WIP: attempt to support non-gregorian calendars

See #20

src/main/java/com/flowingcode/addons/ycalendar/MonthCalendar.java

@@ -7,9 +7,9 @@
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
- * 
+ *
  *      http://www.apache.org/licenses/LICENSE-2.0
- * 
+ *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
@@ -29,7 +29,16 @@
 import java.time.LocalDate;
 import java.time.Month;
 import java.time.YearMonth;
+import java.time.chrono.ChronoLocalDate;
+import java.time.chrono.Chronology;
+import java.time.chrono.IsoChronology;
+import java.time.temporal.ChronoField;
+import java.time.temporal.ChronoUnit;
+import java.time.temporal.Temporal;
+import java.time.temporal.TemporalAdjusters;
+import java.time.temporal.ValueRange;
 import java.util.Objects;
+import java.util.function.Predicate;
 import java.util.stream.IntStream;
 
 @Tag("fc-month-calendar")
@@ -39,7 +48,20 @@
 @SuppressWarnings("serial")
 public class MonthCalendar extends AbstractCalendarComponent<MonthCalendar> implements HasSize, HasTheme {
 
-  private YearMonth yearMonth;
+  // current yearMonth in ISO Chronology
+  // This is NOT the equivalent date in the ISO calendar, but a date in some month with the same
+  // "shape" (i.e. a month that starts on the same week-day and has the same number of days).
+  // For instance, Dhul Hijjah 1442 is a 29-day month starting on Sunday, 11 July 2021.
+  // The corresponding isoYearMonth is February 2004 (a 29-day month starting on Sunday)
+  private YearMonth isoYearMonth;
+
+  // current yearMonth in the selected Chronology
+  private YearMonth chronoYearMonth;
+
+  // start of the current month in the selected Chronology
+  private ChronoLocalDate chronoLocalDate;
+
+  private Chronology chronology = IsoChronology.INSTANCE;
 
   private ValueProvider<LocalDate, String> classNameGenerator;
 
@@ -53,29 +75,86 @@ public MonthCalendar(YearMonth yearMonth) {
     setYearMonth(yearMonth);
   }
 
+  /**
+   * Creates a new instance of {@code MonthCalendar} for the year, month and calendar system given
+   * by a {@code ChronoLocalDate}.
+   * <p>
+   * This implementation requires that the {@code chronology} has 12-month year and 7-day weeks, and
+   * that all months have between 28 and 31 days.
+   */
+  public MonthCalendar(ChronoLocalDate chronoLocalDate) {
+    chronology = chronoLocalDate.getChronology();
+    validateChronology(chronology);
+    setYearMonth(YearMonth.of(chronoLocalDate.get(ChronoField.YEAR),
+        chronoLocalDate.get(ChronoField.MONTH_OF_YEAR)));
+  }
+
   public void setReadOnly(boolean readOnly) {
     getElement().setAttribute("readonly", readOnly);
   }
 
   /** Returns the year-and-month that is displayed in this calendar. */
   public YearMonth getYearMonth() {
-    return yearMonth;
+    return chronoYearMonth;
   }
 
   /** Returns the month-of-year that is displayed in this calendar. */
   public Month getMonth() {
-    return yearMonth.getMonth();
+    return chronoYearMonth.getMonth();
   }
 
   /** Sets the year-and-month that is displayed in this calendar. */
   public void setYearMonth(YearMonth yearMonth) {
-    this.yearMonth = Objects.requireNonNull(yearMonth);
-    this.yearMonth = Objects.requireNonNull(yearMonth);
+    chronoYearMonth = Objects.requireNonNull(yearMonth);
+
     String script = "this.month=new Date($0,$1-1,1);";
-    getElement().executeJs(script, yearMonth.getYear(), yearMonth.getMonthValue());
+    int year = chronoYearMonth.get(ChronoField.YEAR);
+    int month = chronoYearMonth.get(ChronoField.MONTH_OF_YEAR);
+    chronoLocalDate = chronology.date(year, month, 1);
+
+    if (chronology instanceof IsoChronology) {
+      // for ISO chronology use the default implementation of vaadin-month-calendar
+      script = "this._chronology={}; " + script;
+      getElement().executeJs(script, year, month);
+      isoYearMonth = chronoYearMonth;
+    } else {
+      isoYearMonth = findIsoYearMonth(chronoLocalDate);
+
+      int isoYear = isoYearMonth.get(ChronoField.YEAR);
+      int isoMonth = isoYearMonth.get(ChronoField.MONTH_OF_YEAR);
+
+      script = "this._chronology={year:$2, month:$3}; " + script;
+      getElement().executeJs(script, isoYear, isoMonth, year, month);
+    }
+
     refreshAll();
   }
-
+
+  private static int getDaysInMonth(Temporal t) {
+    return t.with(TemporalAdjusters.lastDayOfMonth()).get(ChronoField.DAY_OF_MONTH);
+  }
+
+  private static YearMonth findIsoYearMonth(ChronoLocalDate chronoDate) {
+    // find a month that starts in the same day of week as the chronoDate
+    // and has the same number of days in month
+
+    Integer dayOfWeek = chronoDate.get(ChronoField.DAY_OF_WEEK);
+    Integer daysInMonth = (int) chronoDate.range(ChronoField.DAY_OF_MONTH).getMaximum();
+
+    LocalDate date = LocalDate.of(2000, 2, 1);
+    if (daysInMonth == 29) {
+      while (date.get(ChronoField.DAY_OF_WEEK) != dayOfWeek) {
+        date = date.plusYears(4);
+      }
+    } else {
+      while (date.get(ChronoField.DAY_OF_WEEK) != dayOfWeek
+          || getDaysInMonth(date) != daysInMonth) {
+        date = date.plusMonths(1);
+      }
+    }
+    return YearMonth.from(date);
+  }
+
   /**
    * Sets the function that is used for generating CSS class names for rows in this calendar.
    * Returning {@code null} from the generator results in no custom class name being set. Multiple
@@ -91,10 +170,11 @@ public void setClassNameGenerator(ValueProvider<LocalDate, String> classNameGene
    */
   @Override
   public void refreshAll() {
-    IntStream.rangeClosed(1, yearMonth.lengthOfMonth()).forEach(dayOfMonth -> {
+    IntStream.rangeClosed(1, chronoYearMonth.lengthOfMonth()).forEach(dayOfMonth -> {
       String className;
       if (classNameGenerator != null) {
-        className = classNameGenerator.apply(yearMonth.atDay(dayOfMonth));
+        className = classNameGenerator
+            .apply(LocalDate.from(chronoLocalDate.plus(dayOfMonth - 1, ChronoUnit.DAYS)));
       } else {
         className = null;
       }
@@ -108,10 +188,12 @@ public void refreshAll() {
    * @throws IllegalArgumentException if the displayed year-and-month does not contain {@code date}.
    */
   public void refreshItem(LocalDate date) {
-    if (date.getYear() == yearMonth.getYear() && date.getMonth() == yearMonth.getMonth()) {
+    if (date.getYear() == chronoYearMonth.getYear()
+        && date.getMonth() == chronoYearMonth.getMonth()) {
       String className;
       if (classNameGenerator != null) {
-        className = classNameGenerator.apply(date);
+        LocalDate isoDate = isoYearMonth.atDay(date.getDayOfMonth());
+        className = classNameGenerator.apply(isoDate);
       } else {
         className = null;
       }
@@ -125,4 +207,30 @@ private void setStyleForDay(int dayOfMonth, String className) {
     getElement().executeJs("setTimeout(()=>{this._setStyleForDay($0,$1);})", dayOfMonth, className);
   }
 
+
+  private void validate(Chronology chronology, ChronoField field, Predicate<ValueRange> predicate) {
+    ValueRange range = chronology.range(field);
+    if (!predicate.test(range)) {
+      throw new IllegalArgumentException(
+          String.format("Unsupported Chronology %s (%s out of range)", chronology, field));
+    }
+  }
+
+  private void validateChronology(Chronology chronology) {
+    if (chronology != null) {
+      // Check that all weeks have 7 days
+      validate(chronology, ChronoField.DAY_OF_WEEK, range -> range.getMaximum() == 7);
+      validate(chronology, ChronoField.DAY_OF_WEEK, range -> range.getSmallestMaximum() == 7);
+      validate(chronology, ChronoField.DAY_OF_WEEK, range -> range.getLargestMinimum() == 1);
+      // Check that all years have 12 months
+      validate(chronology, ChronoField.MONTH_OF_YEAR, range -> range.getMaximum() == 12);
+      validate(chronology, ChronoField.MONTH_OF_YEAR, range -> range.getSmallestMaximum() == 12);
+      validate(chronology, ChronoField.MONTH_OF_YEAR, range -> range.getLargestMinimum() == 1);
+      // Check that all months have between 28 and 31 days
+      validate(chronology, ChronoField.DAY_OF_MONTH, range -> range.getMaximum() <= 31);
+      validate(chronology, ChronoField.DAY_OF_MONTH, range -> range.getSmallestMaximum() >= 28);
+      validate(chronology, ChronoField.DAY_OF_MONTH, range -> range.getLargestMinimum() == 1);
+    }
+  }
+
 }

src/main/resources/META-INF/frontend/fc-month-calendar/month-calendar-mixin.js

@@ -56,6 +56,10 @@ export class MonthCalendarMixin extends ShadowFocusMixin(ThemableMixin(PolymerEl
         value: false
       },
 
+      _chronology: {
+        type: Object
+      },
+
       i18n: {
         type: Object
       },
@@ -123,6 +127,9 @@ export class MonthCalendarMixin extends ShadowFocusMixin(ThemableMixin(PolymerEl
             </vaadin-month-calendar>
 	`;}
 
+	ready() {
+		super.ready();
+	}
 
 }
 

src/test/java/com/flowingcode/addons/ycalendar/MonthDemoHijrah.java

@@ -0,0 +1,69 @@
+/*-
+ * #%L
+ * Year Month Calendar Add-on
+ * %%
+ * Copyright (C) 2021 - 2022 Flowing Code
+ * %%
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ * #L%
+ */
+package com.flowingcode.addons.ycalendar;
+
+import com.flowingcode.vaadin.addons.demo.DemoSource;
+import com.vaadin.flow.component.datepicker.DatePicker;
+import com.vaadin.flow.component.dependency.CssImport;
+import com.vaadin.flow.component.html.Div;
+import com.vaadin.flow.component.html.Span;
+import com.vaadin.flow.component.orderedlayout.HorizontalLayout;
+import com.vaadin.flow.router.PageTitle;
+import com.vaadin.flow.router.Route;
+import java.time.DayOfWeek;
+import java.time.chrono.HijrahChronology;
+import java.util.Arrays;
+
+@DemoSource
+@PageTitle("Month")
+@CssImport(value = "./styles/test_year-month-calendar.css", themeFor = "vaadin-month-calendar")
+@Route(value = "year-month-calendar/month-hijrah", layout = YearMonthCalendarDemoView.class)
+public class MonthDemoHijrah extends Div {
+
+  public MonthDemoHijrah() {
+
+    MonthCalendar calendar = new MonthCalendar(HijrahChronology.INSTANCE.dateNow());
+
+    calendar.setClassNameGenerator(date -> {
+      if (TestUtils.isHijrahHoliday(date)) {
+        return "holiday";
+      }
+      if (date.getDayOfWeek() == DayOfWeek.SATURDAY || date.getDayOfWeek() == DayOfWeek.SUNDAY) {
+        return "weekend";
+      }
+      return null;
+    });
+
+    DatePicker.DatePickerI18n i18n = new DatePicker.DatePickerI18n();
+    i18n.setMonthNames(Arrays.asList("al-Muḥarram", "Ṣafar", "Rabīʿ al-ʾAwwal", "Rabīʿ ath-Thānī",
+        "Rabīʿ al-ʾĀkhir", "Jumādā al-ʾŪlā", "Jumādā ath-Thāniyah", "Jumādā al-ʾĀkhirah", "Rajab",
+        "Shaʿbān", "Ramaḍān", "Shawwāl", "Ḏū al-Qaʿdah", "Ḏū al-Ḥijjah"));
+    // calendar.setI18n(i18n);
+
+    Span selectedDate = new Span();
+    calendar.addDateSelectedListener(ev -> {
+      selectedDate.setText("Selected date: " + ev.getDate());
+    });
+
+    Span instructions = new Span("Use arrow keys to move.");
+    add(new HorizontalLayout(instructions, selectedDate), calendar);
+  }
+
+}

src/test/java/com/flowingcode/addons/ycalendar/TestUtils.java

@@ -7,9 +7,9 @@
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
- * 
+ *
  *      http://www.apache.org/licenses/LICENSE-2.0
- * 
+ *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
@@ -20,6 +20,8 @@
 package com.flowingcode.addons.ycalendar;
 
 import java.time.LocalDate;
+import java.time.chrono.HijrahDate;
+import java.time.temporal.ChronoField;
 import java.util.Arrays;
 import java.util.HashSet;
 import java.util.List;
@@ -85,4 +87,21 @@ public static boolean isPublicHoliday(LocalDate date) {
     }
   }
 
+  public static boolean isHijrahHoliday(LocalDate date) {
+    HijrahDate hdate = HijrahDate.from(date);
+    switch (hdate.get(ChronoField.MONTH_OF_YEAR)) {
+      case 1:
+        // 1st Muharram
+        return hdate.get(ChronoField.DAY_OF_MONTH) == 1;
+      case 10:
+        // 1st Shawwal
+        return hdate.get(ChronoField.DAY_OF_MONTH) == 1;
+      case 12:
+        // 10 Dhul Hijjah
+        return hdate.get(ChronoField.DAY_OF_MONTH) == 10;
+      default:
+        return false;
+    }
+  }
+
 }