opencatd-open/backend/internal/proxy/convert/chat_messages.go

package convert

import (
	"encoding/json"
	"fmt"
)

// ChatToMessages converts a Chat Completions request to Anthropic Messages format
func ChatToMessages(req *ChatCompletionRequest) (*MessagesRequest, error) {
	msgs := make([]Message, 0, len(req.Messages))
	var systemParts []ContentPart

	for _, m := range req.Messages {
		if m.Role == "system" {
			// Extract system message content
			switch v := m.Content.(type) {
			case string:
				systemParts = append(systemParts, ContentPart{
					Type: "text",
					Text: v,
				})
			case []interface{}:
				for _, part := range v {
					if p, ok := part.(map[string]interface{}); ok {
						if t, ok := p["type"].(string); ok && t == "text" {
							if text, ok := p["text"].(string); ok {
								systemParts = append(systemParts, ContentPart{
									Type: "text",
									Text: text,
								})
							}
						}
					}
				}
			}
			continue
		}
		msgs = append(msgs, m)
	}

	out := &MessagesRequest{
		Model:     req.Model,
		Messages:  msgs,
		Stream:    req.Stream,
	}

	if len(systemParts) > 0 {
		out.System = systemParts
	}

	if req.MaxTokens != nil {
		out.MaxTokens = *req.MaxTokens
	} else {
		defaultMax := 4096
		out.MaxTokens = defaultMax
	}

	if req.Temperature != nil {
		out.Temperature = req.Temperature
	}
	if req.TopP != nil {
		out.TopP = req.TopP
	}
	if req.Tools != nil {
		out.Tools = req.Tools
	}

	return out, nil
}

// MessagesToChat converts an Anthropic Messages response to Chat Completions format
func MessagesToChat(resp *MessagesResponse) (*ChatCompletionResponse, error) {
	choices := make([]Choice, 0)

	for _, block := range resp.Content {
		switch block.Type {
		case "text":
			choices = append(choices, Choice{
				Index: len(choices),
				Message: Message{
					Role:    "assistant",
					Content: block.Text,
				},
				FinishReason: mapStopReason(resp.StopReason),
			})
		case "tool_use":
			toolCall := ToolCall{
				ID:   block.ID,
				Type: "function",
				Function: FunctionCall{
					Name:      block.Name,
					Arguments: toJSON(block.Input),
				},
			}
			if len(choices) == 0 {
				choices = append(choices, Choice{
					Index: 0,
					Message: Message{
						Role:      "assistant",
						ToolCalls: []ToolCall{toolCall},
					},
					FinishReason: "tool_calls",
				})
			} else {
				choices[0].Message.ToolCalls = append(choices[0].Message.ToolCalls, toolCall)
				choices[0].FinishReason = "tool_calls"
			}
		}
	}

	if len(choices) == 0 {
		choices = append(choices, Choice{
			Index: 0,
			Message: Message{
				Role:    "assistant",
				Content: "",
			},
			FinishReason: "stop",
		})
	}

	return &ChatCompletionResponse{
		ID:      resp.ID,
		Object:  "chat.completion",
		Model:   resp.Model,
		Choices: choices,
		Usage: &Usage{
			PromptTokens:     resp.Usage.PromptTokens,
			CompletionTokens: resp.Usage.CompletionTokens,
			TotalTokens:      resp.Usage.PromptTokens + resp.Usage.CompletionTokens,
		},
	}, nil
}

// MessagesStreamToChatStream converts Anthropic streaming chunks to Chat Completions format
func MessagesStreamToChatStream(anthropicEvents []AnthropicStreamEvent, model string) []ChatCompletionStreamChunk {
	var chunks []ChatCompletionStreamChunk
	id := fmt.Sprintf("chatcmpl-%d", len(anthropicEvents))

	for _, event := range anthropicEvents {
		switch event.Type {
		case "message_start":
			// Initial chunk with role
			chunks = append(chunks, ChatCompletionStreamChunk{
				ID:      id,
				Object:  "chat.completion.chunk",
				Model:   model,
				Choices: []StreamChoice{{
					Index: 0,
					Delta: StreamDelta{
						Role: "assistant",
					},
				}},
			})
		case "content_block_delta":
			if event.Delta != nil && event.Delta.Text != "" {
				chunks = append(chunks, ChatCompletionStreamChunk{
					ID:      id,
					Object:  "chat.completion.chunk",
					Model:   model,
					Choices: []StreamChoice{{
						Index: 0,
						Delta: StreamDelta{
							Content: event.Delta.Text,
						},
					}},
				})
			}
		case "message_delta":
			finishReason := "stop"
			if event.Delta != nil && event.Delta.StopReason != "" {
				finishReason = mapStopReason(event.Delta.StopReason)
			}
			chunk := ChatCompletionStreamChunk{
				ID:      id,
				Object:  "chat.completion.chunk",
				Model:   model,
				Choices: []StreamChoice{{
					Index:        0,
					FinishReason: &finishReason,
				}},
			}
			if event.Usage != nil {
				chunk.Usage = event.Usage
			}
			chunks = append(chunks, chunk)
		}
	}

	return chunks
}

func mapStopReason(reason string) string {
	switch reason {
	case "end_turn", "stop_sequence":
		return "stop"
	case "tool_use":
		return "tool_calls"
	case "max_tokens":
		return "length"
	default:
		return "stop"
	}
}

func toJSON(v interface{}) string {
	b, err := json.Marshal(v)
	if err != nil {
		return "{}"
	}
	return string(b)
}