package smtp

import (
	"bytes"
	"errors"
	"fmt"
	"net/textproto"
	"strings"
	"time"
)

type Message struct {
	Subject    string   // 主题
	To         []string // 主送
	Cc         []string // 抄送
	Bcc        []string // 密送
	Body       []byte   // 内容
	recipients []string // 主送+抄送+密送
}

func (own *Message) GeneateText(form string) ([]byte, error) {
	if err := own.Validate(); err != nil {
		return nil, err
	}

	var buf bytes.Buffer

	// 构建邮件头
	headers := make(textproto.MIMEHeader)
	headers.Set("From", form)
	headers.Set("To", strings.Join(own.To, ", "))

	// 添加抄送头
	if len(own.Cc) > 0 {
		headers.Set("Cc", strings.Join(own.Cc, ", "))
	}

	headers.Set("Subject", own.Subject)
	headers.Set("Content-Type", "multipart/mixed; boundary=\"BOUNDARY\"")
	headers.Set("MIME-Version", "1.0")
	headers.Set("Date", time.Now().Format(time.RFC1123Z))

	// 写入邮件头
	for k, v := range headers {
		buf.WriteString(fmt.Sprintf("%s: %s\r\n", k, v[0]))
	}
	buf.WriteString("\r\n")

	// 写入邮件正文部分
	buf.WriteString("--BOUNDARY\r\n")
	buf.WriteString("Content-Type: text/plain; charset=utf-8\r\n\r\n")
	buf.Write(own.Body)
	buf.WriteString("\r\n\r\n")

	// 结束边界
	buf.WriteString("\r\n--BOUNDARY--\r\n")

	return buf.Bytes(), nil
}

func (own *Message) GeneateHTML(form string) ([]byte, error) {
	if err := own.Validate(); err != nil {
		return nil, err
	}

	// 创建MIME边界
	boundary := "----=_NextPart_" + fmt.Sprintf("%x", time.Now().UnixNano())

	var buf bytes.Buffer

	// 构建邮件头
	headers := make(textproto.MIMEHeader)
	headers.Set("From", form)
	headers.Set("To", strings.Join(own.To, ", "))

	// 添加抄送头
	if len(own.Cc) > 0 {
		headers.Set("Cc", strings.Join(own.Cc, ", "))
	}

	headers.Set("Subject", own.Subject)
	headers.Set("MIME-Version", "1.0")
	headers.Set("Content-Type", "multipart/alternative; boundary=\""+boundary+"\"")
	headers.Set("X-Mailer", "GoMailer")
	headers.Set("X-Priority", "1 (Highest)")

	// 写入邮件头
	for k, v := range headers {
		buf.WriteString(fmt.Sprintf("%s: %s\r\n", k, v[0]))
	}
	buf.WriteString("\r\n")

	// 写入邮件正文部分
	buf.WriteString("--" + boundary + "\r\n")
	buf.WriteString("Content-Type: text/html; charset=UTF-8\r\n")
	buf.WriteString("Content-Transfer-Encoding: quoted-printable\r\n")
	buf.WriteString("\r\n")
	buf.Write(own.Body)
	buf.WriteString("\r\n")

	// 结束边界
	buf.WriteString("--" + boundary + "--\r\n")

	return buf.Bytes(), nil
}

var (
	errEmptySubject = errors.New("smtp: 'Subject' is empty")
	errEmptyTo      = errors.New("smtp: 'To' is empty")
)

func (own *Message) Validate() error {
	if own.Subject == "" {
		return errEmptySubject
	}

	own.recipients = make([]string, 0)
	if len(own.To) == 0 {
		return errEmptyTo
	}
	own.recipients = append(own.recipients, own.To...)

	if len(own.Cc) > 0 {
		own.recipients = append(own.recipients, own.Cc...)
	}

	if len(own.Bcc) > 0 {
		own.recipients = append(own.recipients, own.Bcc...)
	}

	return nil
}