LMEMappeCatastaliProApp/Services/OfficialCadastreService.cs

using System.Globalization;
using System.Net;
using System.Net.Http.Headers;
using System.Xml.Linq;

namespace LMEMappeCatastaliApp.Services;

public sealed class OfficialCadastreService
{
    private const string WfsEndpoint = "https://wfs.cartografia.agenziaentrate.gov.it/inspire/wfs/owfs01.php";
    private readonly HttpClient _httpClient = new()
    {
        Timeout = TimeSpan.FromSeconds(30)
    };

    public OfficialCadastreService()
    {
        _httpClient.DefaultRequestHeaders.UserAgent.ParseAdd("LMEMappeCatastali/1.0 (Android)");
        _httpClient.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/gml+xml"));
        _httpClient.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/xml", 0.9));
    }

    public async Task<string> GetParcelsNearAsync(
        double latitude,
        double longitude,
        double radiusMeters,
        CancellationToken cancellationToken = default)
    {
        var firstRadius = Math.Clamp(radiusMeters, 12, 30);
        var xml = await GetFeaturesNearAsync(
            latitude,
            longitude,
            firstRadius,
            "CP:CadastralParcel",
            100,
            cancellationToken);

        if (firstRadius >= 30 || ContainsFeatures(xml))
        {
            return xml;
        }

        return await GetFeaturesNearAsync(
            latitude,
            longitude,
            30,
            "CP:CadastralParcel",
            100,
            cancellationToken);
    }

    public async Task<string> GetSheetsNearAsync(
        double latitude,
        double longitude,
        double radiusMeters = 10,
        CancellationToken cancellationToken = default)
        => await GetFeaturesNearAsync(
            latitude,
            longitude,
            radiusMeters,
            "CP:CadastralZoning",
            20,
            cancellationToken);

    private async Task<string> GetFeaturesNearAsync(
        double latitude,
        double longitude,
        double radiusMeters,
        string typeName,
        int count,
        CancellationToken cancellationToken)
    {
        var meters = Math.Clamp(radiusMeters, 2, 30);
        var deltaLatitude = meters / 111_320d;
        var longitudeScale = Math.Cos(latitude * Math.PI / 180d);
        var deltaLongitude = meters / (111_320d * Math.Max(0.1, longitudeScale));
        var bbox = string.Join(",",
        [
            Format(latitude - deltaLatitude),
            Format(longitude - deltaLongitude),
            Format(latitude + deltaLatitude),
            Format(longitude + deltaLongitude)
        ]);

        var query = new Dictionary<string, string>
        {
            ["language"] = "ita",
            ["SERVICE"] = "WFS",
            ["VERSION"] = "2.0.0",
            ["TYPENAMES"] = typeName,
            ["SRSNAME"] = "urn:ogc:def:crs:EPSG::6706",
            ["BBOX"] = bbox,
            ["REQUEST"] = "GetFeature",
            ["COUNT"] = count.ToString(CultureInfo.InvariantCulture)
        };

        var url = WfsEndpoint + "?" + string.Join("&", query.Select(item =>
            $"{Uri.EscapeDataString(item.Key)}={Uri.EscapeDataString(item.Value)}"));

        for (var attempt = 0; attempt < 3; attempt++)
        {
            try
            {
                using var request = new HttpRequestMessage(HttpMethod.Get, url)
                {
                    Version = HttpVersion.Version11,
                    VersionPolicy = HttpVersionPolicy.RequestVersionOrLower
                };
                request.Headers.CacheControl = new CacheControlHeaderValue { NoCache = true };

                using var response = await _httpClient.SendAsync(
                    request,
                    HttpCompletionOption.ResponseContentRead,
                    cancellationToken);
                if (response.IsSuccessStatusCode)
                {
                    var xml = await response.Content.ReadAsStringAsync(cancellationToken);
                    ThrowIfExceptionReport(xml);
                    return xml;
                }

                if (attempt < 2 && IsTransient(response.StatusCode))
                {
                    await Task.Delay(TimeSpan.FromMilliseconds(500 * (attempt + 1)), cancellationToken);
                    continue;
                }

                throw new HttpRequestException($"Il servizio WFS AdE ha risposto {((int)response.StatusCode)}.");
            }
            catch (HttpRequestException) when (attempt < 2)
            {
                await Task.Delay(TimeSpan.FromMilliseconds(500 * (attempt + 1)), cancellationToken);
            }
            catch (TaskCanceledException) when (!cancellationToken.IsCancellationRequested && attempt < 2)
            {
                await Task.Delay(TimeSpan.FromMilliseconds(500 * (attempt + 1)), cancellationToken);
            }
        }

        throw new HttpRequestException("Il servizio WFS AdE non ha risposto dopo tre tentativi.");
    }

    private static bool IsTransient(HttpStatusCode statusCode) =>
        statusCode is HttpStatusCode.RequestTimeout or HttpStatusCode.TooManyRequests
        || (int)statusCode >= 500;

    private static bool ContainsFeatures(string xml)
    {
        try
        {
            var document = XDocument.Parse(xml);
            return document.Descendants().Any(element =>
                element.Name.LocalName is "member" or "featureMember");
        }
        catch (System.Xml.XmlException)
        {
            return false;
        }
    }

    private static string Format(double value) => value.ToString("R", CultureInfo.InvariantCulture);

    private static void ThrowIfExceptionReport(string xml)
    {
        try
        {
            var document = XDocument.Parse(xml);
            var exceptionText = document.Descendants()
                .FirstOrDefault(element => element.Name.LocalName == "ExceptionText")
                ?.Value
                .Trim();
            if (!string.IsNullOrWhiteSpace(exceptionText))
            {
                throw new InvalidOperationException($"Servizio WFS AdE: {exceptionText}");
            }
        }
        catch (System.Xml.XmlException error)
        {
            throw new InvalidDataException("Il servizio WFS AdE ha restituito una risposta non valida.", error);
        }
    }
}