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.SqlAggFunction;
  import org.apache.calcite.sql.SqlFunctionCategory;
  import org.apache.calcite.sql.SqlKind;
  import org.apache.calcite.sql.SqlOperatorBinding;
  import org.apache.calcite.sql.type.OperandTypes;
  import org.apache.calcite.sql.type.SqlReturnTypeInference;
  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.SqlTypeTransform;
  import org.apache.calcite.sql.type.SqlTypeTransforms;
  import org.apache.calcite.util.Optionality;
  
  import java.util.ArrayList;
  import java.util.List;
  
  import static com.google.common.base.Preconditions.checkArgument;
  
  /**
   * <code>LEAD</code> and <code>LAG</code> aggregate functions
   * return the value of given expression evaluated at given offset.
   */
  public class SqlLeadLagAggFunction extends SqlAggFunction {
    private static final SqlSingleOperandTypeChecker OPERAND_TYPES =
        OperandTypes.ANY
            .or(OperandTypes.ANY_NUMERIC)
            .or(OperandTypes.ANY_NUMERIC_ANY
                // "same" only checks if two types are comparable
                .and(OperandTypes.same(3, 0, 2)));
  
    // A version of least restrictive which only looks at operands 0 and 2,
    // if the latter exists.
    private static final SqlReturnTypeInference ARG03 = opBinding -> {
      List<RelDataType> toCheck = new ArrayList<>();
      toCheck.add(opBinding.getOperandType(0));
      if (opBinding.getOperandCount() >= 3) {
        RelDataType op2 = opBinding.getOperandType(2);
        toCheck.add(op2);
      }
      // If any operand is in the CHAR type family, return VARCHAR.
      for (RelDataType type : toCheck) {
        if (type.getFamily() == SqlTypeFamily.CHARACTER) {
          return opBinding.getTypeFactory().createSqlType(SqlTypeName.VARCHAR);
        }
      }
      return opBinding.getTypeFactory().leastRestrictive(toCheck);
    };
  
    private static final SqlReturnTypeInference RETURN_TYPE =
        ARG03.andThen(SqlLeadLagAggFunction::transformType);
  
    public SqlLeadLagAggFunction(SqlKind kind) {
      super(kind.name(),
          null,
          kind,
          RETURN_TYPE,
          null,
          OPERAND_TYPES,
          SqlFunctionCategory.NUMERIC,
          false,
          true,
          Optionality.FORBIDDEN);
      checkArgument(kind == SqlKind.LEAD || kind == SqlKind.LAG);
    }
  
    @Deprecated // to be removed before 2.0
    public SqlLeadLagAggFunction(boolean isLead) {
      this(isLead ? SqlKind.LEAD : SqlKind.LAG);
    }
  
    // Result is NOT NULL if NOT NULL default value is provided
    private static RelDataType transformType(SqlOperatorBinding binding,
        RelDataType type) {
      SqlTypeTransform transform =
          binding.getOperandCount() < 3 || binding.getOperandType(2).isNullable()
              ? SqlTypeTransforms.FORCE_NULLABLE
              : SqlTypeTransforms.TO_NOT_NULLABLE;
      return transform.transformType(binding, type);
    }
  
    @Override public boolean allowsFraming() {
      return false;
    }
  
    @Override public boolean allowsNullTreatment() {
      return true;
    }
  
  }
  