/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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.
*/
package org.apache.beam.sdk.transforms.windowing;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import org.apache.beam.sdk.annotations.Internal;
/**
* <b>For internal use only; no backwards compatibility guarantees.</b>
*
* <p>A utility function for merging overlapping {@link IntervalWindow IntervalWindows}.
*/
@Internal
public class MergeOverlappingIntervalWindows {
/**
* Merge overlapping {@link IntervalWindow}s.
*/
public static void mergeWindows(WindowFn<?, IntervalWindow>.MergeContext c) throws Exception {
// Merge any overlapping windows into a single window.
// Sort the list of existing windows so we only have to
// traverse the list once rather than considering all
// O(n^2) window pairs.
List<IntervalWindow> sortedWindows = new ArrayList<>();
for (IntervalWindow window : c.windows()) {
sortedWindows.add(window);
}
Collections.sort(sortedWindows);
List<MergeCandidate> merges = new ArrayList<>();
MergeCandidate current = new MergeCandidate();
for (IntervalWindow window : sortedWindows) {
if (current.intersects(window)) {
current.add(window);
} else {
merges.add(current);
current = new MergeCandidate(window);
}
}
merges.add(current);
for (MergeCandidate merge : merges) {
merge.apply(c);
}
}
private static class MergeCandidate {
private IntervalWindow union;
private final List<IntervalWindow> parts;
public MergeCandidate() {
parts = new ArrayList<>();
}
public MergeCandidate(IntervalWindow window) {
union = window;
parts = new ArrayList<>(Arrays.asList(window));
}
public boolean intersects(IntervalWindow window) {
return union == null || union.intersects(window);
}
public void add(IntervalWindow window) {
union = union == null ? window : union.span(window);
parts.add(window);
}
public void apply(WindowFn<?, IntervalWindow>.MergeContext c) throws Exception {
if (parts.size() > 1) {
c.merge(parts, union);
}
}
@Override
public String toString() {
return "MergeCandidate[union=" + union + ", parts=" + parts + "]";
}
}
}