feat(ToolChoice): refactor chat system and tool selection (#159)

- Add a system chat message with the content "You are a helpful assistant."
- Introduce a new `ToolChoice` structure with `Type` set to `ToolTypeFunction` and `Function` containing the function name.

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

Author: appleboy

openai/openai.go

@@ -108,12 +108,22 @@ func (c *Client) CreateFunctionCall(
 		FrequencyPenalty: c.frequencyPenalty,
 		PresencePenalty:  c.presencePenalty,
 		Messages: []openai.ChatCompletionMessage{
+			{
+				Role:    openai.ChatMessageRoleSystem,
+				Content: "You are a helpful assistant.",
+			},
 			{
 				Role:    openai.ChatMessageRoleUser,
 				Content: content,
 			},
 		},
 		Tools: []openai.Tool{t},
+		ToolChoice: openai.ToolChoice{
+			Type: openai.ToolTypeFunction,
+			Function: openai.ToolFunction{
+				Name: f.Name,
+			},
+		},
 	}
 
 	return c.client.CreateChatCompletion(ctx, req)