// Package llm OpenAI 兼容 Chat 客户端（移植自 opsx-jenkins 生产实现）。
package llm

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

type Client struct {
	Endpoint  string
	APIKey    string
	Model     string
	MaxTokens int
}

func NewClient(endpoint, apiKey, model string, maxTokens int) *Client {
	if maxTokens <= 0 {
		maxTokens = 1200
	}
	return &Client{
		Endpoint:  strings.TrimRight(endpoint, "/"),
		APIKey:    apiKey,
		Model:     model,
		MaxTokens: maxTokens,
	}
}

type chatMessage struct {
	Role    string `json:"role"`
	Content string `json:"content"`
}

type chatRequest struct {
	Model       string        `json:"model"`
	Messages    []chatMessage `json:"messages"`
	Temperature float64       `json:"temperature"`
	MaxTokens   int           `json:"max_tokens"`
	Stream      bool          `json:"stream,omitempty"`
}

type chatResponse struct {
	Choices []struct {
		Message struct {
			Content string `json:"content"`
		} `json:"message"`
	} `json:"choices"`
	Error *struct {
		Message string `json:"message"`
	} `json:"error"`
}

// Chat 单轮对话；endpoint/apiKey 为空时返回错误由调用方降级
func (c *Client) Chat(ctx context.Context, system, user string) (string, error) {
	if c.Endpoint == "" || c.APIKey == "" || c.Model == "" {
		return "", fmt.Errorf("LLM 未配置")
	}
	payload := chatRequest{
		Model: c.Model,
		Messages: []chatMessage{
			{Role: "system", Content: system},
			{Role: "user", Content: user},
		},
		Temperature: 0.2,
		MaxTokens:   c.MaxTokens,
	}
	body, err := json.Marshal(payload)
	if err != nil {
		return "", err
	}
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, c.Endpoint+"/chat/completions", bytes.NewReader(body))
	if err != nil {
		return "", err
	}
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("Authorization", "Bearer "+c.APIKey)

	resp, err := (&http.Client{Timeout: 90 * time.Second}).Do(req)
	if err != nil {
		return "", err
	}
	defer resp.Body.Close()

	data, err := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
	if err != nil {
		return "", err
	}
	var out chatResponse
	if err := json.Unmarshal(data, &out); err != nil {
		return "", fmt.Errorf("响应解析失败: %s", truncate(string(data), 200))
	}
	if out.Error != nil && out.Error.Message != "" {
		return "", fmt.Errorf("LLM 错误: %s", out.Error.Message)
	}
	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return "", fmt.Errorf("HTTP %d: %s", resp.StatusCode, truncate(string(data), 200))
	}
	if len(out.Choices) == 0 {
		return "", fmt.Errorf("空响应")
	}
	return strings.TrimSpace(out.Choices[0].Message.Content), nil
}

func truncate(s string, n int) string {
	if len(s) <= n {
		return s
	}
	return s[:n] + "..."
}

// StreamDelta 单个流式增量
type StreamDelta struct {
	Content   string // 正文增量
	Reasoning string // 推理过程增量（DeepSeek R1 类模型）
	Usage     *Usage // 最后一个 chunk 可能带用量
}

// Usage token 用量
type Usage struct {
	PromptTokens     int `json:"prompt_tokens"`
	CompletionTokens int `json:"completion_tokens"`
	TotalTokens      int `json:"total_tokens"`
}

type streamChunk struct {
	Choices []struct {
		Delta struct {
			Content      string `json:"content"`
			Reasoning    string `json:"reasoning_content"`
			FinishReason string `json:"finish_reason"`
		} `json:"delta"`
	} `json:"choices"`
	Usage *Usage `json:"usage"`
}

// ChatStream 流式对话：onDelta 逐段回调（正文/推理），返回完整正文。
// 流式请求不设整体超时，由 ctx 控制取消。
func (c *Client) ChatStream(ctx context.Context, system, user string, onDelta func(StreamDelta)) (string, error) {
	if c.Endpoint == "" || c.APIKey == "" || c.Model == "" {
		return "", fmt.Errorf("LLM 未配置")
	}
	payload := chatRequest{
		Model: c.Model,
		Messages: []chatMessage{
			{Role: "system", Content: system},
			{Role: "user", Content: user},
		},
		Temperature: 0.2,
		MaxTokens:   c.MaxTokens,
		Stream:      true,
	}
	body, err := json.Marshal(payload)
	if err != nil {
		return "", err
	}
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, c.Endpoint+"/chat/completions", bytes.NewReader(body))
	if err != nil {
		return "", err
	}
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("Authorization", "Bearer "+c.APIKey)

	// 流式专用 client：Timeout 0，取消由 ctx 控制
	resp, err := (&http.Client{}).Do(req)
	if err != nil {
		return "", err
	}
	defer resp.Body.Close()
	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		data, _ := io.ReadAll(io.LimitReader(resp.Body, 2048))
		return "", fmt.Errorf("HTTP %d: %s", resp.StatusCode, truncate(string(data), 200))
	}

	var full strings.Builder
	scanner := bufio.NewScanner(resp.Body)
	scanner.Buffer(make([]byte, 64*1024), 1024*1024)
	for scanner.Scan() {
		line := strings.TrimSpace(scanner.Text())
		if !strings.HasPrefix(line, "data:") {
			continue
		}
		data := strings.TrimSpace(strings.TrimPrefix(line, "data:"))
		if data == "" || data == "[DONE]" {
			continue
		}
		var chunk streamChunk
		if err := json.Unmarshal([]byte(data), &chunk); err != nil {
			continue
		}
		if len(chunk.Choices) == 0 {
			if chunk.Usage != nil && onDelta != nil {
				onDelta(StreamDelta{Usage: chunk.Usage})
			}
			continue
		}
		d := chunk.Choices[0].Delta
		if d.Content != "" || d.Reasoning != "" {
			full.WriteString(d.Content)
			if onDelta != nil {
				onDelta(StreamDelta{Content: d.Content, Reasoning: d.Reasoning})
			}
		}
	}
	if err := scanner.Err(); err != nil {
		if ctx.Err() != nil {
			return full.String(), nil // 客户端主动取消：返回已收到的内容
		}
		return full.String(), err
	}
	if full.Len() == 0 {
		return "", fmt.Errorf("流式响应为空")
	}
	return full.String(), nil
}