core/src/main/java/org/apache/calcite/sql/fun/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.calcite.sql.fun;

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.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 org.checkerframework.checker.nullness.qual.Nullable;

import java.util.Locale;

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

import static java.util.Objects.requireNonNull;

/**
 * The <code>JSON_OBJECT</code> function.
 */
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,
      @Nullable 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(@Nullable SqlLiteral functionQualifier,
      SqlParserPos pos, @Nullable SqlNode... operands) {
    if (operands[0] == null) {
      operands[0] =
          SqlLiteral.createSymbol(SqlJsonConstructorNullClause.NULL_ON_NULL, pos);
    }
    return super.createCall(functionQualifier, pos, operands);
  }

  @Override public @Nullable 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));
    writer.keyword(nullClause.sql);
    writer.endFunCall(frame);
  }

  @SuppressWarnings("unchecked")
  private static <E extends Enum<E>> E getEnumValue(SqlNode operand) {
    return (E) requireNonNull(((SqlLiteral) operand).getValue(), "operand.value");
  }
}