        {
            return false;
        }

        var left = Encoding.UTF8.GetBytes(expected);
        var right = Encoding.UTF8.GetBytes(actual);
        return left.Length == right.Length
            && CryptographicOperations.FixedTimeEquals(left, right);
    }

    private string? ResolveClientIp()
    {
        var http = _httpContextAccessor.HttpContext;
        if (http == null)
        {
            return null;
        }

        var forwarded = http.Request.Headers["X-Forwarded-For"].FirstOrDefault();
        if (!string.IsNullOrWhiteSpace(forwarded))
        {
            return forwarded.Split(',')[0].Trim();
        }

        return http.Connection.RemoteIpAddress?.ToString();
    }
}