/*
* 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.nifi.util.file.monitor;
import java.io.IOException;
import java.nio.file.Path;
import java.util.ArrayList;
import java.util.List;
/**
* An {@link UpdateMonitor} that combines multiple <code>UpdateMonitor</code>s such that it will indicate a change in a file only if ALL sub-monitors indicate a change. The sub-monitors will be
* applied in the order given and if any indicates that the state has not changed, the subsequent sub-monitors may not be given a chance to run
*/
public class CompoundUpdateMonitor implements UpdateMonitor {
private final List<UpdateMonitor> monitors;
public CompoundUpdateMonitor(final UpdateMonitor first, final UpdateMonitor... others) {
monitors = new ArrayList<>();
monitors.add(first);
for (final UpdateMonitor monitor : others) {
monitors.add(monitor);
}
}
@Override
public Object getCurrentState(final Path path) throws IOException {
return new DeferredMonitorAction(monitors, path);
}
private static class DeferredMonitorAction {
private static final Object NON_COMPUTED_VALUE = new Object();
private final List<UpdateMonitor> monitors;
private final Path path;
private final Object[] preCalculated;
public DeferredMonitorAction(final List<UpdateMonitor> monitors, final Path path) {
this.monitors = monitors;
this.path = path;
preCalculated = new Object[monitors.size()];
for (int i = 0; i < preCalculated.length; i++) {
preCalculated[i] = NON_COMPUTED_VALUE;
}
}
private Object getCalculatedValue(final int i) throws IOException {
if (preCalculated[i] == NON_COMPUTED_VALUE) {
preCalculated[i] = monitors.get(i).getCurrentState(path);
}
return preCalculated[i];
}
@Override
public boolean equals(final Object obj) {
// must return true unless ALL DeferredMonitorAction's indicate that they are different
if (obj == null) {
return false;
}
if (!(obj instanceof DeferredMonitorAction)) {
return false;
}
final DeferredMonitorAction other = (DeferredMonitorAction) obj;
try {
// Go through each UpdateMonitor's value and check if the value has changed.
for (int i = 0; i < preCalculated.length; i++) {
final Object mine = getCalculatedValue(i);
final Object theirs = other.getCalculatedValue(i);
if (mine == theirs) {
// same
return true;
}
if (mine == null && theirs == null) {
// same
return true;
}
if (mine.equals(theirs)) {
return true;
}
}
} catch (final IOException e) {
return false;
}
// No DeferredMonitorAction was the same as last time. Therefore, it's not equal
return false;
}
}
}