package service

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

// AICallConfig holds the resolved configuration for a single AI API call.
type AICallConfig struct {
	BaseURL      string
	APIKey       string
	Model        string
	MaxTokens    int
	SystemPrompt string
}

// ── Request / Response types (OpenAI-compatible format) ──────────────────────

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

type dsRequest struct {
	Model     string      `json:"model"`
	Messages  []dsMessage `json:"messages"`
	Stream    bool        `json:"stream"`
	MaxTokens int         `json:"max_tokens,omitempty"`
}

type dsDelta struct {
	Content string `json:"content"`
}
type dsChoice struct {
	Delta        dsDelta `json:"delta"`
	FinishReason string  `json:"finish_reason"`
}
type dsSSELine struct {
	Choices []dsChoice `json:"choices"`
}

// ── Public API ────────────────────────────────────────────────────────────────

// CallDeepSeekStream sends a messages list to any OpenAI-compatible endpoint
// defined in cfg, with stream:true. Pushes each delta content chunk to streamCh.
func CallDeepSeekStream(ctx context.Context, cfg AICallConfig, messages []dsMessage, streamCh chan<- string) error {
	if cfg.APIKey == "" {
		return fmt.Errorf("API key 未配置，请在设置中填写或联系管理员")
	}

	payload := dsRequest{
		Model:     cfg.Model,
		Messages:  messages,
		Stream:    true,
		MaxTokens: cfg.MaxTokens,
	}
	body, err := json.Marshal(payload)
	if err != nil {
		return fmt.Errorf("marshal request: %w", err)
	}

	client := &http.Client{Timeout: 60 * time.Second}
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, cfg.BaseURL, bytes.NewReader(body))
	if err != nil {
		return fmt.Errorf("build request: %w", err)
	}
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("Accept", "text/event-stream")
	req.Header.Set("Authorization", "Bearer "+cfg.APIKey)

	resp, err := client.Do(req)
	if err != nil {
		if ctx.Err() != nil {
			return ctx.Err()
		}
		return fmt.Errorf("http request: %w", err)
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		errBody, _ := io.ReadAll(resp.Body)
		return fmt.Errorf("upstream status %d: %s", resp.StatusCode, string(errBody))
	}

	return parseDeepSeekSSE(ctx, resp.Body, streamCh)
}

// BuildRAGMessages constructs the OpenAI-compatible messages slice.
// If customSystemPrompt is non-empty, it replaces the built-in RAG template.
func BuildRAGMessages(knowledgeContext, userQuery, customSystemPrompt string) []dsMessage {
	var systemContent string
	if customSystemPrompt != "" {
		systemContent = customSystemPrompt
		if knowledgeContext != "" && knowledgeContext != "(无相关本地知识)" {
			systemContent += "\n\n以下是本地知识库中的相关内容供参考：\n---\n" + knowledgeContext + "\n---"
		}
	} else {
		systemContent = fmt.Sprintf(
			"你是一位专业的植物养护和客服顾问，擅长用温暖、自然、有亲和力的语气沟通。\n\n"+
				"以下是来自本地知识库的相关内容，请优先参考：\n\n---\n%s\n---\n\n"+
				"根据以上知识润色话术，直接输出内容，不加前缀或解释。",
			knowledgeContext,
		)
	}
	return []dsMessage{
		{Role: "system", Content: systemContent},
		{Role: "user", Content: userQuery},
	}
}

func parseDeepSeekSSE(ctx context.Context, body io.Reader, ch chan<- string) error {
	scanner := bufio.NewScanner(body)
	scanner.Buffer(make([]byte, 64*1024), 64*1024)

	for scanner.Scan() {
		if ctx.Err() != nil {
			return ctx.Err()
		}
		line := scanner.Text()
		if !strings.HasPrefix(line, "data:") {
			continue
		}
		data := strings.TrimSpace(strings.TrimPrefix(line, "data:"))
		if data == "[DONE]" {
			break
		}
		var event dsSSELine
		if err := json.Unmarshal([]byte(data), &event); err != nil {
			continue
		}
		if len(event.Choices) > 0 {
			if chunk := event.Choices[0].Delta.Content; chunk != "" {
				ch <- chunk
			}
		}
	}
	return scanner.Err()
}