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/*
* All content copyright Terracotta, Inc., unless otherwise indicated.
*
* 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.terracotta.context.query;
import org.terracotta.context.TreeNode;
/**
* A {@code QueryBuilder} allows for modular assembly of context graph queries.
*
* Query assembly is performed by chaining a sequence of graph traversal and
* filtering operations together in order to select a particular set of the
* input node set's descendants.
*/
public class QueryBuilder {
private Query current;
private QueryBuilder() {
current = NullQuery.INSTANCE;
}
/**
* Creates a new query builder instance.
*
* A newly constructed query builder represents the identity query. It simply
* returns the input node set as the output node set.
*
* @return a new query builder
*/
public static QueryBuilder queryBuilder() {
return new QueryBuilder();
}
/**
* Filters the current node set using the supplied {@code Matcher}.
*
* Nodes in the current node set that are not selected by the supplied matcher
* are removed.
*
* @param filter matcher to apply
* @return this query builder
*/
public QueryBuilder filter(Matcher filter) {
return chain(new Filter(filter));
}
/**
* Selects the union of the current node sets child nodes.
*
* @return this query builder
*/
public QueryBuilder children() {
return chain(Children.INSTANCE);
}
/**
* Selects the merged descendant set of the current node set.
*
* More precisely this recursively merges the children of each member of the
* node-set in to the output node set until the set ceases to grow.
*
* @return this query builder
*/
public QueryBuilder descendants() {
return chain(Descendants.INSTANCE);
}
/**
* Applies the given query on the currently selected node set.
*
* @param query query to apply
* @return this query builder
*/
public QueryBuilder chain(Query query) {
current = new ChainedQuery(current, query);
return this;
}
/**
* Asserts that the current node set is a singleton.
*
* If the current node set is not of size 1 then the query will terminate with
* an {@code IllegalStateException}.
*
* @return this query builder
*/
public QueryBuilder ensureUnique() {
return chain(EnsureUnique.INSTANCE);
}
/**
* Selects an empty node set.
*
* @return this query builder
*/
public QueryBuilder empty() {
current = EmptyQuery.INSTANCE;
return this;
}
/**
* Returns a query that represents the currently assembled transformation.
*
* @return a newly constructed query
*/
public Query build() {
return current;
}
}