Add notifications package for easy sending of notifications (#779)

Co-authored-by: kolaente <k@knt.li>
Reviewed-on: https://kolaente.dev/vikunja/api/pulls/779
Co-authored-by: konrad <konrad@kola-entertainments.de>
Co-committed-by: konrad <konrad@kola-entertainments.de>

pkg/notifications/mail.go

@@ -0,0 +1,93 @@
+// Vikunja is a to-do list application to facilitate your life.
+// Copyright 2018-2021 Vikunja and contributors. All rights reserved.
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public Licensee as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public Licensee for more details.
+//
+// You should have received a copy of the GNU Affero General Public Licensee
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package notifications
+
+import "code.vikunja.io/api/pkg/mail"
+
+// Mail is a mail message
+type Mail struct {
+	from       string
+	to         string
+	subject    string
+	actionText string
+	actionURL  string
+	greeting   string
+	introLines []string
+	outroLines []string
+}
+
+// NewMail creates a new mail object with a default greeting
+func NewMail() *Mail {
+	return &Mail{
+		greeting: "Hi,",
+	}
+}
+
+// From sets the from name and email address
+func (m *Mail) From(from string) *Mail {
+	m.from = from
+	return m
+}
+
+// To sets the recipient of the mail message
+func (m *Mail) To(to string) *Mail {
+	m.to = to
+	return m
+}
+
+// Subject sets the subject of the mail message
+func (m *Mail) Subject(subject string) *Mail {
+	m.subject = subject
+	return m
+}
+
+// Greeting sets the greeting of the mail message
+func (m *Mail) Greeting(greeting string) *Mail {
+	m.greeting = greeting
+	return m
+}
+
+// Action sets any action a mail might have
+func (m *Mail) Action(text, url string) *Mail {
+	m.actionText = text
+	m.actionURL = url
+	return m
+}
+
+// Line adds a line of text to the mail
+func (m *Mail) Line(line string) *Mail {
+	if m.actionURL == "" {
+		m.introLines = append(m.introLines, line)
+		return m
+	}
+
+	m.outroLines = append(m.outroLines, line)
+
+	return m
+}
+
+// SendMail passes the notification to the mailing queue for sending
+func SendMail(m *Mail) error {
+	opts, err := RenderMail(m)
+	if err != nil {
+		return err
+	}
+
+	mail.SendMail(opts)
+
+	return nil
+}