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This module contains the Table/SQL API for writing table programs within the table ecosystem using the Java programming language.

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/*
 * 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.flink.table.expressions.resolver.rules;

import org.apache.flink.annotation.Internal;
import org.apache.flink.table.catalog.FunctionLookup;
import org.apache.flink.table.catalog.ObjectIdentifier;
import org.apache.flink.table.expressions.Expression;
import org.apache.flink.table.expressions.UnresolvedCallExpression;
import org.apache.flink.table.functions.BuiltInFunctionDefinition;

import java.util.List;
import java.util.stream.Collectors;

/**
 * Looks up built-in functions in a catalog for retrieving a fully qualified {@link ObjectIdentifier}.
 */
@Internal
class QualifyBuiltInFunctionsRule implements ResolverRule {

	@Override
	public List apply(List expression, ResolutionContext context) {
		return expression.stream()
			.map(expr -> expr.accept(new QualifyBuiltInFunctionVisitor(context)))
			.collect(Collectors.toList());
	}

	private class QualifyBuiltInFunctionVisitor extends RuleExpressionVisitor {

		QualifyBuiltInFunctionVisitor(ResolutionContext resolutionContext) {
			super(resolutionContext);
		}

		@Override
		public Expression visit(UnresolvedCallExpression unresolvedCall) {
			if (!unresolvedCall.getFunctionIdentifier().isPresent() &&
					unresolvedCall.getFunctionDefinition() instanceof BuiltInFunctionDefinition) {
				final FunctionLookup.Result functionLookup = resolutionContext
					.functionLookup()
					.lookupBuiltInFunction(((BuiltInFunctionDefinition) unresolvedCall.getFunctionDefinition()));

				return new UnresolvedCallExpression(
					functionLookup.getFunctionIdentifier(),
					functionLookup.getFunctionDefinition(),
					unresolvedCall.getChildren().stream()
						.map(c -> c.accept(this))
						.collect(Collectors.toList()));
			}

			return unresolvedCall;
		}

		@Override
		protected Expression defaultMethod(Expression expression) {
			return expression;
		}
	}
}