flink-table/flink-table-planner/src/main/java/org/apache/flink/table/planner/functions/sql/SqlJsonObjectFunction.java

/*
 * 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.planner.functions.sql;

import org.apache.calcite.rel.type.RelDataType;
import org.apache.calcite.rel.type.RelDataTypeFactory;
import org.apache.calcite.sql.SqlCall;
import org.apache.calcite.sql.SqlCallBinding;
import org.apache.calcite.sql.SqlFunction;
import org.apache.calcite.sql.SqlFunctionCategory;
import org.apache.calcite.sql.SqlJsonConstructorNullClause;
import org.apache.calcite.sql.SqlKind;
import org.apache.calcite.sql.SqlLiteral;
import org.apache.calcite.sql.SqlNode;
import org.apache.calcite.sql.SqlOperandCountRange;
import org.apache.calcite.sql.SqlWriter;
import org.apache.calcite.sql.fun.SqlStdOperatorTable;
import org.apache.calcite.sql.parser.SqlParserPos;
import org.apache.calcite.sql.type.ReturnTypes;
import org.apache.calcite.sql.type.SqlOperandCountRanges;
import org.apache.calcite.sql.type.SqlOperandTypeChecker;
import org.apache.calcite.sql.type.SqlTypeName;
import org.apache.calcite.sql.type.SqlTypeUtil;
import org.apache.calcite.sql.validate.SqlValidator;

import java.util.Locale;

import static org.apache.calcite.util.Static.RESOURCE;

/**
 * This class has been copied from Calcite to backport the fix made during CALCITE-4394.
 *
 * <p>TODO Remove this class with Calcite 1.27 and replace it with {@link
 * SqlStdOperatorTable#JSON_OBJECT}.
 */
public class SqlJsonObjectFunction extends SqlFunction {
    public SqlJsonObjectFunction() {
        super(
                "JSON_OBJECT",
                SqlKind.OTHER_FUNCTION,
                ReturnTypes.VARCHAR_2000,
                (callBinding, returnType, operandTypes) -> {
                    RelDataTypeFactory typeFactory = callBinding.getTypeFactory();
                    for (int i = 0; i < operandTypes.length; i++) {
                        operandTypes[i] =
                                i == 0
                                        ? typeFactory.createSqlType(SqlTypeName.SYMBOL)
                                        : i % 2 == 1
                                                ? typeFactory.createSqlType(SqlTypeName.VARCHAR)
                                                : typeFactory.createTypeWithNullability(
                                                        typeFactory.createSqlType(SqlTypeName.ANY),
                                                        true);
                    }
                },
                null,
                SqlFunctionCategory.SYSTEM);
    }

    @Override
    public SqlOperandCountRange getOperandCountRange() {
        return SqlOperandCountRanges.from(1);
    }

    @Override
    protected void checkOperandCount(
            SqlValidator validator, SqlOperandTypeChecker argType, SqlCall call) {
        assert call.operandCount() % 2 == 1;
    }

    @Override
    public boolean checkOperandTypes(SqlCallBinding callBinding, boolean throwOnFailure) {
        final int count = callBinding.getOperandCount();
        for (int i = 1; i < count; i += 2) {
            RelDataType nameType = callBinding.getOperandType(i);
            if (!SqlTypeUtil.inCharFamily(nameType)) {
                if (throwOnFailure) {
                    throw callBinding.newError(RESOURCE.expectedCharacter());
                }
                return false;
            }
            if (nameType.isNullable()) {
                if (throwOnFailure) {
                    throw callBinding.newError(
                            RESOURCE.argumentMustNotBeNull(callBinding.operand(i).toString()));
                }
                return false;
            }
        }
        return true;
    }

    @Override
    public SqlCall createCall(SqlLiteral functionQualifier, SqlParserPos pos, SqlNode... operands) {
        if (operands[0] == null) {
            operands[0] = SqlLiteral.createSymbol(SqlJsonConstructorNullClause.NULL_ON_NULL, pos);
        }
        return super.createCall(functionQualifier, pos, operands);
    }

    @Override
    public String getSignatureTemplate(int operandsCount) {
        assert operandsCount % 2 == 1;
        StringBuilder sb = new StringBuilder();
        sb.append("{0}(");
        for (int i = 1; i < operandsCount; i++) {
            sb.append(String.format(Locale.ROOT, "{%d} ", i + 1));
        }
        sb.append("{1})");
        return sb.toString();
    }

    @Override
    public void unparse(SqlWriter writer, SqlCall call, int leftPrec, int rightPrec) {
        assert call.operandCount() % 2 == 1;
        final SqlWriter.Frame frame = writer.startFunCall(getName());
        SqlWriter.Frame listFrame = writer.startList("", "");
        for (int i = 1; i < call.operandCount(); i += 2) {
            writer.sep(",");
            writer.keyword("KEY");
            call.operand(i).unparse(writer, leftPrec, rightPrec);
            writer.keyword("VALUE");
            call.operand(i + 1).unparse(writer, leftPrec, rightPrec);
        }
        writer.endList(listFrame);

        SqlJsonConstructorNullClause nullClause = getEnumValue(call.operand(0));
        switch (nullClause) {
            case ABSENT_ON_NULL:
                writer.keyword("ABSENT ON NULL");
                break;
            case NULL_ON_NULL:
                writer.keyword("NULL ON NULL");
                break;
            default:
                throw new IllegalStateException("unreachable code");
        }
        writer.endFunCall(frame);
    }

    private <E extends Enum<E>> E getEnumValue(SqlNode operand) {
        return (E) ((SqlLiteral) operand).getValue();
    }
}