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// Copyright (C) 2022 The Android Open Source Project
//
// 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 com.google.gerrit.index.query;
import static com.google.common.base.Preconditions.checkArgument;
import com.google.common.collect.FluentIterable;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Iterables;
import com.google.common.collect.Ordering;
import com.google.gerrit.exceptions.StorageException;
import com.google.gerrit.index.IndexConfig;
import com.google.gerrit.index.PaginationType;
import com.google.gerrit.index.QueryOptions;
import java.util.ArrayList;
import java.util.List;
public class PaginatingSource<T> implements DataSource<T> {
protected final DataSource<T> source;
private final int start;
private final int cardinality;
private final IndexConfig indexConfig;
public PaginatingSource(DataSource<T> source, int start, IndexConfig indexConfig) {
checkArgument(start >= 0, "negative start: %s", start);
this.source = source;
this.start = start;
this.cardinality = source.getCardinality();
this.indexConfig = indexConfig;
}
@Override
public ResultSet<T> read() {
if (source == null) {
throw new StorageException("No DataSource: " + this);
}
// ResultSets are lazy. Calling #read here first and then dealing with ResultSets only when
// requested allows the index to run asynchronous queries.
ResultSet<T> resultSet = source.read();
return new LazyResultSet<>(
() -> {
List<T> r = new ArrayList<>();
T last = null;
int pageResultSize = 0;
for (T data : buffer(resultSet)) {
if (!isMatchable() || match(data)) {
r.add(data);
}
last = data;
pageResultSize++;
}
if (last != null
&& source instanceof Paginated
// TODO: this fix is only for the stable branches and the real refactoring would be to
// restore the logic
// for the filtering in AndSource (L58 - 64) as per
// https://gerrit-review.googlesource.com/c/gerrit/+/345634/9
&& !indexConfig.paginationType().equals(PaginationType.NONE)) {
// Restart source and continue if we have not filled the
// full limit the caller wants.
//
@SuppressWarnings("unchecked")
Paginated<T> p = (Paginated<T>) source;
QueryOptions opts = p.getOptions();
final int limit = opts.limit();
int pageSize = opts.pageSize();
int pageSizeMultiplier = opts.pageSizeMultiplier();
Object searchAfter = resultSet.searchAfter();
int nextStart = pageResultSize;
while (pageResultSize == pageSize && r.size() <= limit) { // get 1 more than the limit
pageSize = getNextPageSize(pageSize, pageSizeMultiplier);
ResultSet<T> next =
indexConfig.paginationType().equals(PaginationType.SEARCH_AFTER)
? p.restart(searchAfter, pageSize)
: p.restart(nextStart, pageSize);
pageResultSize = 0;
for (T data : buffer(next)) {
if (match(data)) {
r.add(data);
}
pageResultSize++;
if (r.size() > limit) {
break;
}
}
nextStart += pageResultSize;
searchAfter = next.searchAfter();
}
}
if (start >= r.size()) {
return ImmutableList.of();
} else if (start > 0) {
return ImmutableList.copyOf(r.subList(start, r.size()));
}
return ImmutableList.copyOf(r);
});
}
@Override
public ResultSet<FieldBundle> readRaw() {
// TOOD(hiesel): Implement
throw new UnsupportedOperationException("not implemented");
}
private Iterable<T> buffer(ResultSet<T> scanner) {
return FluentIterable.from(Iterables.partition(scanner, 50))
.transformAndConcat(this::transformBuffer);
}
protected boolean match(T object) {
return true;
}
protected boolean isMatchable() {
return true;
}
protected List<T> transformBuffer(List<T> buffer) {
return buffer;
}
@Override
public int getCardinality() {
return cardinality;
}
private int getNextPageSize(int pageSize, int pageSizeMultiplier) {
List<Integer> possiblePageSizes = new ArrayList<>(3);
try {
possiblePageSizes.add(Math.multiplyExact(pageSize, pageSizeMultiplier));
} catch (ArithmeticException e) {
possiblePageSizes.add(Integer.MAX_VALUE);
}
if (indexConfig.maxPageSize() > 0) {
possiblePageSizes.add(indexConfig.maxPageSize());
}
if (indexConfig.maxLimit() > 0) {
possiblePageSizes.add(indexConfig.maxLimit());
}
return Ordering.natural().min(possiblePageSizes);
}
}
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