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.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");
    }
  }
  