Created Turnpike, event attendee and volunteer management

Built after prototype, Traverse, an attendee and volunteer list
maintainer.

email.go

@@ -0,0 +1,140 @@
+package main
+
+import (
+	"crypto/tls"
+	"fmt"
+	"net/smtp"
+	"strings"
+)
+
+type SMTPConfig struct {
+	Host     string
+	Port     int
+	User     string
+	Password string
+	From     string
+	FromName string
+}
+
+// loadSMTPConfig reads SMTP settings from the config table, overlaying any
+// values set via CLI flags (which take priority).
+func (app *App) loadSMTPConfig() SMTPConfig {
+	get := func(key string) string {
+		var v string
+		app.db.QueryRow(`SELECT value FROM config WHERE key = ?`, key).Scan(&v)
+		return v
+	}
+
+	cfg := SMTPConfig{
+		Host:     app.smtpHost,
+		Port:     app.smtpPort,
+		User:     app.smtpUser,
+		Password: app.smtpPassword,
+		From:     app.smtpFrom,
+		FromName: app.smtpFromName,
+	}
+
+	if cfg.Host == "" {
+		cfg.Host = get("smtp_host")
+	}
+	if cfg.Port == 0 {
+		fmt.Sscanf(get("smtp_port"), "%d", &cfg.Port)
+	}
+	if cfg.User == "" {
+		cfg.User = get("smtp_user")
+	}
+	if cfg.Password == "" {
+		cfg.Password = get("smtp_password")
+	}
+	if cfg.From == "" {
+		cfg.From = get("smtp_from")
+	}
+	if cfg.FromName == "" {
+		cfg.FromName = get("smtp_from_name")
+	}
+	if cfg.Port == 0 {
+		cfg.Port = 587
+	}
+	return cfg
+}
+
+// sendEmail delivers a plain-text email.
+// Uses implicit TLS on port 465, STARTTLS on all other ports.
+func sendEmail(cfg SMTPConfig, to, subject, body string) error {
+	fromHeader := cfg.From
+	if cfg.FromName != "" {
+		fromHeader = fmt.Sprintf("%s <%s>", cfg.FromName, cfg.From)
+	}
+	msg := fmt.Sprintf(
+		"From: %s\r\nTo: %s\r\nSubject: %s\r\nMIME-Version: 1.0\r\nContent-Type: text/plain; charset=UTF-8\r\n\r\n%s",
+		fromHeader, to, subject, body,
+	)
+
+	addr := fmt.Sprintf("%s:%d", cfg.Host, cfg.Port)
+	auth := smtp.PlainAuth("", cfg.User, cfg.Password, cfg.Host)
+
+	if cfg.Port == 465 {
+		tlsCfg := &tls.Config{ServerName: cfg.Host}
+		conn, err := tls.Dial("tcp", addr, tlsCfg)
+		if err != nil {
+			return fmt.Errorf("tls dial: %w", err)
+		}
+		c, err := smtp.NewClient(conn, cfg.Host)
+		if err != nil {
+			return fmt.Errorf("smtp client: %w", err)
+		}
+		defer c.Close()
+		if err = c.Auth(auth); err != nil {
+			return fmt.Errorf("smtp auth: %w", err)
+		}
+		if err = c.Mail(cfg.From); err != nil {
+			return fmt.Errorf("smtp mail from: %w", err)
+		}
+		if err = c.Rcpt(to); err != nil {
+			return fmt.Errorf("smtp rcpt: %w", err)
+		}
+		w, err := c.Data()
+		if err != nil {
+			return fmt.Errorf("smtp data: %w", err)
+		}
+		if _, err = fmt.Fprint(w, msg); err != nil {
+			return err
+		}
+		return w.Close()
+	}
+
+	return smtp.SendMail(addr, auth, cfg.From, []string{to}, []byte(msg))
+}
+
+// sendTokenEmail sends a volunteer token link to the attendee's email address.
+func (app *App) sendTokenEmail(a Attendee) error {
+	if a.Email == "" {
+		return fmt.Errorf("attendee has no email address")
+	}
+	if a.VolunteerToken == nil || *a.VolunteerToken == "" {
+		return fmt.Errorf("attendee has no volunteer token")
+	}
+
+	cfg := app.loadSMTPConfig()
+
+	baseURL := app.baseURL
+	if baseURL == "" {
+		app.db.QueryRow(`SELECT value FROM config WHERE key = 'base_url'`).Scan(&baseURL)
+	}
+	baseURL = strings.TrimRight(baseURL, "/")
+
+	event, _ := app.getEvent()
+	eventName := "the event"
+	if event != nil && event.Name != "" {
+		eventName = event.Name
+	}
+
+	link := fmt.Sprintf("%s/#/v/%s", baseURL, *a.VolunteerToken)
+	subject := fmt.Sprintf("Your volunteer link for %s", eventName)
+	body := fmt.Sprintf(
+		"Hi %s,\n\nThank you for volunteering at %s!\n\nYour volunteer token: %s\nYour signup link: %s\n\nUse this link to sign up for available shifts in your department.\n\nSee you there!\n",
+		a.Name, eventName, *a.VolunteerToken, link,
+	)
+
+	return sendEmail(cfg, a.Email, subject, body)
+}