package ai

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

	"github.com/sundynix/pets-be/internal/config"
)

// openaiCompatProvider 走 OpenAI 兼容的 /chat/completions 协议。
// DeepSeek、Qwen(dashscope 兼容模式)、Moonshot、Gemini(OpenAI 兼容端点) 等均可用。
type openaiCompatProvider struct {
	baseURL string
	apiKey  string
	model   string
	client  *http.Client
}

func newOpenAICompatProvider(cfg config.AIConfig) *openaiCompatProvider {
	timeout := time.Duration(cfg.TimeoutSec) * time.Second
	if timeout <= 0 {
		timeout = 30 * time.Second
	}
	return &openaiCompatProvider{
		baseURL: strings.TrimRight(cfg.BaseURL, "/"),
		apiKey:  cfg.APIKey,
		model:   cfg.Model,
		client:  &http.Client{Timeout: timeout},
	}
}

func (p *openaiCompatProvider) Name() string { return "openai-compat:" + p.model }

type chatReq struct {
	Model          string      `json:"model"`
	Messages       []chatMsg   `json:"messages"`
	Temperature    float64     `json:"temperature,omitempty"`
	MaxTokens      int         `json:"max_tokens,omitempty"`
	ResponseFormat *respFormat `json:"response_format,omitempty"`
}

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

type respFormat struct {
	Type string `json:"type"`
}

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

func (p *openaiCompatProvider) Complete(system string, messages []Message, opts Options) (string, error) {
	msgs := make([]chatMsg, 0, len(messages)+1)
	if system != "" {
		msgs = append(msgs, chatMsg{Role: "system", Content: system})
	}
	for _, m := range messages {
		msgs = append(msgs, chatMsg{Role: m.Role, Content: m.Content})
	}

	body := chatReq{
		Model:       p.model,
		Messages:    msgs,
		Temperature: opts.Temperature,
		MaxTokens:   opts.MaxTokens,
	}
	if opts.JSON {
		body.ResponseFormat = &respFormat{Type: "json_object"}
	}
	raw, _ := json.Marshal(body)

	ctx, cancel := context.WithTimeout(context.Background(), p.client.Timeout)
	defer cancel()
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, p.baseURL+"/chat/completions", bytes.NewReader(raw))
	if err != nil {
		return "", err
	}
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("Authorization", "Bearer "+p.apiKey)

	resp, err := p.client.Do(req)
	if err != nil {
		return "", err
	}
	defer resp.Body.Close()

	data, _ := io.ReadAll(resp.Body)
	var out chatResp
	if err := json.Unmarshal(data, &out); err != nil {
		return "", fmt.Errorf("ai 响应解析失败: %s", truncate(string(data), 200))
	}
	if out.Error != nil {
		return "", fmt.Errorf("ai 供应商错误: %s", out.Error.Message)
	}
	if resp.StatusCode >= 400 || len(out.Choices) == 0 {
		return "", fmt.Errorf("ai 调用失败(%d): %s", resp.StatusCode, truncate(string(data), 200))
	}
	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]
}