feat: implement CreateMessageBatchAsync method

src/AnthropicClient/AnthropicApiClient.cs

@@ -28,6 +28,13 @@ public interface IAnthropicApiClient
   /// <returns>An asynchronous enumerable that yields the response event by event.</returns>
   IAsyncEnumerable<AnthropicEvent> CreateMessageAsync(StreamMessageRequest request);
 
+  /// <summary>
+  /// Creates a batch of messages asynchronously.
+  /// </summary>
+  /// <param name="request">The message batch request to create.</param>
+  /// <returns>A task that represents the asynchronous operation. The task result contains the response as an <see cref="AnthropicResult{T}"/> where T is <see cref="MessageBatchResponse"/>.</returns>
+  Task<AnthropicResult<MessageBatchResponse>> CreateMessageBatchAsync(MessageBatchRequest request);
+
   /// <summary>
   /// Counts the tokens in a message asynchronously.
   /// </summary>
@@ -64,7 +71,8 @@ public class AnthropicApiClient : IAnthropicApiClient
   private const string BaseUrl = "https://api.anthropic.com/v1/";
   private const string ApiKeyHeader = "x-api-key";
   private const string MessagesEndpoint = "messages";
-  private const string CountTokensEndpoint = "messages/count_tokens";
+  private string CountTokensEndpoint => $"{MessagesEndpoint}/count-tokens";
+  private string MessageBatchesEndpoint => $"{MessagesEndpoint}/batches";
   private const string ModelsEndpoint = "models";
   private const string JsonContentType = "application/json";
   private const string EventPrefix = "event:";
@@ -287,6 +295,23 @@ public class AnthropicApiClient : IAnthropicApiClient
     } while (true);
   }
 
+  /// <inheritdoc/>
+  public async Task<AnthropicResult<MessageBatchResponse>> CreateMessageBatchAsync(MessageBatchRequest request)
+  {
+    var response = await SendRequestAsync(MessageBatchesEndpoint, request);
+    var anthropicHeaders = new AnthropicHeaders(response.Headers);
+    var responseContent = await response.Content.ReadAsStringAsync();
+
+    if (response.IsSuccessStatusCode is false)
+    {
+      var error = Deserialize<AnthropicError>(responseContent) ?? new AnthropicError();
+      return AnthropicResult<MessageBatchResponse>.Failure(error, anthropicHeaders);
+    }
+
+    var msgBatchResponse = Deserialize<MessageBatchResponse>(responseContent) ?? new MessageBatchResponse();
+    return AnthropicResult<MessageBatchResponse>.Success(msgBatchResponse, anthropicHeaders);
+  }
+
   /// <inheritdoc/>
   public async Task<AnthropicResult<TokenCountResponse>> CountMessageTokensAsync(CountMessageTokensRequest request)
   {

src/AnthropicClient/Models/MessageBatchRequest.cs

@@ -0,0 +1,28 @@
+namespace AnthropicClient.Models;
+
+/// <summary>
+/// Represents a request to create a batch of messages.
+/// </summary>
+public class MessageBatchRequest
+{
+  /// <summary>
+  /// Gets the requests to create messages.
+  /// </summary>
+  public List<MessageBatchRequestItem> Requests { get; init; } = [];
+
+  /// <summary>
+  /// Initializes a new instance of the <see cref="MessageBatchRequest"/> class.
+  /// </summary>
+  /// <param name="requests">The requests to create messages.</param>
+  /// <exception cref="ArgumentException">Thrown when <paramref name="requests"/> is empty.</exception>
+  /// <returns>An instance of the <see cref="MessageBatchRequest"/> class.</returns>
+  public MessageBatchRequest(List<MessageBatchRequestItem> requests)
+  {
+    if (requests.Count == 0)
+    {
+      throw new ArgumentException($"{nameof(requests)} must not be empty.", nameof(requests));
+    }
+
+    Requests = requests;
+  }
+}

src/AnthropicClient/Models/MessageBatchRequestItem.cs

@@ -0,0 +1,39 @@
+using System.Text.Json.Serialization;
+
+using AnthropicClient.Utils;
+
+namespace AnthropicClient.Models;
+
+/// <summary>
+/// Represents an item in a batch of messages.
+/// </summary>
+public class MessageBatchRequestItem
+{
+  /// <summary>
+  /// Gets the custom identifier for the message.
+  /// </summary>
+  [JsonPropertyName("custom_id")]
+  public string CustomId { get; init; }
+
+  /// <summary>
+  /// Gets the message request parameters.
+  /// </summary>
+  public MessageRequest Params { get; init; }
+
+  /// <summary>
+  /// Initializes a new instance of the <see cref="MessageBatchRequestItem"/> class.
+  /// </summary>
+  /// <param name="customId">The custom identifier for the message.</param>
+  /// <param name="messageRequest">The message request parameters.</param>
+  /// <exception cref="ArgumentException">Thrown when <paramref name="customId"/> is null or whitespace.</exception>
+  /// <exception cref="ArgumentException">Thrown when <paramref name="messageRequest"/> is null.</exception>
+  /// <returns>An instance of the <see cref="MessageBatchRequestItem"/> class.</returns>
+  public MessageBatchRequestItem(string customId, MessageRequest messageRequest)
+  {
+    ArgumentValidator.ThrowIfNullOrWhitespace(customId, nameof(customId));
+    ArgumentValidator.ThrowIfNull(messageRequest, nameof(messageRequest));
+
+    CustomId = customId;
+    Params = messageRequest;
+  }
+}

src/AnthropicClient/Models/MessageBatchResponse.cs

@@ -0,0 +1,98 @@
+using System.Text.Json.Serialization;
+
+namespace AnthropicClient.Models;
+
+/// <summary>
+/// Represents a response to a batch of messages.
+/// </summary>
+public class MessageBatchResponse
+{
+  /// <summary>
+  /// Gets the identifier of the batch.
+  /// </summary>
+  public string Id { get; init; } = string.Empty;
+
+  /// <summary>
+  /// Gets the type of the batch.
+  /// </summary>
+  public string Type { get; init; } = string.Empty;
+
+  /// <summary>
+  /// Gets the processing status of the batch.
+  /// </summary>
+  [JsonPropertyName("processing_status")]
+  public string ProcessingStatus { get; init; } = string.Empty;
+
+  /// <summary>
+  /// Gets the counts of requests in the batch.
+  /// </summary>
+  [JsonPropertyName("request_counts")]
+  public MessageBatchRequestCounts RequestCounts { get; init; } = new MessageBatchRequestCounts();
+
+  /// <summary>
+  /// Gets the date and time when the batch ended.
+  /// </summary>
+  [JsonPropertyName("ended_at")]
+  public DateTimeOffset EndedAt { get; init; }
+
+  /// <summary>
+  /// Gets the date and time when the batch was created.
+  /// </summary>
+  [JsonPropertyName("created_at")]
+  public DateTimeOffset CreatedAt { get; init; }
+
+  /// <summary>
+  /// Gets the date and time when the batch expires.
+  /// </summary>
+  [JsonPropertyName("expires_at")]
+  public DateTimeOffset ExpiresAt { get; init; }
+
+  /// <summary>
+  /// Gets the date and time when the batch was archived.
+  /// </summary>
+  [JsonPropertyName("archived_at")]
+  public DateTimeOffset ArchivedAt { get; init; }
+
+  /// <summary>
+  /// Gets the date and time when the batch cancellation was initiated.
+  /// </summary>
+  [JsonPropertyName("cancel_initiated_at")]
+  public DateTimeOffset CancelInitiatedAt { get; init; }
+
+  /// <summary>
+  /// Gets the URL to the results of the batch.
+  /// </summary>
+  [JsonPropertyName("results_url")]
+  public string ResultsUrl { get; init; } = string.Empty;
+}
+
+/// <summary>
+/// Represents the counts of requests in a batch of messages.
+/// </summary>
+public class MessageBatchRequestCounts
+{
+  /// <summary>
+  /// Gets the number of requests in the batch that are processing.
+  /// </summary>
+  public int Processing { get; init; }
+
+  /// <summary>
+  /// Gets the number of requests in the batch that succeeded.
+  /// </summary>
+  public int Succeeded { get; init; }
+
+  /// <summary>
+  /// Gets the number of requests in the batch that errored.
+  /// </summary>
+  public int Errored { get; init; }
+
+  /// <summary>
+  /// Gets the number of requests in the batch that were cancelled.
+  /// </summary>
+  public int Canceled { get; init; }
+
+  /// <summary>
+  /// Gets the number of requests in the batch that expired.
+  /// </summary>
+  public int Expired { get; init; }
+}