Fix Mistral AI Chat model function call usage calculation

 - Fix the chat model's call() to calculate the cumulative usage
   - Use an explicit internalCall to pass the previous chat response so that accumulation can be done

 - Fix the chat model's stream() to calculate the cumulative usage
   - Fix MistralAi API to include usgae in ChatCompletionChunk
   - Use internalStream() to accumulate the usage

Add/update tests

Author: ilayaperumalg

models/spring-ai-mistral-ai/src/main/java/org/springframework/ai/mistralai/MistralAiChatModel.java

@@ -36,6 +36,8 @@
 import org.springframework.ai.chat.messages.UserMessage;
 import org.springframework.ai.chat.metadata.ChatGenerationMetadata;
 import org.springframework.ai.chat.metadata.ChatResponseMetadata;
+import org.springframework.ai.chat.metadata.Usage;
+import org.springframework.ai.chat.metadata.UsageUtils;
 import org.springframework.ai.chat.model.AbstractToolCallSupport;
 import org.springframework.ai.chat.model.ChatModel;
 import org.springframework.ai.chat.model.ChatResponse;
@@ -74,6 +76,7 @@
  * @author Grogdunn
  * @author Thomas Vitale
  * @author luocongqiu
+ * @author Ilayaperumal Gopinathan
  * @since 1.0.0
  */
 public class MistralAiChatModel extends AbstractToolCallSupport implements ChatModel {
@@ -155,8 +158,22 @@ public static ChatResponseMetadata from(MistralAiApi.ChatCompletion result) {
 			.build();
 	}
 
+	public static ChatResponseMetadata from(MistralAiApi.ChatCompletion result, Usage usage) {
+		Assert.notNull(result, "Mistral AI ChatCompletion must not be null");
+		return ChatResponseMetadata.builder()
+			.withId(result.id())
+			.withModel(result.model())
+			.withUsage(usage)
+			.withKeyValue("created", result.created())
+			.build();
+	}
+
 	@Override
 	public ChatResponse call(Prompt prompt) {
+		return this.internalCall(prompt, null);
+	}
+
+	public ChatResponse internalCall(Prompt prompt, ChatResponse previousChatResponse) {
 
 		MistralAiApi.ChatCompletionRequest request = createRequest(prompt, false);
 
@@ -192,7 +209,10 @@ public ChatResponse call(Prompt prompt) {
 					return buildGeneration(choice, metadata);
 				}).toList();
 
-				ChatResponse chatResponse = new ChatResponse(generations, from(completionEntity.getBody()));
+				MistralAiUsage usage = MistralAiUsage.from(completionEntity.getBody().usage());
+				Usage cumulativeUsage = UsageUtils.getCumulativeUsage(usage, previousChatResponse);
+				ChatResponse chatResponse = new ChatResponse(generations,
+						from(completionEntity.getBody(), cumulativeUsage));
 
 				observationContext.setResponse(chatResponse);
 
@@ -205,14 +225,18 @@ && isToolCall(response, Set.of(MistralAiApi.ChatCompletionFinishReason.TOOL_CALL
 			var toolCallConversation = handleToolCalls(prompt, response);
 			// Recursively call the call method with the tool call message
 			// conversation that contains the call responses.
-			return this.call(new Prompt(toolCallConversation, prompt.getOptions()));
+			return this.internalCall(new Prompt(toolCallConversation, prompt.getOptions()), response);
 		}
 
 		return response;
 	}
 
 	@Override
 	public Flux<ChatResponse> stream(Prompt prompt) {
+		return this.internalStream(prompt, null);
+	}
+
+	public Flux<ChatResponse> internalStream(Prompt prompt, ChatResponse previousChatResponse) {
 		return Flux.deferContextual(contextView -> {
 			var request = createRequest(prompt, true);
 
@@ -258,7 +282,9 @@ public Flux<ChatResponse> stream(Prompt prompt) {
 							// @formatter:on
 
 						if (chatCompletion2.usage() != null) {
-							return new ChatResponse(generations, from(chatCompletion2));
+							MistralAiUsage usage = MistralAiUsage.from(chatCompletion2.usage());
+							Usage cumulativeUsage = UsageUtils.getCumulativeUsage(usage, previousChatResponse);
+							return new ChatResponse(generations, from(chatCompletion2, cumulativeUsage));
 						}
 						else {
 							return new ChatResponse(generations);
@@ -276,7 +302,7 @@ public Flux<ChatResponse> stream(Prompt prompt) {
 					var toolCallConversation = handleToolCalls(prompt, response);
 					// Recursively call the stream method with the tool call message
 					// conversation that contains the call responses.
-					return this.stream(new Prompt(toolCallConversation, prompt.getOptions()));
+					return this.internalStream(new Prompt(toolCallConversation, prompt.getOptions()), response);
 				}
 				else {
 					return Flux.just(response);
@@ -313,7 +339,8 @@ private ChatCompletion toChatCompletion(ChatCompletionChunk chunk) {
 			.map(cc -> new Choice(cc.index(), cc.delta(), cc.finishReason(), cc.logprobs()))
 			.toList();
 
-		return new ChatCompletion(chunk.id(), "chat.completion", chunk.created(), chunk.model(), choices, null);
+		return new ChatCompletion(chunk.id(), "chat.completion", chunk.created(), chunk.model(), choices,
+				chunk.usage());
 	}
 
 	/**

models/spring-ai-mistral-ai/src/main/java/org/springframework/ai/mistralai/api/MistralAiApi.java

@@ -209,7 +209,8 @@ public Flux<ChatCompletionChunk> chatCompletionStream(ChatCompletionRequest chat
 				return !isInsideTool.get();
 			})
 			.concatMapIterable(window -> {
-				Mono<ChatCompletionChunk> mono1 = window.reduce(new ChatCompletionChunk(null, null, null, null, null),
+				Mono<ChatCompletionChunk> mono1 = window.reduce(
+						new ChatCompletionChunk(null, null, null, null, null, null),
 						(previous, current) -> this.chunkMerger.merge(previous, current));
 				return List.of(mono1);
 			})
@@ -934,6 +935,7 @@ public record TopLogProbs(@JsonProperty("token") String token, @JsonProperty("lo
 	 * @param model The model used for the chat completion.
 	 * @param choices A list of chat completion choices. Can be more than one if n is
 	 * greater than 1.
+	 * @param usage usage metrics for the chat completion.
 	 */
 	@JsonInclude(Include.NON_NULL)
 	public record ChatCompletionChunk(
@@ -942,7 +944,8 @@ public record ChatCompletionChunk(
 		@JsonProperty("object") String object,
 		@JsonProperty("created") Long created,
 		@JsonProperty("model") String model,
-		@JsonProperty("choices") List<ChunkChoice> choices) {
+		@JsonProperty("choices") List<ChunkChoice> choices,
+		@JsonProperty("usage") Usage usage) {
 		 // @formatter:on
 
 		/**

models/spring-ai-mistral-ai/src/main/java/org/springframework/ai/mistralai/api/MistralAiStreamFunctionCallingHelper.java

@@ -63,7 +63,9 @@ public ChatCompletionChunk merge(ChatCompletionChunk previous, ChatCompletionChu
 
 		ChunkChoice choice = merge(previousChoice0, currentChoice0);
 
-		return new ChatCompletionChunk(id, object, created, model, List.of(choice));
+		MistralAiApi.Usage usage = (current.usage() != null ? current.usage() : previous.usage());
+
+		return new ChatCompletionChunk(id, object, created, model, List.of(choice), usage);
 	}
 
 	private ChunkChoice merge(ChunkChoice previous, ChunkChoice current) {

models/spring-ai-mistral-ai/src/test/java/org/springframework/ai/mistralai/MistralAiChatModelIT.java

@@ -205,6 +205,9 @@ void functionCallTest() {
 		logger.info("Response: {}", response);
 
 		assertThat(response.getResult().getOutput().getText()).containsAnyOf("30.0", "30");
+		assertThat(response.getMetadata()).isNotNull();
+		assertThat(response.getMetadata().getUsage()).isNotNull();
+		assertThat(response.getMetadata().getUsage().getTotalTokens()).isLessThan(1050).isGreaterThan(800);
 	}
 
 	@Test
@@ -238,6 +241,32 @@ void streamFunctionCallTest() {
 		assertThat(content).containsAnyOf("10.0", "10");
 	}
 
+	@Test
+	void streamFunctionCallUsageTest() {
+
+		UserMessage userMessage = new UserMessage(
+				"What's the weather like in San Francisco, Tokyo, and Paris? Response in Celsius");
+
+		List<Message> messages = new ArrayList<>(List.of(userMessage));
+
+		var promptOptions = MistralAiChatOptions.builder()
+			.withModel(MistralAiApi.ChatModel.SMALL.getValue())
+			.withFunctionCallbacks(List.of(FunctionCallback.builder()
+				.function("getCurrentWeather", new MockWeatherService())
+				.description("Get the weather in location")
+				.inputType(MockWeatherService.Request.class)
+				.build()))
+			.build();
+
+		Flux<ChatResponse> response = this.streamingChatModel.stream(new Prompt(messages, promptOptions));
+		ChatResponse chatResponse = response.last().block();
+
+		logger.info("Response: {}", chatResponse);
+		assertThat(chatResponse.getMetadata()).isNotNull();
+		assertThat(chatResponse.getMetadata().getUsage()).isNotNull();
+		assertThat(chatResponse.getMetadata().getUsage().getTotalTokens()).isLessThan(1050).isGreaterThan(800);
+	}
+
 	record ActorsFilmsRecord(String actor, List<String> movies) {
 
 	}

models/spring-ai-mistral-ai/src/test/java/org/springframework/ai/mistralai/MistralAiRetryTests.java

@@ -124,7 +124,7 @@ public void mistralAiChatStreamTransientError() {
 		var choice = new ChatCompletionChunk.ChunkChoice(0, new ChatCompletionMessage("Response", Role.ASSISTANT),
 				ChatCompletionFinishReason.STOP, null);
 		ChatCompletionChunk expectedChatCompletion = new ChatCompletionChunk("id", "chat.completion.chunk", 789L,
-				"model", List.of(choice));
+				"model", List.of(choice), null);
 
 		given(this.mistralAiApi.chatCompletionStream(isA(ChatCompletionRequest.class)))
 			.willThrow(new TransientAiException("Transient Error 1"))