core/src/main/java/org/apache/calcite/sql/fun/SqlJsonQueryFunction.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.SqlBasicCall;
import org.apache.calcite.sql.SqlCall;
import org.apache.calcite.sql.SqlFunction;
import org.apache.calcite.sql.SqlFunctionCategory;
import org.apache.calcite.sql.SqlJsonQueryEmptyOrErrorBehavior;
import org.apache.calcite.sql.SqlJsonQueryWrapperBehavior;
import org.apache.calcite.sql.SqlKind;
import org.apache.calcite.sql.SqlLiteral;
import org.apache.calcite.sql.SqlNode;
import org.apache.calcite.sql.SqlOperatorBinding;
import org.apache.calcite.sql.SqlWriter;
import org.apache.calcite.sql.parser.SqlParserPos;
import org.apache.calcite.sql.type.OperandTypes;
import org.apache.calcite.sql.type.ReturnTypes;
import org.apache.calcite.sql.type.SqlTypeFamily;
import org.apache.calcite.sql.type.SqlTypeName;
import org.apache.calcite.sql.type.SqlTypeTransforms;
import org.apache.calcite.sql.type.SqlTypeUtil;

import com.google.common.collect.ImmutableList;

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

import java.util.ArrayList;
import java.util.List;
import java.util.Objects;
import java.util.Optional;

import static java.util.Objects.requireNonNull;

/**
 * The <code>JSON_QUERY</code> function.
 */
public class SqlJsonQueryFunction extends SqlFunction {
  public SqlJsonQueryFunction() {
    super("JSON_QUERY", SqlKind.OTHER_FUNCTION,
        ReturnTypes.cascade(
            opBinding ->
                explicitTypeSpec(opBinding)
                    .map(t -> deriveExplicitType(opBinding, t))
                    .orElseGet(() -> getDefaultType(opBinding)),
            SqlTypeTransforms.FORCE_NULLABLE),
        null,
        OperandTypes.family(
            ImmutableList.of(SqlTypeFamily.ANY, SqlTypeFamily.CHARACTER,
            SqlTypeFamily.ANY, SqlTypeFamily.ANY, SqlTypeFamily.ANY, SqlTypeFamily.ANY),
            i -> i >= 5),
        SqlFunctionCategory.SYSTEM);
  }

  /** Returns VARCHAR(2000) as default. */
  private static RelDataType getDefaultType(SqlOperatorBinding opBinding) {
    final RelDataTypeFactory typeFactory = opBinding.getTypeFactory();
    final RelDataType baseType = typeFactory.createSqlType(SqlTypeName.VARCHAR, 2000);
    return typeFactory.createTypeWithNullability(baseType, true);
  }

  private static RelDataType deriveExplicitType(SqlOperatorBinding opBinding, RelDataType type) {
    if (SqlTypeName.ARRAY == type.getSqlTypeName()) {
      RelDataType elementType = Objects.requireNonNull(type.getComponentType());
      RelDataType nullableElementType = deriveExplicitType(opBinding, elementType);
      return SqlTypeUtil.createArrayType(
          opBinding.getTypeFactory(),
          nullableElementType,
          true);
    }
    return opBinding.getTypeFactory().createTypeWithNullability(type, true);
  }

  @Override public @Nullable String getSignatureTemplate(int operandsCount) {
    if (operandsCount == 6) {
      return "{0}({1} {2} RETURNING {6} {3} WRAPPER {4} ON EMPTY {5} ON ERROR)";
    } else {
      return "{0}({1} {2} {3} WRAPPER {4} ON EMPTY {5} ON ERROR)";
    }
  }

  @Override public void unparse(SqlWriter writer, SqlCall call, int leftPrec,
      int rightPrec) {
    final SqlWriter.Frame frame = writer.startFunCall(getName());
    call.operand(0).unparse(writer, 0, 0);
    writer.sep(",", true);
    call.operand(1).unparse(writer, 0, 0);
    if (call.operandCount() == 6) {
      writer.keyword("RETURNING");
      call.operand(5).unparse(writer, 0, 0);
    }
    final SqlJsonQueryWrapperBehavior wrapperBehavior =
        getEnumValue(call.operand(2));
    switch (wrapperBehavior) {
    case WITHOUT_ARRAY:
      writer.keyword("WITHOUT ARRAY");
      break;
    case WITH_CONDITIONAL_ARRAY:
      writer.keyword("WITH CONDITIONAL ARRAY");
      break;
    case WITH_UNCONDITIONAL_ARRAY:
      writer.keyword("WITH UNCONDITIONAL ARRAY");
      break;
    default:
      throw new IllegalStateException("unreachable code");
    }
    writer.keyword("WRAPPER");
    unparseEmptyOrErrorBehavior(writer, getEnumValue(call.operand(3)));
    writer.keyword("ON EMPTY");
    unparseEmptyOrErrorBehavior(writer, getEnumValue(call.operand(4)));
    writer.keyword("ON ERROR");
    writer.endFunCall(frame);
  }

  @Override public SqlCall createCall(@Nullable SqlLiteral functionQualifier,
      SqlParserPos pos, @Nullable SqlNode... operands) {
    final List<SqlNode> args = new ArrayList<>();
    args.add(Objects.requireNonNull(operands[0]));
    args.add(Objects.requireNonNull(operands[1]));

    if (operands[2] == null) {
      args.add(SqlLiteral.createSymbol(SqlJsonQueryWrapperBehavior.WITHOUT_ARRAY, pos));
    } else {
      args.add(operands[2]);
    }
    if (operands[3] == null) {
      args.add(SqlLiteral.createSymbol(SqlJsonQueryEmptyOrErrorBehavior.NULL, pos));
    } else {
      args.add(operands[3]);
    }
    if (operands[4] == null) {
      args.add(SqlLiteral.createSymbol(SqlJsonQueryEmptyOrErrorBehavior.NULL, pos));
    } else {
      args.add(operands[4]);
    }

    if (operands.length >= 6 && operands[5] != null) {
      args.add(operands[5]);
    }

    pos = pos.plusAll(operands);
    return new SqlBasicCall(this, args, pos, functionQualifier);
  }

  private static void unparseEmptyOrErrorBehavior(SqlWriter writer,
      SqlJsonQueryEmptyOrErrorBehavior emptyBehavior) {
    switch (emptyBehavior) {
    case NULL:
      writer.keyword("NULL");
      break;
    case ERROR:
      writer.keyword("ERROR");
      break;
    case EMPTY_ARRAY:
      writer.keyword("EMPTY ARRAY");
      break;
    case EMPTY_OBJECT:
      writer.keyword("EMPTY OBJECT");
      break;
    default:
      throw new IllegalStateException("unreachable code");
    }
  }

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

  public static boolean hasExplicitTypeSpec(List<SqlNode> operands) {
    return operands.size() >= 6;
  }

  public static List<SqlNode> removeTypeSpecOperands(SqlCall call) {
    return call.getOperandList().subList(0, 5);
  }

  /** Returns the optional explicit returning type specification. * */
  private static Optional<RelDataType> explicitTypeSpec(SqlOperatorBinding opBinding) {
    if (opBinding.getOperandCount() >= 6) {
      return Optional.of(opBinding.getOperandType(5));
    }
    return Optional.empty();
  }
}