// Package ai provides a tiny OpenAI chat client (stdlib only) for short mail
// summaries. Disabled (no-op) when no API key is configured.
package ai

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

type Client struct {
	key   string
	model string
	http  *http.Client
}

func New(apiKey string) *Client {
	return &Client{key: strings.TrimSpace(apiKey), model: "gpt-4o-mini", http: &http.Client{Timeout: 20 * time.Second}}
}

func (c *Client) Enabled() bool { return c != nil && c.key != "" }

// Summarize returns a one-line Korean summary of the text. Best-effort; returns
// an error the caller can ignore (summary stays empty).
func (c *Client) Summarize(ctx context.Context, text string) (string, error) {
	if !c.Enabled() {
		return "", nil
	}
	text = strings.TrimSpace(text)
	if text == "" {
		return "", nil
	}
	if len(text) > 4000 {
		text = text[:4000]
	}
	body := map[string]any{
		"model": c.model,
		"messages": []map[string]string{
			{"role": "system", "content": "너는 이메일을 아주 짧게 요약하는 비서다. 한국어로 핵심만 한 문장(최대 40자)으로 답하라. 군더더기·인사말 제외."},
			{"role": "user", "content": text},
		},
		"max_tokens":  80,
		"temperature": 0.2,
	}
	b, _ := json.Marshal(body)
	req, _ := http.NewRequestWithContext(ctx, http.MethodPost, "https://api.openai.com/v1/chat/completions", bytes.NewReader(b))
	req.Header.Set("Authorization", "Bearer "+c.key)
	req.Header.Set("Content-Type", "application/json")
	resp, err := c.http.Do(req)
	if err != nil {
		return "", err
	}
	defer resp.Body.Close()
	if resp.StatusCode >= 300 {
		return "", fmt.Errorf("openai %d", resp.StatusCode)
	}
	var out struct {
		Choices []struct {
			Message struct {
				Content string `json:"content"`
			} `json:"message"`
		} `json:"choices"`
	}
	if err := json.NewDecoder(resp.Body).Decode(&out); err != nil {
		return "", err
	}
	if len(out.Choices) == 0 {
		return "", nil
	}
	return strings.TrimSpace(out.Choices[0].Message.Content), nil
}