feat: attach iCalendar (.ics) file to confirmation email

main.go

@@ -10,6 +10,7 @@ import (
 	"net/smtp"
 	"os"
 	"strings"
+	"time"
 )
 
 type Activity struct {
@@ -131,12 +132,19 @@ func sendEmail(payload SurveyPayload) error {
 		return nil
 	}
 
+	boundary := fmt.Sprintf("BOUNDARY_%d", time.Now().UnixNano())
+
 	var bodyBuilder bytes.Buffer
 	bodyBuilder.WriteString(fmt.Sprintf("From: %s\r\n", fromEmail))
 	bodyBuilder.WriteString(fmt.Sprintf("To: %s\r\n", toEmail))
 	bodyBuilder.WriteString(fmt.Sprintf("Subject: Neue Date-Reservierung von %s! 💕\r\n", payload.Name))
 	bodyBuilder.WriteString("MIME-Version: 1.0\r\n")
-	bodyBuilder.WriteString("Content-Type: text/plain; charset=UTF-8\r\n\r\n")
+	bodyBuilder.WriteString(fmt.Sprintf("Content-Type: multipart/mixed; boundary=\"%s\"\r\n\r\n", boundary))
+
+	// Text-Teil der E-Mail
+	bodyBuilder.WriteString(fmt.Sprintf("--%s\r\n", boundary))
+	bodyBuilder.WriteString("Content-Type: text/plain; charset=UTF-8\r\n")
+	bodyBuilder.WriteString("Content-Transfer-Encoding: 8bit\r\n\r\n")
 
 	bodyBuilder.WriteString("Hallo!\r\n\r\n")
 	bodyBuilder.WriteString("Es gibt eine neue Date-Reservierung über deinen Date-Planer:\r\n\r\n")
@@ -152,7 +160,19 @@ func sendEmail(payload SurveyPayload) error {
 		bodyBuilder.WriteString("\r\n")
 	}
 
-	bodyBuilder.WriteString("Viel Spaß beim gemeinsamen Date! 💕\r\n")
+	bodyBuilder.WriteString("Im Anhang findest du einen Kalendereintrag (.ics), den du direkt auf deinem Smartphone/Kalender importieren kannst. 💕\r\n\r\n")
+
+	// iCalendar-Anhang (.ics)
+	icsData := generateICS(payload)
+	bodyBuilder.WriteString(fmt.Sprintf("--%s\r\n", boundary))
+	bodyBuilder.WriteString("Content-Type: text/calendar; charset=UTF-8; method=REQUEST; name=\"date-event.ics\"\r\n")
+	bodyBuilder.WriteString("Content-Disposition: attachment; filename=\"date-event.ics\"\r\n")
+	bodyBuilder.WriteString("Content-Transfer-Encoding: 8bit\r\n\r\n")
+	bodyBuilder.WriteString(icsData)
+	bodyBuilder.WriteString("\r\n")
+
+	// Abschluss-Boundary
+	bodyBuilder.WriteString(fmt.Sprintf("--%s--\r\n", boundary))
 
 	auth := smtp.PlainAuth("", smtpUser, smtpPass, smtpHost)
 	addr := fmt.Sprintf("%s:%s", smtpHost, smtpPort)
@@ -160,6 +180,41 @@ func sendEmail(payload SurveyPayload) error {
 	return smtp.SendMail(addr, auth, fromEmail, []string{toEmail}, bodyBuilder.Bytes())
 }
 
+func generateICS(payload SurveyPayload) string {
+	parsedDate, err := time.Parse("2006-01-02", payload.Date)
+	dtStart := strings.ReplaceAll(payload.Date, "-", "")
+	dtEnd := dtStart
+	if err == nil {
+		dtStart = parsedDate.Format("20060102")
+		dtEnd = parsedDate.AddDate(0, 0, 1).Format("20060102")
+	}
+
+	dtStamp := time.Now().UTC().Format("20060102T150405Z")
+	uid := fmt.Sprintf("date-wizard-%s-%d@date-wizard", dtStart, time.Now().UnixNano())
+
+	summary := fmt.Sprintf("Date: %s", payload.Activity)
+	description := fmt.Sprintf("Date mit %s\\nAktivität(en): %s", payload.Name, payload.Activity)
+
+	var sb strings.Builder
+	sb.WriteString("BEGIN:VCALENDAR\r\n")
+	sb.WriteString("VERSION:2.0\r\n")
+	sb.WriteString("PRODID:-//Date-Wizard//DE\r\n")
+	sb.WriteString("CALSCALE:GREGORIAN\r\n")
+	sb.WriteString("METHOD:REQUEST\r\n")
+	sb.WriteString("BEGIN:VEVENT\r\n")
+	sb.WriteString(fmt.Sprintf("UID:%s\r\n", uid))
+	sb.WriteString(fmt.Sprintf("DTSTAMP:%s\r\n", dtStamp))
+	sb.WriteString(fmt.Sprintf("DTSTART;VALUE=DATE:%s\r\n", dtStart))
+	sb.WriteString(fmt.Sprintf("DTEND;VALUE=DATE:%s\r\n", dtEnd))
+	sb.WriteString(fmt.Sprintf("SUMMARY:%s\r\n", summary))
+	sb.WriteString(fmt.Sprintf("DESCRIPTION:%s\r\n", description))
+	sb.WriteString("STATUS:CONFIRMED\r\n")
+	sb.WriteString("END:VEVENT\r\n")
+	sb.WriteString("END:VCALENDAR\r\n")
+
+	return sb.String()
+}
+
 func loadEnv(filename string) {
 	file, err := os.Open(filename)
 	if err != nil {