content: /*
   * 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.ReturnTypes;
  import org.apache.calcite.sql.type.SqlSingleOperandTypeChecker;
  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.Optional;
  
  import static org.apache.calcite.sql.type.OperandTypes.family;
  
  import static java.util.Objects.requireNonNull;
  
  /**
   * The <code>JSON_QUERY</code> function.
   */
  public class SqlJsonQueryFunction extends SqlFunction {
    static final SqlSingleOperandTypeChecker TYPE_CHECKER =
        family(
            ImmutableList.of(
                SqlTypeFamily.ANY, SqlTypeFamily.CHARACTER,
                SqlTypeFamily.ANY, SqlTypeFamily.ANY, SqlTypeFamily.ANY))
            .or(
                family(
                    ImmutableList.of(SqlTypeFamily.ANY, SqlTypeFamily.CHARACTER,
                        SqlTypeFamily.ANY, SqlTypeFamily.ANY, SqlTypeFamily.ANY, SqlTypeFamily.ANY)));
  
    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,
          TYPE_CHECKER,
          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 = 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(requireNonNull(operands[0]));
      args.add(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();
    }
  }
  