/**
* Copyright 2009 Google Inc.
*
* 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.waveprotocol.wave.model.document.operation.algorithm;
import org.waveprotocol.wave.model.document.operation.DocOp;
import org.waveprotocol.wave.model.operation.OperationException;
import java.util.ArrayList;
import java.util.List;
import java.util.ListIterator;
/**
* A class that collects document operations together and composes them in an
* efficient manner.
*/
public final class DocOpCollector {
private final List<DocOp> operations = new ArrayList<DocOp>();
public void add(DocOp operation) {
//
// The algorithm below ensures that the compose() calls for a sequence of
// operations are performed in a tree-like manner. In an operation sequence,
// it is generally faster to compose two adjacent ops than it is to compose
// an op with the composition of all ops before it, so this distribution is
// expected to be faster than sequential composition.
//
// The time complexity for composing N ops of total size n is O(n log N),
// rather than O(n^2) for sequential composition.
//
// Illustration of first 8 steps, demonstrating the adjacent composition:
// [a]
// [0, (a;b)]
// [c, (a;b)]
// [0, 0, (a;b);(c;d)]
// [e, 0, (a;b);(c;d)]
// [0, (e;f), (a;b);(c;d)]
// [g, (e;f), (a;b);(c;d)]
// [0, 0, 0, ((a;b);(c;d));((e;f);(g;h)))]
//
// See http://groups.google.com/group/wave-protocol/msg/eb1e7293b26ff61b
//
ListIterator<DocOp> iterator = operations.listIterator();
while (iterator.hasNext()) {
DocOp nextOperation = iterator.next();
if (nextOperation == null) {
iterator.set(operation);
return;
}
iterator.set(null);
operation = compose(nextOperation, operation);
}
operations.add(operation);
}
public DocOp composeAll() {
DocOp result = null;
for (DocOp operation : operations) {
if (operation != null) {
result = (result != null) ? compose(operation, result) : operation;
}
}
operations.clear();
return result;
}
private DocOp compose(DocOp op1, DocOp op2) {
try {
return Composer.compose(op1, op2);
} catch (OperationException e) {
throw new IllegalArgumentException(e);
}
}
public boolean isEmpty() {
return operations.isEmpty();
}
}