JTableで作成したカレンダー上に複数日予定をJLayerで描画する

class EventBarLayerUI extends LayerUI<JTable> {
  private static final int BAR_HEIGHT = 10;
  private static final int BAR_MARGIN = 2;
  private final List<EventPeriod> events;

  protected EventBarLayerUI(List<EventPeriod> events) {
    super();
    this.events = events;
  }

  @Override public void paint(Graphics g, JComponent c) {
    super.paint(g, c);

    Graphics2D g2 = (Graphics2D) g.create();
    g2.setRenderingHint(
        RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);

    JTable table = (JTable) ((JLayer<?>) c).getView();

    // Assign tracks (lanes) to events
    assignTracksToEvents();

    // Draw a color bar for each event
    for (EventPeriod ev : events) {
      drawEventBars(g2, table, ev);
    }

    g2.dispose();
  }

  /**
   * Assign track numbers to overlapping events.
   */
  private void assignTracksToEvents() {
    int[] tracks = new int[events.size()];
    boolean[] usedTracks = new boolean[events.size()];
    for (int i = 0; i < events.size(); i++) {
      EventPeriod event = events.get(i);
      Arrays.fill(usedTracks, false);
      // Check for overlap with already processed events
      for (int j = 0; j < i; j++) {
        EventPeriod other = events.get(j);
        if (isOverlapping(event, other)) {
          usedTracks[tracks[j]] = true;
        }
      }
      // Assign the smallest available track number
      int track = 0;
      while (track < usedTracks.length && usedTracks[track]) {
        track++;
      }
      tracks[i] = track;
      event.setTrack(track);
    }
  }

  /**
   * Check if two event periods overlap.
   */
  private boolean isOverlapping(EventPeriod e1, EventPeriod e2) {
    boolean b1 = e1.getEndDate().isBefore(e2.getStartDate());
    boolean b2 = e2.getEndDate().isBefore(e1.getStartDate());
    return !(b1 || b2);
  }

  private void drawEventBars(
      Graphics2D g2, JTable table, EventPeriod event) {
    LocalDate calendarStartDate = (LocalDate) table.getModel().getValueAt(0, 0);
    int daysInTable = DayOfWeek.values().length * CalendarViewTableModel.WEEKS;
    LocalDate current = event.getStartDate();
    while (!current.isAfter(event.getEndDate())) {
      long sinceStart = ChronoUnit.DAYS.between(calendarStartDate, current);
      if (sinceStart >= 0 && sinceStart < daysInTable) {
        int consecutiveDays = getConsecutiveDaysAndPaintBar(
            g2, table, event, current);
        current = current.plusDays(consecutiveDays);
      } else {
        current = current.plusDays(1);
      }
    }
  }

  private static void drawEventBar(
      Graphics2D g2, EventPeriod event, Rectangle barRect) {
    Color clr = event.getColor();
    g2.setColor(clr);
    g2.fillRoundRect(barRect.x, barRect.y, barRect.width, barRect.height, 5, 5);
    g2.setColor(clr.darker());
    g2.drawRoundRect(barRect.x, barRect.y, barRect.width, barRect.height, 5, 5);
    boolean b = barRect.width > 60;
    if (b) {
      drawBarTitle(g2, event, barRect);
    }
  }

  private static int getConsecutiveDaysAndPaintBar(
      Graphics2D g2, JTable tbl, EventPeriod ev, LocalDate cur) {
    LocalDate calendarStartDate = (LocalDate) tbl.getModel().getValueAt(0, 0);
    long sinceStart = ChronoUnit.DAYS.between(calendarStartDate, cur);
    int trackOffset = ev.getTrack() * (BAR_HEIGHT + BAR_MARGIN);
    int headerHeight = tbl.getTableHeader().getHeight();
    long daysInWeek = DayOfWeek.values().length;
    int weekRow = (int) (sinceStart / daysInWeek);
    int dayCol = (int) (sinceStart % daysInWeek);

    int consecutiveDays = 1;
    LocalDate nextDay = cur.plusDays(1);
    boolean notEndOfWeek = dayCol != daysInWeek - 1;
    while (!nextDay.isAfter(ev.getEndDate()) && notEndOfWeek) {
      consecutiveDays++;
      nextDay = nextDay.plusDays(1);
      if (dayCol + consecutiveDays >= daysInWeek) {
        break;
      }
    }

    Rectangle firstRect = tbl.getCellRect(weekRow, dayCol, false);
    Rectangle lastRect = tbl.getCellRect(weekRow, dayCol + consecutiveDays - 1, false);

    int barX = firstRect.x + 5;
    int barY = firstRect.y + trackOffset + headerHeight;
    int barWidth = lastRect.x + lastRect.width - firstRect.x - 10;
    drawEventBar(g2, ev, new Rectangle(barX, barY, barWidth, BAR_HEIGHT));
    return consecutiveDays;
  }

  private static void drawBarTitle(Graphics2D g2, EventPeriod event, Rectangle rect) {
    g2.setColor(Color.BLACK);
    g2.setFont(g2.getFont().deriveFont(9f));
    FontMetrics fm = g2.getFontMetrics();
    String eventName = event.getName();
    int textWidth = fm.stringWidth(eventName);
    if (textWidth > rect.width - 6) {
      eventName = eventName.substring(0, Math.min(eventName.length(), 5)) + "...";
    }
    int textX = rect.x + 3;
    int textY = rect.y + rect.height / 2 + fm.getAscent() / 2 - 1;
    g2.drawString(eventName, textX, textY);
  }
}