school-timetracker/backend/database.go

package main

import (
	"database/sql"
	"fmt"
	"log"
	"os"
	"sort"
	"strconv"
	"strings"
	"time"

	"golang.org/x/crypto/bcrypt"
	_ "modernc.org/sqlite"
)

func InitDB(filepath string) *sql.DB {
	dsn := filepath + "?_pragma=journal_mode(WAL)&_pragma=busy_timeout(5000)&_pragma=synchronous(NORMAL)"

	db, err := sql.Open("sqlite", dsn)
	if err != nil {
		log.Fatal(err)
	}

	db.SetMaxOpenConns(1)
	db.SetMaxIdleConns(1)
	db.SetConnMaxLifetime(time.Hour)

	if err = db.Ping(); err != nil {
		log.Fatal(err)
	}

	createTables(db)
	createIndexes(db)

	ensureAdminExists(db)

	return db
}

func ensureAdminExists(db *sql.DB) {
	var count int
	db.QueryRow("SELECT COUNT(*) FROM users").Scan(&count)
	if count == 0 {
		var pw []byte
		if os.Getenv("INITIAL_ADMIN_PASSWORD") == "" {
			log.Println("Keine Benutzer gefunden. Erstelle Standard-Admin...")
			pw, _ = bcrypt.GenerateFromPassword([]byte("admin123"), bcrypt.DefaultCost)
		} else {
			initialPassword := os.Getenv("INITIAL_ADMIN_PASSWORD")
			pw, _ = bcrypt.GenerateFromPassword([]byte(initialPassword), bcrypt.DefaultCost)
		}
		_, err := db.Exec("INSERT INTO users (username, password, is_admin, yearly_hours) VALUES (?, ?, ?, ?)",
			"admin", string(pw), true, 0)
		if err != nil {
			log.Printf("Fehler beim Erstellen des Admins: %v", err)
		} else {
			log.Println("Admin erstellt. User: 'admin', Pass: 'admin123'")
		}
	}
}

func createTables(db *sql.DB) {
	queries := []string{
		`CREATE TABLE IF NOT EXISTS users (
		  id INTEGER PRIMARY KEY AUTOINCREMENT,
		  username TEXT UNIQUE NOT NULL,
		  password TEXT NOT NULL,
		  is_admin BOOLEAN NOT NULL DEFAULT 0,
		  yearly_hours REAL NOT NULL DEFAULT 60.0,
		  created_at DATETIME DEFAULT CURRENT_TIMESTAMP
		)`,
		`CREATE TABLE IF NOT EXISTS schedules (
			id INTEGER PRIMARY KEY AUTOINCREMENT,
			day_of_week INTEGER NOT NULL,
			start_time TEXT NOT NULL,
			end_time TEXT NOT NULL,
			type TEXT NOT NULL,
			title TEXT NOT NULL,
			created_at DATETIME DEFAULT CURRENT_TIMESTAMP
		)`,
		`CREATE TABLE IF NOT EXISTS time_entries (
			id INTEGER PRIMARY KEY AUTOINCREMENT,
			user_id INTEGER NOT NULL,
			schedule_id INTEGER NOT NULL,
			date TEXT NOT NULL,
			type TEXT NOT NULL,
			start_time TEXT NOT NULL,
			end_time TEXT NOT NULL,
			created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
			FOREIGN KEY(user_id) REFERENCES users(id),
			FOREIGN KEY(schedule_id) REFERENCES schedules(id)
		)`,
		`CREATE TABLE IF NOT EXISTS school_years (
			id INTEGER PRIMARY KEY AUTOINCREMENT,
			name TEXT NOT NULL,
			start_date TEXT NOT NULL,
			end_date TEXT NOT NULL,
			is_active BOOLEAN NOT NULL DEFAULT 0,
			created_at DATETIME DEFAULT CURRENT_TIMESTAMP
		)`,
		`CREATE TABLE IF NOT EXISTS substitutions (
			id INTEGER PRIMARY KEY AUTOINCREMENT,
			date TEXT NOT NULL,
			start_time TEXT NOT NULL,
			end_time TEXT NOT NULL,
			title TEXT NOT NULL,
			notes TEXT,
			taken_by_user_id INTEGER,
			schedule_id INTEGER NOT NULL,
			created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
			FOREIGN KEY(taken_by_user_id) REFERENCES users(id),
			FOREIGN KEY(schedule_id) REFERENCES schedules(id)
		)`,
	}

	for _, query := range queries {
		_, err := db.Exec(query)
		if err != nil {
			log.Fatalf("Error creating table: %s\nQuery: %s", err, query)
		}
	}
}

func createIndexes(db *sql.DB) {
	indexes := []string{
		"CREATE UNIQUE INDEX IF NOT EXISTS idx_users_username ON users(username)",
		"CREATE INDEX IF NOT EXISTS idx_time_entries_user_date ON time_entries(user_id, date)",
		"CREATE INDEX IF NOT EXISTS idx_schedules_day ON schedules(day_of_week)",
		`CREATE INDEX IF NOT EXISTS idx_substitutions_date ON substitutions(date)`,
	}
	for _, idx := range indexes {
		db.Exec(idx)
	}
}

func GetUserByUsername(db *sql.DB, username string) (*User, error) {
	user := &User{}
	err := db.QueryRow("SELECT id, username, password, is_admin, yearly_hours FROM users WHERE username = ?", username).
		Scan(&user.ID, &user.Username, &user.Password, &user.IsAdmin, &user.YearlyHours)
	if err != nil {
		return nil, err
	}
	return user, nil
}

func GetUserByID(db *sql.DB, userID int) (*User, error) {
	user := &User{}
	err := db.QueryRow("SELECT id, username, password, is_admin, yearly_hours FROM users WHERE id = ?", userID).
		Scan(&user.ID, &user.Username, &user.Password, &user.IsAdmin, &user.YearlyHours)
	if err != nil {
		return nil, err
	}
	return user, nil
}

func CreateUser(db *sql.DB, username, hashedPassword string, isAdmin bool, yearlyHours float64) error {
	_, err := db.Exec("INSERT INTO users (username, password, is_admin, yearly_hours) VALUES (?, ?, ?, ?)",
		username, hashedPassword, isAdmin, yearlyHours)
	return err
}

func GetAllUsers(db *sql.DB) ([]User, error) {
	rows, err := db.Query("SELECT id, username, is_admin, yearly_hours FROM users ORDER BY username")
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var users []User
	for rows.Next() {
		var u User
		if err := rows.Scan(&u.ID, &u.Username, &u.IsAdmin, &u.YearlyHours); err != nil {
			continue
		}
		users = append(users, u)
	}
	return users, nil
}

func UpdateUser(db *sql.DB, userID int, yearlyHours float64) error {
	_, err := db.Exec("UPDATE users SET yearly_hours = ? WHERE id = ?",
		yearlyHours, userID)
	return err
}

func ResetUserPassword(db *sql.DB, userID int, hashedPassword string) error {
	_, err := db.Exec("UPDATE users SET password = ? WHERE id = ?", hashedPassword, userID)
	return err
}

func DeleteUser(db *sql.DB, id int) error {
	if id == 1 {
		return fmt.Errorf("cannot delete admin user")
	}
	_, err := db.Exec("DELETE FROM users WHERE id = ?", id)
	return err
}

func CreateSchedule(db *sql.DB, schedule *Schedule) error {
	_, err := db.Exec("INSERT INTO schedules (day_of_week, start_time, end_time, type, title) VALUES (?, ?, ?, ?, ?)",
		schedule.DayOfWeek, schedule.StartTime, schedule.EndTime, schedule.Type, schedule.Title)
	return err
}

func GetAllSchedules(db *sql.DB) ([]Schedule, error) {
	rows, err := db.Query("SELECT id, day_of_week, start_time, end_time, type, title FROM schedules ORDER BY day_of_week, start_time")
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var schedules []Schedule
	for rows.Next() {
		var s Schedule
		if err := rows.Scan(&s.ID, &s.DayOfWeek, &s.StartTime, &s.EndTime, &s.Type, &s.Title); err != nil {
			continue
		}
		schedules = append(schedules, s)
	}
	return schedules, nil
}

func DeleteSchedule(db *sql.DB, id int) error {
	_, err := db.Exec("DELETE FROM schedules WHERE id = ?", id)
	return err
}

func UpdateTimeEntry(db *sql.DB, entryID int, date, startTime, endTime, entryType string) error {
	_, err := db.Exec("UPDATE time_entries SET date = ?, start_time = ?, end_time = ?, type = ? WHERE id = ?",
		date, startTime, endTime, entryType, entryID)
	return err
}

func DeleteTimeEntry(db *sql.DB, entryID int) error {
	_, err := db.Exec("DELETE FROM time_entries WHERE id = ?", entryID)
	return err
}

func CreateTimeEntry(db *sql.DB, entry *TimeEntry) error {
	_, err := db.Exec("INSERT INTO time_entries (user_id, schedule_id, date, type, start_time, end_time) VALUES (?, ?, ?, ?, ?, ?)",
		entry.UserID, entry.ScheduleID, entry.Date, entry.Type, entry.StartTime, entry.EndTime)
	return err
}

func GetTimeEntriesByUser(db *sql.DB, userID int) ([]TimeEntry, error) {
	rows, err := db.Query(`
        SELECT te.id, te.user_id, te.schedule_id, te.date, te.type, te.start_time, te.end_time, te.created_at, u.username
        FROM time_entries te
        JOIN users u ON te.user_id = u.id
        WHERE te.user_id = ?
        ORDER BY te.date DESC, te.created_at DESC
    `, userID)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var entries []TimeEntry
	for rows.Next() {
		var e TimeEntry
		if err := rows.Scan(&e.ID, &e.UserID, &e.ScheduleID, &e.Date, &e.Type, &e.StartTime, &e.EndTime, &e.CreatedAt, &e.Username); err != nil {
			continue
		}
		entries = append(entries, e)
	}
	return entries, nil
}

func GetAllTimeEntries(db *sql.DB) ([]TimeEntry, error) {
	rows, err := db.Query(`
        SELECT te.id, te.user_id, te.schedule_id, te.date, te.type, te.start_time, te.end_time, te.created_at, u.username
        FROM time_entries te
        JOIN users u ON te.user_id = u.id
        ORDER BY te.date DESC, te.created_at DESC
    `)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var entries []TimeEntry
	for rows.Next() {
		var e TimeEntry
		if err := rows.Scan(&e.ID, &e.UserID, &e.ScheduleID, &e.Date, &e.Type, &e.StartTime, &e.EndTime, &e.CreatedAt, &e.Username); err != nil {
			continue
		}
		entries = append(entries, e)
	}
	return entries, nil
}

func GetWeeklyHours(db *sql.DB) ([]WeeklyHours, error) {
	rows, err := db.Query(`
        SELECT
            te.user_id,
            u.username,
            te.date,
            te.start_time,
            te.end_time,
            te.type,
            u.yearly_hours
        FROM time_entries te
        JOIN users u ON te.user_id = u.id
        ORDER BY te.date DESC
    `)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	hoursMap := make(map[string]*WeeklyHours)
	userYearlyHours := make(map[int]float64)

	for rows.Next() {
		var userID int
		var username, dateStr, startTime, endTime, entryType string
		var yearlyHours float64

		if err := rows.Scan(&userID, &username, &dateStr, &startTime, &endTime, &entryType, &yearlyHours); err != nil {
			continue
		}

		userYearlyHours[userID] = yearlyHours

		t, err := time.Parse("2006-01-02", dateStr)
		if err != nil {
			continue
		}

		year, week := t.ISOWeek()

		entry := TimeEntry{
			Type:      entryType,
			StartTime: startTime,
			EndTime:   endTime,
		}
		hours := calculateHours(entry)

		key := fmt.Sprintf("%d_%d_%d", userID, year, week)
		if existing, exists := hoursMap[key]; exists {
			existing.TotalHours += hours
		} else {
			hoursMap[key] = &WeeklyHours{
				UserID:     userID,
				Username:   username,
				Year:       year,
				Week:       week,
				TotalHours: hours,
			}
		}
	}

	yearlyTotals := make(map[int]float64)
	for _, h := range hoursMap {
		yearlyTotals[h.UserID] += h.TotalHours
	}

	for _, h := range hoursMap {
		h.YearlyTarget = userYearlyHours[h.UserID]
		h.YearlyActual = yearlyTotals[h.UserID]

		h.WeeklyTarget = h.YearlyTarget / 45.0
		h.RemainingYearly = h.YearlyTarget - h.YearlyActual
	}

	var result []WeeklyHours
	for _, h := range hoursMap {
		result = append(result, *h)
	}

	sort.Slice(result, func(i, j int) bool {
		if result[i].Year != result[j].Year {
			return result[i].Year > result[j].Year
		}
		if result[i].Week != result[j].Week {
			return result[i].Week > result[j].Week
		}
		return result[i].Username < result[j].Username
	})

	return result, nil
}

func calculateHoursDiff(startTime, endTime string) float64 {
	parseTime := func(timeStr string) float64 {
		parts := strings.Split(timeStr, ":")
		if len(parts) != 2 {
			return 0
		}

		hours, err1 := strconv.ParseFloat(parts[0], 64)
		minutes, err2 := strconv.ParseFloat(parts[1], 64)

		if err1 != nil || err2 != nil {
			return 0
		}

		return hours + (minutes / 60.0)
	}

	start := parseTime(startTime)
	end := parseTime(endTime)

	if end > start {
		return end - start
	}
	return 0
}

func DeleteTimeEntriesByUserAndWeek(db *sql.DB, userID int, year int, week int) error {
	dates := calculateWeekDates(year, week)

	var dateList []string
	for day := 0; day <= 4; day++ {
		dateList = append(dateList, dates.Dates[fmt.Sprintf("%d", day)])
	}

	query := `
        DELETE FROM time_entries
        WHERE user_id = ?
        AND date IN (?, ?, ?, ?, ?)
    `
	_, err := db.Exec(query, userID, dateList[0], dateList[1], dateList[2], dateList[3], dateList[4])
	return err
}

func CheckUserHasEntriesForWeek(db *sql.DB, userID int, year int, week int) (bool, error) {
	dates := calculateWeekDates(year, week)

	var dateList []string
	for day := 0; day <= 4; day++ {
		dateList = append(dateList, dates.Dates[fmt.Sprintf("%d", day)])
	}

	query := `
        SELECT COUNT(*)
        FROM time_entries
        WHERE user_id = ?
        AND date IN (?, ?, ?, ?, ?)
    `

	var count int
	err := db.QueryRow(query, userID,
		dateList[0], dateList[1], dateList[2], dateList[3], dateList[4]).Scan(&count)
	if err != nil {
		log.Printf("Error checking entries: %v", err)
		return false, err
	}

	return count > 0, nil
}

func GetActiveSchoolYear(db *sql.DB) (*SchoolYear, error) {
	var sy SchoolYear
	err := db.QueryRow(`
        SELECT id, name, start_date, end_date, is_active, created_at
        FROM school_years
        WHERE is_active = 1
    `).Scan(&sy.ID, &sy.Name, &sy.StartDate, &sy.EndDate, &sy.IsActive, &sy.CreatedAt)

	if err == sql.ErrNoRows {
		return nil, nil
	}
	return &sy, err
}

func GetAllSchoolYears(db *sql.DB) ([]SchoolYear, error) {
	rows, err := db.Query(`
        SELECT id, name, start_date, end_date, is_active, created_at
        FROM school_years
        ORDER BY start_date DESC
    `)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	years := []SchoolYear{}
	for rows.Next() {
		var sy SchoolYear
		if err := rows.Scan(&sy.ID, &sy.Name, &sy.StartDate, &sy.EndDate, &sy.IsActive, &sy.CreatedAt); err != nil {
			continue
		}
		years = append(years, sy)
	}
	return years, rows.Err()
}

func CreateSchoolYear(db *sql.DB, name, startDate, endDate string) error {
	_, err := db.Exec(`
        INSERT INTO school_years (name, start_date, end_date, is_active)
        VALUES (?, ?, ?, 0)
    `, name, startDate, endDate)
	return err
}

func SetActiveSchoolYear(db *sql.DB, id int) error {
	tx, err := db.Begin()
	if err != nil {
		return err
	}

	if _, err := tx.Exec("UPDATE school_years SET is_active = 0"); err != nil {
		tx.Rollback()
		return err
	}

	if _, err := tx.Exec("UPDATE school_years SET is_active = 1 WHERE id = ?", id); err != nil {
		tx.Rollback()
		return err
	}

	return tx.Commit()
}

func GetYearlyHoursSummary(db *sql.DB) ([]WeeklyHours, error) {
	schoolYear, err := GetActiveSchoolYear(db)
	if err != nil || schoolYear == nil {
		return []WeeklyHours{}, err
	}

	users, err := GetAllUsers(db)
	if err != nil {
		return []WeeklyHours{}, err
	}

	rows, err := db.Query(`
        SELECT user_id, date, start_time, end_time, type
        FROM time_entries
        WHERE date >= ? AND date <= ?
        ORDER BY date DESC
    `, schoolYear.StartDate, schoolYear.EndDate)
	if err != nil {
		return []WeeklyHours{}, err
	}
	defer rows.Close()

	userTotals := make(map[int]float64)

	for rows.Next() {
		var userID int
		var date, startTime, endTime, entryType string

		if err := rows.Scan(&userID, &date, &startTime, &endTime, &entryType); err != nil {
			continue
		}

		entry := TimeEntry{
			Type:      entryType,
			StartTime: startTime,
			EndTime:   endTime,
		}
		hours := calculateHours(entry)
		userTotals[userID] += hours
	}

	var result []WeeklyHours
	for _, user := range users {
		if !user.IsAdmin {
			total := userTotals[user.ID]
			remaining := user.YearlyHours - total

			result = append(result, WeeklyHours{
				UserID:          user.ID,
				Username:        user.Username,
				Year:            0,
				Week:            0,
				TotalHours:      total,
				YearlyTarget:    user.YearlyHours,
				YearlyActual:    total,
				RemainingYearly: remaining,
			})
		}
	}

	return result, nil
}

func CreateManualTimeEntry(db *sql.DB, entry *TimeEntry, hours float64) error {
	entry.StartTime = fmt.Sprintf("%.2f", hours)
	entry.EndTime = "manual"
	entry.Type = "manual"

	_, err := db.Exec(`
        INSERT INTO time_entries (user_id, schedule_id, date, type, start_time, end_time)
        VALUES (?, 0, ?, ?, ?, ?)
    `, entry.UserID, entry.Date, entry.Type, entry.StartTime, entry.EndTime)

	return err
}

func calculateHours(entry TimeEntry) float64 {
	switch entry.Type {
	case "lesson":
		return 1.0
	case "manual":
		hours, err := strconv.ParseFloat(entry.StartTime, 64)
		if err != nil {
			return 0
		}
		return hours
	default:
		return calculateHoursDiff(entry.StartTime, entry.EndTime)
	}
}

func DeleteSchoolYear(db *sql.DB, id int) error {
	var isActive bool
	err := db.QueryRow("SELECT is_active FROM school_years WHERE id = ?", id).Scan(&isActive)
	if err != nil {
		return err
	}

	if isActive {
		return fmt.Errorf("cannot delete active school year")
	}

	result, err := db.Exec("DELETE FROM school_years WHERE id = ? AND is_active = 0", id)
	if err != nil {
		return err
	}

	rowsAffected, err := result.RowsAffected()
	if err != nil {
		return err
	}

	if rowsAffected == 0 {
		return sql.ErrNoRows
	}

	return nil
}

func DeleteNonManualTimeEntriesByUserAndWeek(db *sql.DB, userID int, year int, week int) error {
	dates := calculateWeekDates(year, week)
	var dateList []string
	for day := 0; day <= 4; day++ {
		dateList = append(dateList, dates.Dates[fmt.Sprint(day)])
	}
	tx, err := db.Begin()
	if err != nil {
		return err
	}
	defer tx.Rollback()

	_, err = tx.Exec(`
		UPDATE substitutions 
		SET taken_by_user_id = NULL 
		WHERE taken_by_user_id = ? 
		AND date IN (?, ?, ?, ?, ?)
	`, userID, dateList[0], dateList[1], dateList[2], dateList[3], dateList[4])
	if err != nil {
		return err
	}

	query := `DELETE FROM time_entries 
	          WHERE user_id = ? 
	          AND type != 'manual' 
	          AND date IN (?, ?, ?, ?, ?)`

	_, err = tx.Exec(query, userID, dateList[0], dateList[1], dateList[2], dateList[3], dateList[4])
	if err != nil {
		return err
	}

	return tx.Commit()
}

func CreateSubstitution(db *sql.DB, date, start, end, title, notes string, scheduleID int) error {
	_, err := db.Exec(`
		INSERT INTO substitutions (date, start_time, end_time, title, notes, schedule_id)
		VALUES (?, ?, ?, ?, ?, ?)
	`, date, start, end, title, notes, scheduleID)
	return err
}

func GetOpenSubstitutions(db *sql.DB) ([]Substitution, error) {
	today := time.Now().Format("2006-01-02")

	rows, err := db.Query(`
		SELECT id, date, start_time, end_time, title, notes, schedule_id, created_at
		FROM substitutions
		WHERE taken_by_user_id IS NULL
		AND date >= ? 
		ORDER BY date ASC, start_time ASC
	`, today)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var subs []Substitution
	for rows.Next() {
		var s Substitution
		if err := rows.Scan(&s.ID, &s.Date, &s.StartTime, &s.EndTime, &s.Title, &s.Notes, &s.ScheduleID, &s.CreatedAt); err != nil {
			continue
		}
		subs = append(subs, s)
	}
	return subs, nil
}

func GetAllSubstitutions(db *sql.DB) ([]Substitution, error) {
	rows, err := db.Query(`
		SELECT 
			s.id, 
			s.date, 
			s.start_time, 
			s.end_time, 
			s.title, 
			s.notes, 
			s.schedule_id,
			s.created_at,
			s.taken_by_user_id, 
			u.username
		FROM substitutions s
		LEFT JOIN users u ON s.taken_by_user_id = u.id
		ORDER BY s.date DESC
	`)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var subs []Substitution
	for rows.Next() {
		var s Substitution

		var takenID sql.NullInt64
		var takenName sql.NullString

		if err := rows.Scan(
			&s.ID,
			&s.Date,
			&s.StartTime,
			&s.EndTime,
			&s.Title,
			&s.Notes,
			&s.ScheduleID,
			&s.CreatedAt,
			&takenID,
			&takenName,
		); err != nil {
			continue
		}

		if takenID.Valid {
			id := int(takenID.Int64)
			s.TakenByUserID = &id
			s.TakenByUsername = takenName.String
		}

		subs = append(subs, s)
	}
	return subs, nil
}

func DeleteSubstitution(db *sql.DB, id int) error {
	tx, err := db.Begin()
	if err != nil {
		return err
	}
	defer tx.Rollback()

	var takenByUserID sql.NullInt64
	var scheduleID int
	var date string

	err = tx.QueryRow(`
		SELECT taken_by_user_id, schedule_id, date 
		FROM substitutions 
		WHERE id = ?
	`, id).Scan(&takenByUserID, &scheduleID, &date)
	if err != nil {
		if err == sql.ErrNoRows {
			return nil
		}
		return err
	}

	if takenByUserID.Valid {
		userID := int(takenByUserID.Int64)

		_, err = tx.Exec(`
			DELETE FROM time_entries 
			WHERE user_id = ? AND schedule_id = ? AND date = ?
		`, userID, scheduleID, date)
		if err != nil {
			return err
		}
	}

	_, err = tx.Exec("DELETE FROM substitutions WHERE id = ?", id)
	if err != nil {
		return err
	}

	return tx.Commit()
}

func AcceptSubstitution(db *sql.DB, substitutionID int, userID int) error {
	tx, err := db.Begin()
	if err != nil {
		return err
	}
	defer tx.Rollback()

	var currentDate, start, end string
	var scheduleID int
	var scheduleType string

	err = tx.QueryRow(`
		SELECT s.date, s.start_time, s.end_time, s.schedule_id, sch.type
		FROM substitutions s
		JOIN schedules sch ON s.schedule_id = sch.id
		WHERE s.id = ? AND s.taken_by_user_id IS NULL
	`, substitutionID).Scan(&currentDate, &start, &end, &scheduleID, &scheduleType)

	if err == sql.ErrNoRows {
		return fmt.Errorf("Vertretung wurde bereits vergeben oder existiert nicht")
	}
	if err != nil {
		return err
	}

	_, err = tx.Exec(`UPDATE substitutions SET taken_by_user_id = ? WHERE id = ?`, userID, substitutionID)
	if err != nil {
		return err
	}

	_, err = tx.Exec(`
		INSERT INTO time_entries (user_id, schedule_id, date, type, start_time, end_time)
		VALUES (?, ?, ?, ?, ?, ?)
	`, userID, scheduleID, currentDate, scheduleType, start, end)
	if err != nil {
		return err
	}

	return tx.Commit()
}