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.sql.SqlCall;
  import org.apache.calcite.sql.SqlIdentifier;
  import org.apache.calcite.sql.SqlInternalOperator;
  import org.apache.calcite.sql.SqlIntervalQualifier;
  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.type.InferTypes;
  import org.apache.calcite.sql.type.OperandTypes;
  import org.apache.calcite.sql.type.SqlReturnTypeInference;
  import org.apache.calcite.sql.type.SqlTypeTransforms;
  
  import static org.apache.calcite.sql.validate.SqlNonNullableAccessors.getOperandLiteralValueOrThrow;
  
  /** Interval expression.
   *
   * <p>Syntax:
   *
   * <blockquote><pre>INTERVAL numericExpression timeUnit
   *
   * timeUnit: YEAR | MONTH | DAY | HOUR | MINUTE | SECOND</pre></blockquote>
   *
   * <p>Compare with interval literal, whose syntax is
   * {@code INTERVAL characterLiteral timeUnit [ TO timeUnit ]}.
   */
  public class SqlIntervalOperator extends SqlInternalOperator {
    private static final SqlReturnTypeInference RETURN_TYPE =
        ((SqlReturnTypeInference) SqlIntervalOperator::returnType)
            .andThen(SqlTypeTransforms.TO_NULLABLE);
  
    SqlIntervalOperator() {
      super("INTERVAL", SqlKind.INTERVAL, 0, true, RETURN_TYPE,
          InferTypes.ANY_NULLABLE, OperandTypes.NUMERIC_INTERVAL);
    }
  
    private static RelDataType returnType(SqlOperatorBinding opBinding) {
      final SqlIntervalQualifier intervalQualifier =
          getOperandLiteralValueOrThrow(opBinding, 1, SqlIntervalQualifier.class);
      return opBinding.getTypeFactory().createSqlIntervalType(intervalQualifier);
    }
  
    @Override public void unparse(SqlWriter writer, SqlCall call, int leftPrec,
        int rightPrec) {
      writer.keyword("INTERVAL");
      final SqlNode expression = call.operand(0);
      final SqlIntervalQualifier intervalQualifier = call.operand(1);
      expression.unparseWithParentheses(writer, leftPrec, rightPrec,
          !(expression instanceof SqlLiteral
              || expression instanceof SqlIdentifier
              || expression.getKind() == SqlKind.MINUS_PREFIX
              || writer.isAlwaysUseParentheses()));
      assert intervalQualifier.timeUnitRange.endUnit == null;
      intervalQualifier.unparse(writer, 0, 0);
    }
  
    @Override public String getSignatureTemplate(int operandsCount) {
      switch (operandsCount) {
      case 2:
        return "{0} {1} {2}"; // e.g. "INTERVAL <INTEGER> <INTERVAL HOUR>"
      default:
        throw new AssertionError();
      }
    }
  }
  