using FileShare_Common.Core;
using FileShare_Services.Core;
using Microsoft.Extensions.Configuration;
using QRCoder;
using System.Net;
using System.Net.NetworkInformation;
using System.Net.Sockets;

namespace FileShare_Services.Services.QrCode
{
    /// <summary>
    /// 二维码生成服务，获取局域网 IP 并生成 PNG 格式的访问二维码。
    /// </summary>
    public sealed class QrCodeService(IConfiguration configuration) : IQrCodeService
    {
        /// <inheritdoc />
        public Task<object?> GenerateQrCodeAsync(ServiceEndpointContext ctx)
        {
            var ip = GetLanIpAddress();
            if (ip is null)
                throw new InvalidOperationException("无法获取局域网IP地址");

            var port = int.TryParse(configuration["Server:HttpPort"], out var p) ? p : 5206;
            var url = $"http://{ip}:{port}";
            var base64 = GeneratePngBase64(url);
            return Task.FromResult<object?>(ResponseHelper.Ok(new QrCodeResponse(url, base64)));
        }

        /// <summary>
        /// 使用 QRCoder 库生成指定内容的二维码，输出为 Base64 编码的 PNG data URI。
        /// </summary>
        /// <param name="content">二维码编码内容。</param>
        /// <returns>data URI 格式的 Base64 PNG 字符串。</returns>
        private static string GeneratePngBase64(string content)
        {
            using var generator = new QRCodeGenerator();
            using var data = generator.CreateQrCode(content, QRCodeGenerator.ECCLevel.Q);
            using var png = new PngByteQRCode(data);
            var bytes = png.GetGraphic(20);
            return $"data:image/png;base64,{Convert.ToBase64String(bytes)}";
        }

        /// <summary>
        /// 获取本机第一个可用的局域网 IPv4 地址，排除回环地址和 APIPA 地址（169.254.x.x）。
        /// </summary>
        /// <returns>局域网 IP 地址字符串，无可用地址时返回 null。</returns>
        private static string? GetLanIpAddress()
        {
            return NetworkInterface.GetAllNetworkInterfaces()
                .Where(ni => ni.OperationalStatus == OperationalStatus.Up
                             && ni.NetworkInterfaceType != NetworkInterfaceType.Loopback)
                .SelectMany(ni => ni.GetIPProperties().UnicastAddresses)
                .Select(ua => ua.Address)
                .FirstOrDefault(ip =>
                    ip.AddressFamily == AddressFamily.InterNetwork
                    && !IPAddress.IsLoopback(ip)
                    && !ip.ToString().StartsWith("169.254"))
                ?.ToString();
        }
    }
}