lmcli/pkg/api/provider/openai/openai.go

package openai

import (
	"bufio"
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"strings"

	"git.mlow.ca/mlow/lmcli/pkg/api"
)

type OpenAIClient struct {
	APIKey  string
	BaseURL string
}

type ChatCompletionMessage struct {
	Role       string     `json:"role"`
	Content    string     `json:"content,omitempty"`
	ToolCalls  []ToolCall `json:"tool_calls,omitempty"`
	ToolCallID string     `json:"tool_call_id,omitempty"`
}

type ToolCall struct {
	Type     string             `json:"type"`
	ID       string             `json:"id"`
	Index    *int               `json:"index,omitempty"`
	Function FunctionDefinition `json:"function"`
}

type FunctionDefinition struct {
	Name        string         `json:"name"`
	Description string         `json:"description"`
	Parameters  ToolParameters `json:"parameters"`
	Arguments   string         `json:"arguments,omitempty"`
}

type ToolParameters struct {
	Type       string                   `json:"type"`
	Properties map[string]ToolParameter `json:"properties,omitempty"`
	Required   []string                 `json:"required,omitempty"`
}

type ToolParameter struct {
	Type        string   `json:"type"`
	Description string   `json:"description"`
	Enum        []string `json:"enum,omitempty"`
}

type Tool struct {
	Type     string             `json:"type"`
	Function FunctionDefinition `json:"function"`
}

type ChatCompletionRequest struct {
	Model       string                  `json:"model"`
	MaxTokens   int                     `json:"max_tokens,omitempty"`
	Temperature float32                 `json:"temperature,omitempty"`
	Messages    []ChatCompletionMessage `json:"messages"`
	N           int                     `json:"n"`
	Tools       []Tool                  `json:"tools,omitempty"`
	ToolChoice  string                  `json:"tool_choice,omitempty"`
	Stream      bool                    `json:"stream,omitempty"`
}

type ChatCompletionChoice struct {
	Message ChatCompletionMessage `json:"message"`
}

type ChatCompletionResponse struct {
	Choices []ChatCompletionChoice `json:"choices"`
}

type ChatCompletionStreamChoice struct {
	Delta ChatCompletionMessage `json:"delta"`
}

type ChatCompletionStreamResponse struct {
	Choices []ChatCompletionStreamChoice `json:"choices"`
}

func convertTools(tools []api.ToolSpec) []Tool {
	openaiTools := make([]Tool, len(tools))
	for i, tool := range tools {
		openaiTools[i].Type = "function"

		params := make(map[string]ToolParameter)
		var required []string

		for _, param := range tool.Parameters {
			params[param.Name] = ToolParameter{
				Type:        param.Type,
				Description: param.Description,
				Enum:        param.Enum,
			}
			if param.Required {
				required = append(required, param.Name)
			}
		}

		openaiTools[i].Function = FunctionDefinition{
			Name:        tool.Name,
			Description: tool.Description,
			Parameters: ToolParameters{
				Type:       "object",
				Properties: params,
				Required:   required,
			},
		}
	}
	return openaiTools
}

func convertToolCallToOpenAI(toolCalls []api.ToolCall) []ToolCall {
	converted := make([]ToolCall, len(toolCalls))
	for i, call := range toolCalls {
		converted[i].Type = "function"
		converted[i].ID = call.ID
		converted[i].Function.Name = call.Name

		json, _ := json.Marshal(call.Parameters)
		converted[i].Function.Arguments = string(json)
	}
	return converted
}

func convertToolCallToAPI(toolCalls []ToolCall) []api.ToolCall {
	converted := make([]api.ToolCall, len(toolCalls))
	for i, call := range toolCalls {
		converted[i].ID = call.ID
		converted[i].Name = call.Function.Name
		json.Unmarshal([]byte(call.Function.Arguments), &converted[i].Parameters)
	}
	return converted
}

func createChatCompletionRequest(
	params api.RequestParameters,
	messages []api.Message,
) ChatCompletionRequest {
	requestMessages := make([]ChatCompletionMessage, 0, len(messages))

	for _, m := range messages {
		switch m.Role {
		case "tool_call":
			message := ChatCompletionMessage{}
			message.Role = "assistant"
			message.Content = m.Content
			message.ToolCalls = convertToolCallToOpenAI(m.ToolCalls)
			requestMessages = append(requestMessages, message)
		case "tool_result":
			// expand tool_result messages' results into multiple openAI messages
			for _, result := range m.ToolResults {
				message := ChatCompletionMessage{}
				message.Role = "tool"
				message.Content = result.Result
				message.ToolCallID = result.ToolCallID
				requestMessages = append(requestMessages, message)
			}
		default:
			message := ChatCompletionMessage{}
			message.Role = string(m.Role)
			message.Content = m.Content
			requestMessages = append(requestMessages, message)
		}
	}

	request := ChatCompletionRequest{
		Model:       params.Model,
		MaxTokens:   params.MaxTokens,
		Temperature: params.Temperature,
		Messages:    requestMessages,
		N:           1, // limit responses to 1 "choice". we use choices[0] to reference it
	}

	if len(params.ToolBag) > 0 {
		request.Tools = convertTools(params.ToolBag)
		request.ToolChoice = "auto"
	}

	return request
}

func (c *OpenAIClient) sendRequest(ctx context.Context, r ChatCompletionRequest) (*http.Response, error) {
	jsonData, err := json.Marshal(r)
	if err != nil {
		return nil, err
	}

	req, err := http.NewRequestWithContext(ctx, "POST", c.BaseURL+"/v1/chat/completions", bytes.NewBuffer(jsonData))
	if err != nil {
		return nil, err
	}

	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("Authorization", "Bearer "+c.APIKey)

	client := &http.Client{}
	resp, err := client.Do(req)
	if err != nil {
		return nil, err
	}

	if resp.StatusCode != 200 {
		bytes, _ := io.ReadAll(resp.Body)
		return resp, fmt.Errorf("%v", string(bytes))
	}

	return resp, err
}

func (c *OpenAIClient) CreateChatCompletion(
	ctx context.Context,
	params api.RequestParameters,
	messages []api.Message,
) (*api.Message, error) {
	if len(messages) == 0 {
		return nil, fmt.Errorf("Can't create completion from no messages")
	}

	req := createChatCompletionRequest(params, messages)

	resp, err := c.sendRequest(ctx, req)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()

	var completionResp ChatCompletionResponse
	err = json.NewDecoder(resp.Body).Decode(&completionResp)
	if err != nil {
		return nil, err
	}

	choice := completionResp.Choices[0]

	var content string
	lastMessage := messages[len(messages)-1]
	if lastMessage.Role.IsAssistant() {
		content = lastMessage.Content + choice.Message.Content
	} else {
		content = choice.Message.Content
	}

	toolCalls := choice.Message.ToolCalls
	if len(toolCalls) > 0 {
		return &api.Message{
			Role:      api.MessageRoleToolCall,
			Content:   content,
			ToolCalls: convertToolCallToAPI(toolCalls),
		}, nil
	}

	return &api.Message{
		Role:    api.MessageRoleAssistant,
		Content: content,
	}, nil
}

func (c *OpenAIClient) CreateChatCompletionStream(
	ctx context.Context,
	params api.RequestParameters,
	messages []api.Message,
	output chan<- api.Chunk,
) (*api.Message, error) {
	if len(messages) == 0 {
		return nil, fmt.Errorf("Can't create completion from no messages")
	}

	req := createChatCompletionRequest(params, messages)
	req.Stream = true

	resp, err := c.sendRequest(ctx, req)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()

	content := strings.Builder{}
	toolCalls := []ToolCall{}

	lastMessage := messages[len(messages)-1]
	if lastMessage.Role.IsAssistant() {
		content.WriteString(lastMessage.Content)
	}

	reader := bufio.NewReader(resp.Body)
	for {
		line, err := reader.ReadBytes('\n')
		if err != nil {
			if err == io.EOF {
				break
			}
			return nil, err
		}

		line = bytes.TrimSpace(line)
		if len(line) == 0 || !bytes.HasPrefix(line, []byte("data: ")) {
			continue
		}

		line = bytes.TrimPrefix(line, []byte("data: "))
		if bytes.Equal(line, []byte("[DONE]")) {
			break
		}

		var streamResp ChatCompletionStreamResponse
		err = json.Unmarshal(line, &streamResp)
		if err != nil {
			return nil, err
		}

		delta := streamResp.Choices[0].Delta
		if len(delta.ToolCalls) > 0 {
			// Construct streamed tool_call arguments
			for _, tc := range delta.ToolCalls {
				if tc.Index == nil {
					return nil, fmt.Errorf("Unexpected nil index for streamed tool call.")
				}
				if len(toolCalls) <= *tc.Index {
					toolCalls = append(toolCalls, tc)
				} else {
					toolCalls[*tc.Index].Function.Arguments += tc.Function.Arguments
				}
			}
		}
		if len(delta.Content) > 0 {
			output <- api.Chunk{
				Content:    delta.Content,
				TokenCount: 1,
			}
			content.WriteString(delta.Content)
		}
	}

	if len(toolCalls) > 0 {
		return &api.Message{
			Role:      api.MessageRoleToolCall,
			Content:   content.String(),
			ToolCalls: convertToolCallToAPI(toolCalls),
		}, nil
	}

	return &api.Message{
		Role:    api.MessageRoleAssistant,
		Content: content.String(),
	}, nil
}