@RequestMapping(value = "/events/{eventName}/categories-containing-tickets", method = GET)
 public List<TicketCategoryModification> getCategoriesWithTickets(
     @PathVariable("eventName") String eventName, Principal principal) {
   Event event = loadEvent(eventName, principal);
   return eventStatisticsManager
       .loadTicketCategoriesWithStats(event)
       .stream()
       .filter(tc -> !tc.getTickets().isEmpty())
       .map(
           tc ->
               TicketCategoryModification.fromTicketCategory(
                   tc.getTicketCategory(),
                   ticketCategoryDescriptionRepository.findByTicketCategoryId(tc.getId()),
                   event.getZoneId()))
       .collect(Collectors.toList());
 }
  @RequestMapping("/events/{eventName}/export.csv")
  public void downloadAllTicketsCSV(
      @PathVariable("eventName") String eventName,
      HttpServletRequest request,
      HttpServletResponse response,
      Principal principal)
      throws IOException {
    List<String> fields =
        Arrays.asList(
            Optional.ofNullable(request.getParameterValues("fields")).orElse(new String[] {}));
    Event event = loadEvent(eventName, principal);
    Map<Integer, TicketCategory> categoriesMap =
        eventManager
            .loadTicketCategories(event)
            .stream()
            .collect(Collectors.toMap(TicketCategory::getId, Function.identity()));
    ZoneId eventZoneId = event.getZoneId();

    Predicate<String> contains = FIXED_FIELDS::contains;

    response.setContentType("text/csv;charset=UTF-8");
    response.setHeader("Content-Disposition", "attachment; filename=" + eventName + "-export.csv");

    try (ServletOutputStream out = response.getOutputStream();
        CSVWriter writer = new CSVWriter(new OutputStreamWriter(out))) {

      for (int marker :
          BOM_MARKERS) { // UGLY-MODE_ON: specify that the file is written in UTF-8 with BOM, thanks
                         // to alexr http://stackoverflow.com/a/4192897
        out.write(marker);
      }

      writer.writeNext(fields.toArray(new String[fields.size()]));

      eventManager
          .findAllConfirmedTickets(eventName, principal.getName())
          .stream()
          .map(
              t -> {
                List<String> line = new ArrayList<>();
                if (fields.contains("ID")) {
                  line.add(t.getUuid());
                }
                if (fields.contains("creation")) {
                  line.add(t.getCreation().withZoneSameInstant(eventZoneId).toString());
                }
                if (fields.contains("category")) {
                  line.add(categoriesMap.get(t.getCategoryId()).getName());
                }
                if (fields.contains("event")) {
                  line.add(eventName);
                }
                if (fields.contains("status")) {
                  line.add(t.getStatus().toString());
                }
                if (fields.contains("originalPrice")) {
                  line.add(MonetaryUtil.centsToUnit(t.getSrcPriceCts()).toString());
                }
                if (fields.contains("paidPrice")) {
                  line.add(MonetaryUtil.centsToUnit(t.getFinalPriceCts()).toString());
                }
                if (fields.contains("discount")) {
                  line.add(MonetaryUtil.centsToUnit(t.getDiscountCts()).toString());
                }
                if (fields.contains("vat")) {
                  line.add(MonetaryUtil.centsToUnit(t.getVatCts()).toString());
                }
                if (fields.contains("reservationID")) {
                  line.add(t.getTicketsReservationId());
                }
                if (fields.contains("Full Name")) {
                  line.add(t.getFullName());
                }
                if (fields.contains("First Name")) {
                  line.add(t.getFirstName());
                }
                if (fields.contains("Last Name")) {
                  line.add(t.getLastName());
                }
                if (fields.contains("E-Mail")) {
                  line.add(t.getEmail());
                }
                if (fields.contains("locked")) {
                  line.add(String.valueOf(t.getLockedAssignment()));
                }
                if (fields.contains("Language")) {
                  line.add(String.valueOf(t.getUserLanguage()));
                }

                // obviously not optimized
                Map<String, String> additionalValues =
                    ticketFieldRepository.findAllValuesForTicketId(t.getId());

                fields
                    .stream()
                    .filter(contains.negate())
                    .forEachOrdered(
                        field -> {
                          line.add(additionalValues.getOrDefault(field, "").replaceAll("\"", ""));
                        });

                return line.toArray(new String[line.size()]);
              })
          .forEachOrdered(writer::writeNext);
      writer.flush();
      out.flush();
    }
  }