core/src/main/java/org/apache/calcite/sql/fun/SqlJsonArrayFunction.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.sql.SqlCall;
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.InferTypes;
import org.apache.calcite.sql.type.OperandTypes;
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.validate.SqlValidator;

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

import java.util.Locale;

import static java.util.Objects.requireNonNull;

/**
 * The <code>JSON_ARRAY</code> function.
 */
public class SqlJsonArrayFunction extends SqlFunction {
  public SqlJsonArrayFunction() {
    super("JSON_ARRAY", SqlKind.OTHER_FUNCTION, ReturnTypes.VARCHAR_2000,
        InferTypes.ANY_NULLABLE, OperandTypes.VARIADIC, SqlFunctionCategory.SYSTEM);
  }

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

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

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

  @Override public @Nullable String getSignatureTemplate(int operandsCount) {
    assert operandsCount >= 1;
    final 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() >= 1;
    final SqlWriter.Frame frame = writer.startFunCall(getName());
    SqlWriter.Frame listFrame = writer.startList("", "");
    for (int i = 1; i < call.operandCount(); i++) {
      writer.sep(",");
      call.operand(i).unparse(writer, leftPrec, rightPrec);
    }
    writer.endList(listFrame);

    if (call.operandCount() > 1) {
      // If we have only 1 operand the value of 'ON NULL' does not matter.
      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);
  }

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