Improve cadastral GPS reliability and mobile overlays

Services/OfficialCadastreService.cs

@@ -1,4 +1,6 @@
 using System.Globalization;
+using System.Net;
+using System.Net.Http.Headers;
 using System.Xml.Linq;
 
 namespace LMEMappeCatastaliApp.Services;
@@ -13,8 +15,9 @@ public sealed class OfficialCadastreService
 
     public OfficialCadastreService()
     {
-        _httpClient.DefaultRequestHeaders.UserAgent.ParseAdd("LMEMappeCatastali/0.2");
-        _httpClient.DefaultRequestHeaders.Accept.ParseAdd("application/gml+xml");
+        _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(
@@ -22,14 +25,30 @@ public sealed class OfficialCadastreService
         double longitude,
         double radiusMeters,
         CancellationToken cancellationToken = default)
-        => await GetFeaturesNearAsync(
+    {
+        var firstRadius = Math.Clamp(radiusMeters, 12, 30);
+        var xml = await GetFeaturesNearAsync(
             latitude,
             longitude,
-            radiusMeters,
+            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,
@@ -78,15 +97,65 @@ public sealed class OfficialCadastreService
         var url = WfsEndpoint + "?" + string.Join("&", query.Select(item =>
             $"{Uri.EscapeDataString(item.Key)}={Uri.EscapeDataString(item.Value)}"));
 
-        using var response = await _httpClient.GetAsync(url, HttpCompletionOption.ResponseContentRead, cancellationToken);
-        if (!response.IsSuccessStatusCode)
+        for (var attempt = 0; attempt < 3; attempt++)
         {
-            throw new HttpRequestException($"Il servizio WFS AdE ha risposto {((int)response.StatusCode)}.");
+            try
+            {
+                using var request = new HttpRequestMessage(HttpMethod.Get, url)
+                {
+                    Version = HttpVersion.Version11,
+                    VersionPolicy = HttpVersionPolicy.RequestVersionOrLower
+                };
+                request.Headers.CacheControl = new CacheControlHeaderValue { NoCache = true };
+
+                using var response = await _httpClient.SendAsync(
+                    request,
+                    HttpCompletionOption.ResponseContentRead,
+                    cancellationToken);
+                if (response.IsSuccessStatusCode)
+                {
+                    var xml = await response.Content.ReadAsStringAsync(cancellationToken);
+                    ThrowIfExceptionReport(xml);
+                    return xml;
+                }
+
+                if (attempt < 2 && IsTransient(response.StatusCode))
+                {
+                    await Task.Delay(TimeSpan.FromMilliseconds(500 * (attempt + 1)), cancellationToken);
+                    continue;
+                }
+
+                throw new HttpRequestException($"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);
+            }
         }
 
-        var xml = await response.Content.ReadAsStringAsync(cancellationToken);
-        ThrowIfExceptionReport(xml);
-        return xml;
+        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);