sprechstunden-go/repositories/request.go

// request
package repositories

import (
	"bytes"
	"crypto/rand"
	"database/sql"
	"html/template"
	"math/big"
	"net/smtp"
	"sprechstundentool/models"
)

type RequestRepo struct {
	db             *sql.DB
	officeHourRepo models.OfficeHourRepository
}

func NewRequestRepo(db *sql.DB, officeHourRepo models.OfficeHourRepository) *RequestRepo {
	return &RequestRepo{
		db:             db,
		officeHourRepo: officeHourRepo,
	}
}

func (r *RequestRepo) FindBySecret(secret string) (models.Request, error) {
	// This query is not safe against timing sidechannel attacks – I don't care.
	row := r.db.QueryRow("SELECT * FROM request WHERE secret=?", secret)
	var request models.Request
	var officeHourId int
	err := row.Scan(&request.Id, &officeHourId, &request.Action, &request.Secret)
	if err != nil {
		return models.Request{}, err
	}
	request.OfficeHour, err = r.officeHourRepo.FindById(officeHourId)
	return request, err
}

func (r *RequestRepo) FindByOfficeHour(officeHour models.OfficeHour) ([]models.Request, error) {
	rows, err := r.db.Query("SELECT * FROM request WHERE officeHour=?", officeHour.Id)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var requests []models.Request
	for rows.Next() {
		var request models.Request
		var officeHourId int
		if err := rows.Scan(&request.Id, &officeHourId, &request.Action, &request.Secret); err != nil {
			return requests, err
		}
		requests = append(requests, request)
	}
	return requests, nil
}

func (r *RequestRepo) Add(officeHour models.OfficeHour, action int) (int, error) {
	existents, err := r.FindByOfficeHour(officeHour)
	if err != nil && err != sql.ErrNoRows {
		return 0, err
	}
	/* Resend confirmation mail if identical request exists,
	 * but don't insert new request into database.
	 */
	for _, request := range existents {
		if request.Action == action { // already covered by selection && request.OfficeHour == officeHour {
			return request.Id, sendConfirmationMail(request)
		}
	}
	secret, err := r.newSecret()
	if err != nil {
		return 0, err
	}
	request := models.Request{0, officeHour, action, secret}
	_, err = r.db.Exec("INSERT INTO `request` (officeHour, action, secret) VALUES (?,?,?)", officeHour.Id, action, secret)
	if err != nil {
		return 0, err
	}

	request, err = r.FindBySecret(secret)
	if err != nil {
		return request.Id, err
	}
	return request.Id, sendConfirmationMail(request)
}

func (r *RequestRepo) Execute(request models.Request) error {
	var err error
	switch request.Action {
	case models.RequestActivate:
		_, err = r.db.Exec("UPDATE officeHour SET active=true WHERE id=?", request.OfficeHour.Id)
		r.db.Exec("DELETE FROM request WHERE id=?", request.Id)
	case models.RequestDelete:
		_, err = r.db.Exec("DELETE FROM officeHour WHERE id=?", request.OfficeHour.Id)
		r.db.Exec("DELETE FROM request WHERE id=?", request.Id)
	default:
		r.db.Exec("DELETE FROM request WHERE id=?", request.Id)
	}
	return err
}

func (r *RequestRepo) newSecret() (string, error) {
	secret := randomString(models.SecretLength)

	_, err := r.FindBySecret(secret)
	if err != nil && err != sql.ErrNoRows {
		return "", err
	}
	// find unused secret
	for err != sql.ErrNoRows {
		secret = randomString(models.SecretLength)
		_, err = r.FindBySecret(secret)
	}
	return secret, nil
}

func sendConfirmationMail(request models.Request) error {
	to := []string{request.OfficeHour.Tutor.Email}
	tmpl, err := template.New("confirmationMail").Funcs(template.FuncMap{"DayName": models.DayName}).ParseFiles("templates/confirmationMail")
	var message bytes.Buffer
	err = tmpl.Execute(&message, request)
	if err != nil {
		return err
	}
	err = smtp.SendMail("192.168.0.24:25", nil, "Mathebau Sprechstunden <sprechstunden@mathebau.de>", to, message.Bytes())
	return err
}

func randomString(n int) string {
	// []byte would be faster and also work, but []rune keeps working for UTF8 characters
	// if someone would like them.
	var letters = []rune("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789")

	s := make([]rune, n)
	for i := range s {
		position, _ := rand.Int(rand.Reader, big.NewInt(int64(len(letters))))
		s[i] = letters[position.Int64()]
	}
	return string(s)
}