feat(ReadDocumentQueryHandler): Logik hinzugefügt

EnvelopeGenerator.Application/Documents/Queries/Read/ReadDocumentQueryHandler.cs

@@ -1,19 +1,48 @@
-using EnvelopeGenerator.Application.Contracts.Repositories;
+using DigitalData.Core.Abstractions.Infrastructure;
+using EnvelopeGenerator.Application.Contracts.Repositories;
+using EnvelopeGenerator.Domain.Entities;
 using MediatR;
 
 namespace EnvelopeGenerator.Application.Documents.Queries.Read;
 
-public class ReadDocumentQueryHandler : IRequestHandler<ReadDocumentQuery, ReadDocumentResponse>
+/// <summary>
+/// Handles queries for reading <see cref="EnvelopeDocument"/> data based on either the document ID or the envelope ID.
+/// </summary>
+public class ReadDocumentQueryHandler : IRequestHandler<ReadDocumentQuery, ReadDocumentResponse?>
 {
-    public IEnvelopeDocumentRepository _repo;
+    /// <summary>
+    /// Repository for accessing <see cref="EnvelopeDocument"/> entities.
+    /// </summary>
+    private readonly IRepository<EnvelopeDocument> _repo;
 
-    public ReadDocumentQueryHandler(IEnvelopeDocumentRepository envelopeDocumentRepository)
+    /// <summary>
+    /// Initializes a new instance of the <see cref="ReadDocumentQueryHandler"/> class.
+    /// </summary>
+    /// <param name="envelopeDocumentRepository">The repository used to access <see cref="EnvelopeDocument"/> entities.</param>
+    public ReadDocumentQueryHandler(IRepository<EnvelopeDocument> envelopeDocumentRepository)
     {
         _repo = envelopeDocumentRepository;
     }
 
-    public Task<ReadDocumentResponse> Handle(ReadDocumentQuery query, CancellationToken cancellationToken)
+    /// <summary>
+    /// Handles the <see cref="ReadDocumentQuery"/> and returns a <see cref="ReadDocumentResponse"/> based on the provided identifiers.
+    /// </summary>
+    /// <param name="query">The query containing the document ID or envelope ID to search for.</param>
+    /// <param name="cancellationToken">A token to monitor for cancellation requests.</param>
+    /// <returns>
+    /// A <see cref="ReadDocumentResponse"/> if a matching document is found; otherwise, <c>null</c>.
+    /// </returns>
+    /// <exception cref="InvalidOperationException">
+    /// Thrown when neither <see cref="ReadDocumentQuery.Id"/> nor <see cref="ReadDocumentQuery.EnvelopeId"/> is provided.
+    /// </exception>
+    public async Task<ReadDocumentResponse?> Handle(ReadDocumentQuery query, CancellationToken cancellationToken)
     {
-        throw new NotImplementedException();
+        if (query.Id is not null)
+            return await _repo.ReadOrDefaultAsync<ReadDocumentResponse>(d => d.Id == query.Id);
+        else if (query.EnvelopeId is not null)
+            return await _repo.ReadOrDefaultAsync<ReadDocumentResponse>(d => d.EnvelopeId == query.EnvelopeId);
+
+        throw new InvalidOperationException(
+            $"Invalid {nameof(ReadDocumentQuery)}: either {nameof(query.Id)} or {nameof(query.EnvelopeId)} must be provided.");
     }
 }