package email

import (
	"bytes"
	"encoding/base64"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"os"
	"time"
)

// resendEndpoint Resend 发信 API（走 HTTPS/443，规避国内出口 SMTP 被限速/信誉差导致的海外送达率问题）。
const resendEndpoint = "https://api.resend.com/emails"

// Resend 通过 Resend HTTP API 发信，实现 ISys。
// 复用 Options.Password 承载 API Key（re_ 开头）；Options.FromEmail 须为在 Resend 已验证域名下的发件地址。
type Resend struct {
	ApiKey string
	From   string
	Name   string
}

// resendAttachment Resend 附件：内容为 base64 编码。
type resendAttachment struct {
	Filename string `json:"filename"`
	Content  string `json:"content"`
}

// resendPayload Resend /emails 请求体。
type resendPayload struct {
	From        string             `json:"from"`
	To          []string           `json:"to"`
	Subject     string             `json:"subject"`
	Html        string             `json:"html"`
	Attachments []resendAttachment `json:"attachments,omitempty"`
}

var resendClient = &http.Client{Timeout: 15 * time.Second}

// fromAddr 拼成 "昵称 <邮箱>"（无昵称则仅邮箱）。
func (this *Resend) fromAddr() string {
	if this.Name != "" {
		return fmt.Sprintf("%s <%s>", this.Name, this.From)
	}
	return this.From
}

// send 提交一次发信请求，非 2xx 视为失败并带回响应体。
func (this *Resend) send(p *resendPayload) error {
	body, err := json.Marshal(p)
	if err != nil {
		return err
	}
	req, err := http.NewRequest(http.MethodPost, resendEndpoint, bytes.NewReader(body))
	if err != nil {
		return err
	}
	req.Header.Set("Authorization", "Bearer "+this.ApiKey)
	req.Header.Set("Content-Type", "application/json")
	resp, err := resendClient.Do(req)
	if err != nil {
		return err
	}
	defer resp.Body.Close()
	rb, _ := io.ReadAll(resp.Body)
	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return fmt.Errorf("resend send failed: status=%d body=%s", resp.StatusCode, string(rb))
	}
	return nil
}

// SendMail 发送 HTML 邮件。
func (this *Resend) SendMail(title, content string, to ...string) error {
	return this.send(&resendPayload{
		From:    this.fromAddr(),
		To:      to,
		Subject: title,
		Html:    content,
	})
}

// SendMailForFile 发送带单个附件的 HTML 邮件。
func (this *Resend) SendMailForFile(title string, content string, filepath string, filename string, to ...string) (err error) {
	data, err := os.ReadFile(filepath)
	if err != nil {
		return err
	}
	return this.send(&resendPayload{
		From:    this.fromAddr(),
		To:      to,
		Subject: title,
		Html:    content,
		Attachments: []resendAttachment{{
			Filename: filename,
			Content:  base64.StdEncoding.EncodeToString(data),
		}},
	})
}