notification.go

// Copyright 2023 Tomas Machalek <tomas.machalek@gmail.com>
// Copyright 2023 Martin Zimandl <martin.zimandl@gmail.com>
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package mail

import (
	"bytes"
	"fmt"
	"strings"
	"time"

	"github.com/czcorpus/cnc-gokit/datetime"
)

// NotificationConf configures e-mail-based notification
type NotificationConf struct {
	Sender       string   `json:"sender"`
	Recipients   []string `json:"recipients"`
	SMTPServer   string   `json:"smtpServer"`
	SMTPUsername string   `json:"smtpUsername"`
	SMTPPassword string   `json:"smtpPassword"`
	// Signature defines multi-language signature for notification e-mails
	Signature map[string]string `json:"signature"`
}

// WithRecipients creates a new NotificationConf instance
// with recipients overwritten by the provided ones
func (nc NotificationConf) WithRecipients(r ...string) NotificationConf {
	return NotificationConf{
		Sender:       nc.Sender,
		Recipients:   r,
		SMTPServer:   nc.SMTPServer,
		SMTPUsername: nc.SMTPUsername,
		SMTPPassword: nc.SMTPPassword,
		Signature:    nc.Signature,
	}
}

// Notification represents a general notification e-mail
// subject and body.
type Notification struct {
	Subject    string
	Paragraphs []string
}

// SendNotification sends a general e-mail notification.
// Based on configuration, it is able to use SMTP servers
// requiring TLS and authentication (see Dial()).
func SendNotification(conf *NotificationConf, location *time.Location, msg Notification) error {
	client, err := DialServer(conf.SMTPServer, conf.SMTPUsername, conf.SMTPPassword)
	if err != nil {
		return err
	}
	defer client.Close()

	client.Mail(conf.Sender)
	for _, rcpt := range conf.Recipients {
		client.Rcpt(rcpt)
	}

	wc, err := client.Data()
	if err != nil {
		return err
	}
	defer wc.Close()

	headers := make(map[string]string)
	headers["From"] = conf.Sender
	headers["To"] = strings.Join(conf.Recipients, ",")
	headers["Subject"] = msg.Subject
	headers["MIME-Version"] = "1.0"
	headers["Content-Type"] = "text/html; charset=UTF-8"

	body := ""
	for k, v := range headers {
		body += fmt.Sprintf("%s: %s\r\n", k, v)
	}
	for _, par := range msg.Paragraphs {
		body += "<p>" + par + "</p>\r\n\r\n"
	}
	body += fmt.Sprintf("<p>Generated at %s</p>\r\n\r\n", datetime.GetCurrentDatetimeIn(location))

	buf := bytes.NewBufferString(body)
	_, err = buf.WriteTo(wc)
	return err
}