Add EnvelopeDto and EnvelopeService for API integration

Introduced the `EnvelopeDto` class to represent envelope data with JSON property mappings. Added the `EnvelopeService` class to handle API interactions, including fetching envelopes with optional filters and query string construction using `Microsoft.AspNetCore.WebUtilities`. Updated the project file to include the required package reference for query string manipulation.

EnvelopeGenerator.ReceiverUI/EnvelopeGenerator.ReceiverUI.csproj

@@ -29,6 +29,7 @@
     <PackageReference Include="DevExpress.Blazor.Reporting.Viewer" Version="25.2.3" />
     <PackageReference Include="DevExpress.Drawing.Skia" Version="25.2.3" />
     <PackageReference Include="HarfBuzzSharp.NativeAssets.WebAssembly" Version="8.3.1.2" />
+    <PackageReference Include="Microsoft.AspNetCore.WebUtilities" Version="8.0.28" />
     <PackageReference Include="SkiaSharp.NativeAssets.WebAssembly" Version="3.119.1" />
     <PackageReference Include="SkiaSharp.Views.Blazor" Version="3.119.1" />
     <NativeFileReference Include="$(HarfBuzzSharpStaticLibraryPath)\2.0.23\*.a" />

EnvelopeGenerator.ReceiverUI/Models/EnvelopeDto.cs

@@ -0,0 +1,24 @@
+using System.Text.Json.Serialization;
+
+namespace EnvelopeGenerator.ReceiverUI.Models;
+
+public class EnvelopeDto
+{
+    [JsonPropertyName("id")]
+    public int Id { get; set; }
+
+    [JsonPropertyName("uuid")]
+    public string? Uuid { get; set; }
+
+    [JsonPropertyName("title")]
+    public string? Title { get; set; }
+
+    [JsonPropertyName("status")]
+    public int Status { get; set; }
+
+    [JsonPropertyName("docResult")]
+    public byte[]? DocResult { get; set; }
+
+    [JsonPropertyName("envelopeReceivers")]
+    public List<EnvelopeReceiverDto> EnvelopeReceivers { get; set; } = new();
+}

EnvelopeGenerator.ReceiverUI/Services/EnvelopeService.cs

@@ -0,0 +1,72 @@
+using System.Net.Http.Json;
+using System.Text.Json;
+using EnvelopeGenerator.ReceiverUI.Models;
+using EnvelopeGenerator.ReceiverUI.Options;
+using Microsoft.AspNetCore.WebUtilities;
+using Microsoft.Extensions.Options;
+
+namespace EnvelopeGenerator.ReceiverUI.Services;
+
+/// <summary>
+/// Retrieves <see cref="EnvelopeDto"/>s from the API.
+/// </summary>
+public class EnvelopeService
+{
+    private readonly HttpClient _http;
+    private readonly ApiOptions _apiOptions;
+    private static readonly JsonSerializerOptions _jsonOptions = new(JsonSerializerDefaults.Web);
+
+    public EnvelopeService(HttpClient http, IOptions<ApiOptions> apiOptions)
+    {
+        _http = http;
+        _apiOptions = apiOptions.Value;
+    }
+
+    /// <summary>
+    /// Fetches envelopes from the API with optional filters.
+    /// </summary>
+    /// <exception cref="HttpRequestException">Thrown when the API request fails.</exception>
+    public async Task<IEnumerable<EnvelopeDto>?> GetAsync(
+        int? id = null,
+        string? uuid = null,
+        bool? onlyActive = null,
+        bool? onlyCompleted = null,
+        CancellationToken cancel = default)
+    {
+        var baseUrl = $"{_apiOptions.BaseUrl}/api/Envelope";
+        var queryParams = new Dictionary<string, string?>();
+
+        if (id.HasValue)
+        {
+            queryParams["Id"] = id.Value.ToString();
+        }
+        if (!string.IsNullOrEmpty(uuid))
+        {
+            queryParams["Uuid"] = uuid;
+        }
+        if (onlyActive.HasValue)
+        {
+            queryParams["OnlyActive"] = onlyActive.Value.ToString();
+        }
+        if (onlyCompleted.HasValue)
+        {
+            queryParams["OnlyCompleted"] = onlyCompleted.Value.ToString();
+        }
+
+        var url = QueryHelpers.AddQueryString(baseUrl, queryParams);
+
+        var response = await _http.GetAsync(url, cancel);
+
+        if (!response.IsSuccessStatusCode)
+        {
+            var statusCode = (int)response.StatusCode;
+            var reasonPhrase = response.ReasonPhrase ?? "Unknown error";
+            throw new HttpRequestException(
+                $"Failed to load envelopes. Status: {statusCode} ({reasonPhrase})",
+                null,
+                response.StatusCode);
+        }
+
+        return await response.Content.ReadFromJsonAsync<IEnumerable<EnvelopeDto>>(_jsonOptions, cancel);
+    }
+}