package gogpt

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

type ChatCompletionStreamChoiceDelta struct {
	Content string `json:"content"`
}

type ChatCompletionStreamChoice struct {
	Index        int                             `json:"index"`
	Delta        ChatCompletionStreamChoiceDelta `json:"delta"`
	FinishReason string                          `json:"finish_reason"`
}

type ChatCompletionStreamResponse struct {
	ID      string                       `json:"id"`
	Object  string                       `json:"object"`
	Created int64                        `json:"created"`
	Model   string                       `json:"model"`
	Choices []ChatCompletionStreamChoice `json:"choices"`
}

// ChatCompletionStream
// Note: Perhaps it is more elegant to abstract Stream using generics.
type ChatCompletionStream struct {
	emptyMessagesLimit uint
	isFinished         bool

	reader   *bufio.Reader
	response *http.Response
}

func (stream *ChatCompletionStream) Recv() (response ChatCompletionStreamResponse, err error) {
	if stream.isFinished {
		err = io.EOF
		return
	}

	var emptyMessagesCount uint

waitForData:
	line, err := stream.reader.ReadBytes('\n')
	if err != nil {
		return
	}

	var headerData = []byte("data: ")
	line = bytes.TrimSpace(line)
	if !bytes.HasPrefix(line, headerData) {
		emptyMessagesCount++
		if emptyMessagesCount > stream.emptyMessagesLimit {
			err = ErrTooManyEmptyStreamMessages
			return
		}

		goto waitForData
	}

	line = bytes.TrimPrefix(line, headerData)
	if string(line) == "[DONE]" {
		stream.isFinished = true
		err = io.EOF
		return
	}

	err = json.Unmarshal(line, &response)
	return
}

func (stream *ChatCompletionStream) Close() {
	stream.response.Body.Close()
}

// CreateChatCompletionStream — API call to create a chat completion w/ streaming
// support. It sets whether to stream back partial progress. If set, tokens will be
// sent as data-only server-sent events as they become available, with the
// stream terminated by a data: [DONE] message.
func (c *Client) CreateChatCompletionStream(
	ctx context.Context,
	request ChatCompletionRequest,
) (stream *ChatCompletionStream, err error) {
	request.Stream = true
	req, err := c.newStreamRequest(ctx, "POST", "/chat/completions", request)
	if err != nil {
		return
	}

	resp, err := c.config.HTTPClient.Do(req) //nolint:bodyclose // body is closed in stream.Close()
	if err != nil {
		return
	}

	stream = &ChatCompletionStream{
		emptyMessagesLimit: c.config.EmptyMessagesLimit,
		reader:             bufio.NewReader(resp.Body),
		response:           resp,
	}
	return
}