Remove use of Sets.intersection

Author: sylvansson

main/src/main/java/org/mobilitydata/gtfsvalidator/reportsummary/model/ServiceWindow.java

@@ -1,15 +1,14 @@
 package org.mobilitydata.gtfsvalidator.reportsummary.model;
 
-import static java.util.Collections.emptySet;
 import static java.util.stream.Collectors.*;
 
-import com.google.common.collect.Sets;
 import java.time.LocalDate;
 import java.util.*;
 import org.mobilitydata.gtfsvalidator.table.GtfsCalendar;
 import org.mobilitydata.gtfsvalidator.table.GtfsCalendarDate;
 import org.mobilitydata.gtfsvalidator.table.GtfsCalendarDateExceptionType;
 import org.mobilitydata.gtfsvalidator.table.GtfsTrip;
+import org.mobilitydata.gtfsvalidator.util.FuncUtil;
 
 record ServiceWindow(LocalDate startDate, LocalDate endDate) {
   static Optional<ServiceWindow> fromCalendars(
@@ -58,21 +57,19 @@ static Optional<ServiceWindow> fromCalendarsAndCalendarDates(
 
     Set<String> serviceIds = new HashSet<>(trips.stream().map(GtfsTrip::serviceId).toList());
 
-    // We compute the set of days that are removed across all services in
-    // order to shift the start and end dates.
-    Set<LocalDate> removedDays =
+    Map<String, Set<LocalDate>> removedDaysByServiceId =
         calendarDates.stream()
             .filter(
                 d ->
-                    serviceIds.contains(d.serviceId())
-                        && d.exceptionType() == GtfsCalendarDateExceptionType.SERVICE_REMOVED)
+                    d.exceptionType() == GtfsCalendarDateExceptionType.SERVICE_REMOVED
+                        && serviceIds.contains(d.serviceId()))
             .collect(
                 groupingBy(
-                    GtfsCalendarDate::serviceId, mapping(d -> d.date().getLocalDate(), toSet())))
-            .values()
-            .stream()
-            .reduce(Sets::intersection)
-            .orElse(emptySet());
+                    GtfsCalendarDate::serviceId, mapping(d -> d.date().getLocalDate(), toSet())));
+
+    // We compute the set of days that are removed across all services in
+    // order to shift the start and end dates.
+    Set<LocalDate> removedDays = FuncUtil.intersectAll(removedDaysByServiceId.values());
 
     LocalDate startDate = serviceWindowFromCalendars.get().startDate();
     LocalDate endDate = serviceWindowFromCalendars.get().endDate();

main/src/main/java/org/mobilitydata/gtfsvalidator/util/FuncUtil.java

@@ -0,0 +1,25 @@
+package org.mobilitydata.gtfsvalidator.util;
+
+import static java.util.Collections.emptySet;
+
+import java.util.Collection;
+import java.util.HashSet;
+import java.util.Set;
+
+public class FuncUtil {
+  public static <T> Set<T> intersectAll(Collection<Set<T>> sets) {
+    if (sets.isEmpty()) {
+      return emptySet();
+    }
+
+    Set<T> intersection = null;
+    for (Set<T> set : sets) {
+      if (intersection == null) {
+        intersection = new HashSet<>(set);
+      } else {
+        intersection.retainAll(set);
+      }
+    }
+    return intersection;
+  }
+}

main/src/test/java/org/mobilitydata/gtfsvalidator/util/FuncUtilTest.java

@@ -0,0 +1,27 @@
+package org.mobilitydata.gtfsvalidator.util;
+
+import static com.google.common.truth.Truth.assertThat;
+import static java.util.Collections.emptyList;
+import static java.util.Collections.emptySet;
+
+import java.util.List;
+import java.util.Set;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+@RunWith(JUnit4.class)
+public class FuncUtilTest {
+  @Test
+  public void testIntersectAll() {
+    assertThat(
+            FuncUtil.intersectAll(
+                List.of(
+                    Set.of(1, 2, 3, 4, 5, 6),
+                    Set.of(1, 2, 3, 4, 5, 6, 7, 8, 9, 10),
+                    Set.of(2, 4, 6, 8, 10))))
+        .isEqualTo(Set.of(2, 4, 6));
+
+    assertThat(FuncUtil.intersectAll(emptyList())).isEqualTo(emptySet());
+  }
+}