Added comparator for temporalamount interface

src/main/java/net/fortuna/ical4j/model/TemporalAmountComparator.java

@@ -0,0 +1,54 @@
+package net.fortuna.ical4j.model;
+
+import java.time.Duration;
+import java.time.Period;
+import java.time.temporal.TemporalAmount;
+import java.util.Comparator;
+
+public class TemporalAmountComparator implements Comparator<TemporalAmount> {
+    @Override
+    public int compare(TemporalAmount o1, TemporalAmount o2) {
+        int result = 0;
+        if (!o1.getClass().equals(o2.getClass())) {
+//            throw new UnsupportedOperationException("Unable to compare different Temporal types");
+            boolean o1datebased = o1.getUnits().stream().anyMatch(u -> u.isDateBased());
+            boolean o2datebased = o2.getUnits().stream().anyMatch(u -> u.isDateBased());
+            if (o1datebased != o2datebased) {
+                if (o1datebased) {
+                    result = Integer.MAX_VALUE;
+                } else {
+                    result = Integer.MIN_VALUE;
+                }
+            }
+        } else if (o1 instanceof Period && o2 instanceof Period) {
+            Period p1 = (Period) o1, p2 = (Period) o2;
+            if (p1.isNegative() != p2.isNegative()) {
+                if (p1.isNegative()) {
+                    result = Integer.MIN_VALUE;
+                }
+                else {
+                    result = Integer.MAX_VALUE;
+                }
+            }
+            else if (p1.getYears() != p2.getYears()) {
+                result = p1.getYears() - p2.getYears();
+            }
+            else if (p1.getMonths() != p2.getMonths()) {
+                result = p1.getMonths() - p2.getMonths();
+            }
+            else {
+                result = p1.getDays() - p2.getDays();
+            }
+            // invert sense of all tests if both durations are negative
+            if (p1.isNegative()) {
+                return -result;
+            }
+            else {
+                return result;
+            }
+        } else {
+            result =  Duration.from(o1).compareTo(Duration.from(o2));
+        }
+        return result;
+    }
+}

src/test/groovy/net/fortuna/ical4j/model/TemporalAmountComparatorTest.groovy

@@ -0,0 +1,24 @@
+package net.fortuna.ical4j.model
+
+import spock.lang.Specification
+
+import java.time.Duration
+
+class TemporalAmountComparatorTest extends Specification {
+
+    TemporalAmountComparator comparator = []
+
+    def 'assert comparison is correct'() {
+        expect:
+        comparator.compare(o1, o2) == expectedResult
+
+        where:
+        o1                      | o2                   | expectedResult
+        Duration.ofDays(1)  | Duration.ofDays(2)       | -1
+        Duration.ofHours(-2)  | Duration.ofHours(2)       | -1
+        java.time.Period.ofDays(3)  | java.time.Period.ofDays(2) | 1
+        java.time.Period.ofMonths(12)  | java.time.Period.ofYears(1) | -1
+        java.time.Period.ofMonths(12)  | java.time.Period.ofMonths(12) | 0
+        java.time.Period.ofDays(1)  | java.time.Duration.ofDays(1) | Integer.MAX_VALUE
+    }
+}