package main

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

// llmChat: 调用百炼 OpenAI 兼容接口，客服机器人人设，流式返回。
func llmChat(ctx context.Context, cfg agentCfg, history []chatMsg) (<-chan string, <-chan error) {
	textCh := make(chan string, 16)
	errCh := make(chan error, 1)

	msgs := make([]chatMsg, 0, len(history)+1)
	msgs = append(msgs, chatMsg{Role: "system", Content: systemPrompt})
	msgs = append(msgs, history...)

	body, _ := json.Marshal(map[string]any{
		"model":    cfg.LLMModel,
		"messages": msgs,
		"stream":   true,
		// qwen3 默认开 thinking（多耗时~0.5s且无播报价值），关掉
		"enable_thinking": false,
	})
	req, err := http.NewRequestWithContext(ctx, "POST", cfg.BailianBaseURL+"/chat/completions",
		bytes.NewReader(body))
	if err != nil {
		close(textCh)
		errCh <- err
		return textCh, errCh
	}
	req.Header.Set("Authorization", "Bearer "+cfg.BailianKey)
	req.Header.Set("Content-Type", "application/json")

	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		close(textCh)
		errCh <- err
		return textCh, errCh
	}

	go func() {
		defer resp.Body.Close()
		defer close(textCh)
		if resp.StatusCode != 200 {
			b := new(bytes.Buffer)
			b.ReadFrom(resp.Body)
			errCh <- fmt.Errorf("LLM %s: %s", resp.Status, b.String())
			return
		}
		sc := bufio.NewScanner(resp.Body)
		sc.Buffer(make([]byte, 64*1024), 1024*1024)
		defer func() { // ponytail: buffered errCh，扫完总能写入，避免读端永久阻塞
			errCh <- sc.Err()
		}()
		for sc.Scan() {
			line := sc.Text()
			if !strings.HasPrefix(line, "data: ") {
				continue
			}
			data := strings.TrimPrefix(line, "data: ")
			if data == "[DONE]" {
				return
			}
			var chunk struct {
				Choices []struct {
					Delta struct {
						Content string `json:"content"`
					} `json:"delta"`
				} `json:"choices"`
			}
			if json.Unmarshal([]byte(data), &chunk) != nil {
				continue
			}
			for _, c := range chunk.Choices {
				if c.Delta.Content != "" {
					textCh <- c.Delta.Content
				}
			}
		}
	}()
	return textCh, errCh
}

const systemPrompt = `你是"小智"，某电商平台的电话客服机器人。规则：
- 用口语化、亲切的中文简短回答，每句不超过两句话，适合语音播报。
- 常见问题直接答：订单查询请提供订单号；退换货支持7天无理由；发货一般48小时内；客服热线工作时间9:00-21:00。
- 超出范围的问题，礼貌说明并引导转人工客服。
- 不要使用 markdown、表情符号或列表编号。`