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))
}

func (app *App) resolveBaseURL() string {
	baseURL := app.baseURL
	if baseURL == "" {
		app.db.QueryRow(`SELECT value FROM config WHERE key = 'base_url'`).Scan(&baseURL)
	}
	return strings.TrimRight(baseURL, "/")
}

func (app *App) eventName() string {
	event, _ := app.getEvent()
	if event != nil && event.Name != "" {
		return event.Name
	}
	return "the event"
}

// 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()
	eventName := app.eventName()
	link := fmt.Sprintf("%s/v/%s", app.resolveBaseURL(), *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)
}

func (app *App) sendConfirmationEmail(to, name, confirmToken string) error {
	cfg := app.loadSMTPConfig()
	eventName := app.eventName()
	link := fmt.Sprintf("%s/confirm/%s", app.resolveBaseURL(), confirmToken)
	subject := fmt.Sprintf("Please confirm your email for %s", eventName)
	body := fmt.Sprintf(
		"Hi %s,\n\nThank you for signing up to volunteer at %s!\n\nPlease confirm your email address by visiting:\n%s\n\nIf you did not sign up, you can safely ignore this email.\n",
		name, eventName, link,
	)
	return sendEmail(cfg, to, subject, body)
}

func (app *App) sendShiftSignupEmail(to, name, kioskLink string) error {
	cfg := app.loadSMTPConfig()
	eventName := app.eventName()
	subject := fmt.Sprintf("Shift signups are open for %s!", eventName)
	body := fmt.Sprintf(
		"Hi %s,\n\nShift signups are now open for %s!\n\nUse this link to sign up for available shifts:\n%s\n\nSee you there!\n",
		name, eventName, kioskLink,
	)
	return sendEmail(cfg, to, subject, body)
}