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A recurrence processor for Java
/*
* Copyright 2022 Marten Gajda
*
*
* 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.
*/
package org.dmfs.rfc5545.instanceiterator;
import org.dmfs.rfc5545.DateTime;
import org.dmfs.rfc5545.InstanceIterator;
import java.util.Locale;
/**
* An iterator for recurrence sets. It takes a number of {@link InstanceIterator}s for instances and exceptions and iterates all resulting instances
* (i.e. only the instances, not the exceptions).
*/
public final class EffectiveInstancesIterator implements InstanceIterator
{
private final static DateTime MAX = new DateTime(1 << 18 - 1, 11, 31, 23, 59, 59);
private final static DateTime MIN = new DateTime(0, 0, 1, 0, 0, 0);
/**
* Throw if we skipped this many instances in a line, because they were exceptions.
*/
private final static int MAX_SKIPPED_INSTANCES = 1000;
private final InstanceIterator mInstances;
private final InstanceIterator mExceptions;
private DateTime mNextInstance = MIN;
private DateTime mNextException = MIN;
/**
* Create a new recurrence iterator for specific lists of instances and exceptions.
*
* @param instances The instances, must not be null
or empty.
* @param exceptions The exceptions, may be null.
*/
public EffectiveInstancesIterator(InstanceIterator instances, InstanceIterator exceptions)
{
mInstances = instances;
mExceptions = exceptions;
pullNext();
}
/**
* Check if there is at least one more instance to iterate.
*
* @return true
if the next call to {@link #next()} will return another instance, false
otherwise.
*/
@Override
public boolean hasNext()
{
return mNextInstance != MAX;
}
/**
* Get the next instance of this set. Do not call this if {@link #hasNext()} returns false
.
*
* @return The time in milliseconds since the epoch of the next instance.
* @throws ArrayIndexOutOfBoundsException if there are no more instances.
*/
@Override
public DateTime next()
{
if (!hasNext())
{
throw new ArrayIndexOutOfBoundsException("no more elements");
}
DateTime result = mNextInstance;
pullNext();
return result;
}
/**
* Fast-forward to the next instance at or after the given date.
*/
@Override
public void fastForward(DateTime until)
{
if (mNextInstance.before(until))
{
mInstances.fastForward(until);
mExceptions.fastForward(until);
pullNext();
}
}
private void pullNext()
{
DateTime next = MAX;
DateTime nextException = mNextException;
int skipableInstances = MAX_SKIPPED_INSTANCES;
while (mInstances.hasNext())
{
next = mInstances.next();
while (nextException.before(next))
{
nextException = mExceptions.hasNext() ? mExceptions.next() : MAX;
}
if (nextException.after(next))
{
break;
}
if (--skipableInstances <= 0)
{
throw new RuntimeException(String.format(Locale.ENGLISH, "Skipped too many (%d) instances", MAX_SKIPPED_INSTANCES));
}
// we've skipped the next instance, this might have been the last one
next = MAX;
}
mNextInstance = next;
mNextException = nextException;
}
}
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