feat(client): make it easy to roundtrip messages (#148)

Author: stainless-app[bot]

openai-java-core/src/main/kotlin/com/openai/models/ChatCompletionCreateParams.kt

@@ -1413,6 +1413,10 @@ constructor(
                     )
                 )
 
+            /** Messages sent by the model in response to user messages. */
+            fun addMessage(chatCompletionAssistantMessageParam: ChatCompletionMessage) =
+                addMessage(chatCompletionAssistantMessageParam.toParam())
+
             /**
              * A list of messages comprising the conversation so far. Depending on the
              * [model](https://platform.openai.com/docs/models) you use, different message types
@@ -2558,6 +2562,11 @@ constructor(
                 body.addMessage(chatCompletionAssistantMessageParam)
             }
 
+        /** Messages sent by the model in response to user messages. */
+        fun addMessage(chatCompletionAssistantMessageParam: ChatCompletionMessage) = apply {
+            body.addMessage(chatCompletionAssistantMessageParam)
+        }
+
         /**
          * A list of messages comprising the conversation so far. Depending on the
          * [model](https://platform.openai.com/docs/models) you use, different message types

openai-java-core/src/main/kotlin/com/openai/models/ChatCompletionMessage.kt

@@ -103,6 +103,29 @@ private constructor(
     @ExcludeMissing
     fun _additionalProperties(): Map<String, JsonValue> = additionalProperties
 
+    fun toParam(): ChatCompletionAssistantMessageParam =
+        ChatCompletionAssistantMessageParam.builder()
+            .role(_role().map { ChatCompletionAssistantMessageParam.Role.of(it.toString()) })
+            .audio(
+                _audio().map {
+                    ChatCompletionAssistantMessageParam.Audio.builder().id(it._id()).build()
+                }
+            )
+            .content(
+                _content().map { ChatCompletionAssistantMessageParam.Content.ofTextContent(it) }
+            )
+            .functionCall(
+                _functionCall().map {
+                    ChatCompletionAssistantMessageParam.FunctionCall.builder()
+                        .arguments(it._arguments())
+                        .name(it._name())
+                        .build()
+                }
+            )
+            .refusal(_refusal())
+            .toolCalls(_toolCalls())
+            .build()
+
     private var validated: Boolean = false
 
     fun validate(): ChatCompletionMessage = apply {