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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.catalog;

import org.apache.flink.annotation.Internal;
import org.apache.flink.table.api.TableException;
import org.apache.flink.table.delegation.PlannerTypeInferenceUtil;
import org.apache.flink.table.functions.BuiltInFunctionDefinition;
import org.apache.flink.table.functions.FunctionDefinition;
import org.apache.flink.table.functions.FunctionIdentifier;

import java.util.Optional;

/**
 * Catalog of functions that can resolve the name of a function to a {@link FunctionLookup.Result}.
 */
@Internal
public interface FunctionLookup {

	/**
	 * Lookup a function by function identifier. The lookup is case insensitive.
	 */
	Optional lookupFunction(UnresolvedIdentifier identifier);

	/**
	 * Helper method for looking up a built-in function.
	 */
	default Result lookupBuiltInFunction(BuiltInFunctionDefinition definition) {
		return lookupFunction(UnresolvedIdentifier.of(definition.getName()))
			.orElseThrow(() -> new TableException(
				String.format(
					"Required built-in function [%s] could not be found in any catalog.",
					definition.getName())
				)
			);
	}

	/**
	 * Temporary utility until the new type inference is fully functional.
	 */
	PlannerTypeInferenceUtil getPlannerTypeInferenceUtil();

	/**
	 * Result of a function lookup.
	 */
	class Result {

		private final FunctionIdentifier functionIdentifier;

		private final FunctionDefinition functionDefinition;

		public Result(FunctionIdentifier functionIdentifier, FunctionDefinition functionDefinition) {
			this.functionIdentifier = functionIdentifier;
			this.functionDefinition = functionDefinition;
		}

		public FunctionIdentifier getFunctionIdentifier() {
			return functionIdentifier;
		}

		public FunctionDefinition getFunctionDefinition() {
			return functionDefinition;
		}
	}
}