Refactor role handling in OpenAI request processing for improved clarity and functionality

internal/translator/gemini-cli/openai/cli_openai_request.go

@@ -94,9 +94,10 @@ func ConvertOpenAIChatRequestToCli(rawJSON []byte) (string, *client.Content, []c
 				continue
 			}
 
-			switch roleResult.String() {
+			role := roleResult.String()
+
+			if role == "system" && len(messagesResults) > 1 {
 				// System messages are converted to a user message followed by a model's acknowledgment.
-			case "system":
 				if contentResult.Type == gjson.String {
 					systemInstruction = &client.Content{Role: "user", Parts: []client.Part{{Text: contentResult.String()}}}
 				} else if contentResult.IsObject() {
@@ -105,8 +106,8 @@ func ConvertOpenAIChatRequestToCli(rawJSON []byte) (string, *client.Content, []c
 						systemInstruction = &client.Content{Role: "user", Parts: []client.Part{{Text: contentResult.Get("text").String()}}}
 					}
 				}
+			} else if role == "user" || (role == "system" && len(messagesResults) == 1) { // If there's only a system message, treat it as a user message.
 				// User messages can contain simple text or a multi-part body.
-			case "user":
 				if contentResult.Type == gjson.String {
 					contents = append(contents, client.Content{Role: "user", Parts: []client.Part{{Text: contentResult.String()}}})
 				} else if contentResult.IsArray() {
@@ -151,9 +152,10 @@ func ConvertOpenAIChatRequestToCli(rawJSON []byte) (string, *client.Content, []c
 					}
 					contents = append(contents, client.Content{Role: "user", Parts: parts})
 				}
+			} else if role == "assistant" {
 				// Assistant messages can contain text responses or tool calls
 				// In the internal format, assistant messages are converted to "model" role
-			case "assistant":
+
 				if contentResult.Type == gjson.String {
 					// Simple text response from the assistant
 					contents = append(contents, client.Content{Role: "model", Parts: []client.Part{{Text: contentResult.String()}}})