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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;

import org.apache.flink.annotation.Internal;
import org.apache.flink.table.api.ApiExpression;
import org.apache.flink.table.api.ValidationException;
import org.apache.flink.table.catalog.ContextResolvedFunction;
import org.apache.flink.table.catalog.FunctionLookup;
import org.apache.flink.table.expressions.Expression;
import org.apache.flink.table.expressions.LookupCallExpression;
import org.apache.flink.table.expressions.UnresolvedCallExpression;
import org.apache.flink.table.expressions.utils.ApiExpressionDefaultVisitor;

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

import static org.apache.flink.table.expressions.ApiExpressionUtils.unresolvedCall;

/** Resolves calls with function names to calls with actual function definitions. */
@Internal
public class LookupCallResolver extends ApiExpressionDefaultVisitor {

    private final FunctionLookup functionLookup;

    public LookupCallResolver(FunctionLookup functionLookup) {
        this.functionLookup = functionLookup;
    }

    public Expression visit(LookupCallExpression lookupCall) {
        final ContextResolvedFunction resolvedFunction =
                functionLookup
                        .lookupFunction(lookupCall.getUnresolvedName())
                        .orElseThrow(
                                () ->
                                        new ValidationException(
                                                "Undefined function: "
                                                        + lookupCall.getUnresolvedName()));

        return unresolvedCall(resolvedFunction, resolveChildren(lookupCall.getChildren()));
    }

    public Expression visit(UnresolvedCallExpression unresolvedCall) {
        return unresolvedCall.replaceArgs(resolveChildren(unresolvedCall.getChildren()));
    }

    private List resolveChildren(List lookupChildren) {
        return lookupChildren.stream()
                .map(child -> child.accept(this))
                .collect(Collectors.toList());
    }

    @Override
    public Expression visitNonApiExpression(Expression other) {
        // LookupCallResolver might be called outside of ExpressionResolver, thus we need to
        // additionally handle the ApiExpressions here
        if (other instanceof ApiExpression) {
            return ((ApiExpression) other).toExpr().accept(this);
        } else {
            return defaultMethod(other);
        }
    }

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