exec/java-exec/src/main/java/org/apache/drill/exec/compile/sig/ConstantExpressionIdentifier.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.drill.exec.compile.sig;

import java.util.Collections;
import java.util.IdentityHashMap;
import java.util.List;
import java.util.Set;

import org.apache.drill.common.expression.AnyValueExpression;
import org.apache.drill.common.expression.BooleanOperator;
import org.apache.drill.common.expression.CastExpression;
import org.apache.drill.common.expression.ConvertExpression;
import org.apache.drill.common.expression.FunctionCall;
import org.apache.drill.common.expression.FunctionHolderExpression;
import org.apache.drill.common.expression.IfExpression;
import org.apache.drill.common.expression.LogicalExpression;
import org.apache.drill.common.expression.NullExpression;
import org.apache.drill.common.expression.SchemaPath;
import org.apache.drill.common.expression.TypedFieldExpr;
import org.apache.drill.common.expression.TypedNullConstant;
import org.apache.drill.common.expression.ValueExpressions;
import org.apache.drill.common.expression.ValueExpressions.BooleanExpression;
import org.apache.drill.common.expression.ValueExpressions.DateExpression;
import org.apache.drill.common.expression.ValueExpressions.Decimal18Expression;
import org.apache.drill.common.expression.ValueExpressions.Decimal28Expression;
import org.apache.drill.common.expression.ValueExpressions.Decimal38Expression;
import org.apache.drill.common.expression.ValueExpressions.Decimal9Expression;
import org.apache.drill.common.expression.ValueExpressions.DoubleExpression;
import org.apache.drill.common.expression.ValueExpressions.IntervalDayExpression;
import org.apache.drill.common.expression.ValueExpressions.IntervalYearExpression;
import org.apache.drill.common.expression.ValueExpressions.LongExpression;
import org.apache.drill.common.expression.ValueExpressions.QuotedString;
import org.apache.drill.common.expression.ValueExpressions.TimeExpression;
import org.apache.drill.common.expression.ValueExpressions.TimeStampExpression;
import org.apache.drill.common.expression.ValueExpressions.VarDecimalExpression;
import org.apache.drill.common.expression.visitors.ExprVisitor;

import com.google.common.collect.Lists;

public class ConstantExpressionIdentifier implements ExprVisitor<Boolean, IdentityHashMap<LogicalExpression, Object>, RuntimeException> {

  private ConstantExpressionIdentifier() {}

  /**
   * Get a list of expressions that mark boundaries into a constant space.
   *
   * @param e expression to check for constants
   * @return list of expressions that mark boundaries into a constant space
   */
  public static Set<LogicalExpression> getConstantExpressionSet(LogicalExpression e) {
    IdentityHashMap<LogicalExpression, Object> map = new IdentityHashMap<>();
    ConstantExpressionIdentifier visitor = new ConstantExpressionIdentifier();

    if (e.accept(visitor, map) && map.isEmpty()) {
      // if we receive a constant value here but the map is empty, this means the entire tree is a constant.
      // note, we can't use a singleton collection here because we need an identity set.
      map.put(e, true);
      return map.keySet();
    } else if (map.isEmpty()) {
      // so we don't continue to carry around a map, we let it go here and simply return an empty set.
      return Collections.emptySet();
    } else {
      return map.keySet();
    }
  }

  private boolean checkChildren(LogicalExpression e, IdentityHashMap<LogicalExpression, Object> value, boolean transmitsConstant) {
    List<LogicalExpression> constants = Lists.newLinkedList();
    boolean constant = true;

    for (LogicalExpression child : e) {
      if (child.accept(this, value)) {
        constants.add(child);
      } else {
        constant = false;
      }
    }

    // if one or more clauses isn't constant, this isn't constant.  this also isn't a constant if it operates on a set.
    if (!constant || !transmitsConstant) {
      for (LogicalExpression c : constants) {
        value.put(c, true);
      }
    }
    return constant && transmitsConstant;
  }

  @Override
  public Boolean visitFunctionCall(FunctionCall call, IdentityHashMap<LogicalExpression, Object> value) {
    throw new UnsupportedOperationException("FunctionCall is not expected here. " +
      "It should have been converted to FunctionHolderExpression in materialization");
  }

  @Override
  public Boolean visitFunctionHolderExpression(FunctionHolderExpression holder, IdentityHashMap<LogicalExpression, Object> value) throws RuntimeException {
    // constant evaluation is not supported for aggregate, random or complex functions
    return checkChildren(holder, value, !holder.isAggregating() && !holder.isRandom() && !holder.getHolder().isComplexWriterFuncHolder());
  }

  @Override
  public Boolean visitBooleanOperator(BooleanOperator op, IdentityHashMap<LogicalExpression, Object> value) throws RuntimeException {
    return checkChildren(op, value, true);
  }

  @Override
  public Boolean visitIfExpression(IfExpression ifExpr, IdentityHashMap<LogicalExpression, Object> value) {
    return checkChildren(ifExpr, value, true);
  }

  @Override
  public Boolean visitSchemaPath(SchemaPath path, IdentityHashMap<LogicalExpression, Object> value) {
    return false;
  }

  @Override
  public Boolean visitIntConstant(ValueExpressions.IntExpression intExpr, IdentityHashMap<LogicalExpression, Object> value) throws RuntimeException {
    return true;
  }

  @Override
  public Boolean visitFloatConstant(ValueExpressions.FloatExpression fExpr, IdentityHashMap<LogicalExpression, Object> value) throws RuntimeException {
    return true;
  }

  @Override
  public Boolean visitLongConstant(LongExpression intExpr, IdentityHashMap<LogicalExpression, Object> value) {
    return true;
  }

  @Override
  public Boolean visitDateConstant(DateExpression intExpr, IdentityHashMap<LogicalExpression, Object> value) {
    return true;
  }

  @Override
  public Boolean visitDecimal9Constant(Decimal9Expression decExpr, IdentityHashMap<LogicalExpression, Object> value) {
    return true;
  }

  @Override
  public Boolean visitTimeConstant(TimeExpression intExpr, IdentityHashMap<LogicalExpression, Object> value) {
    return true;
  }

  @Override
  public Boolean visitDecimal18Constant(Decimal18Expression decExpr, IdentityHashMap<LogicalExpression, Object> value) {
    return true;
  }

  @Override
  public Boolean visitIntervalYearConstant(IntervalYearExpression intExpr, IdentityHashMap<LogicalExpression, Object> value) {
    return true;
  }

  @Override
  public Boolean visitDecimal28Constant(Decimal28Expression decExpr, IdentityHashMap<LogicalExpression, Object> value) {
    return true;
  }

  @Override
  public Boolean visitIntervalDayConstant(IntervalDayExpression intExpr, IdentityHashMap<LogicalExpression, Object> value) {
    return true;
  }

  @Override
  public Boolean visitTimeStampConstant(TimeStampExpression intExpr, IdentityHashMap<LogicalExpression, Object> value) {
    return true;
  }

  @Override
  public Boolean visitDecimal38Constant(Decimal38Expression decExpr, IdentityHashMap<LogicalExpression, Object> value) {
    return true;
  }

  @Override
  public Boolean visitVarDecimalConstant(VarDecimalExpression decExpr, IdentityHashMap<LogicalExpression, Object> value) {
    return true;
  }

  @Override
  public Boolean visitDoubleConstant(DoubleExpression dExpr, IdentityHashMap<LogicalExpression, Object> value) {
    return true;
  }

  @Override
  public Boolean visitBooleanConstant(BooleanExpression e, IdentityHashMap<LogicalExpression, Object> value) {
    return true;
  }

  @Override
  public Boolean visitQuotedStringConstant(QuotedString e, IdentityHashMap<LogicalExpression, Object> value) {
    return true;
  }

  @Override
  public Boolean visitCastExpression(CastExpression e, IdentityHashMap<LogicalExpression, Object> value)
      throws RuntimeException {
    return e.getInput().accept(this, value);
  }

  @Override
  public Boolean visitUnknown(LogicalExpression e, IdentityHashMap<LogicalExpression, Object> value) {
    return checkChildren(e, value, false);
  }

  @Override
  public Boolean visitNullConstant(TypedNullConstant e, IdentityHashMap<LogicalExpression, Object> value) throws RuntimeException {
    return true;
  }

  @Override
  public Boolean visitNullExpression(NullExpression e, IdentityHashMap<LogicalExpression, Object> value) throws RuntimeException {
    return true;
  }

  @Override
  public Boolean visitConvertExpression(ConvertExpression e,
      IdentityHashMap<LogicalExpression, Object> value) throws RuntimeException {
    return e.getInput().accept(this, value);
  }

  @Override
  public Boolean visitAnyValueExpression(AnyValueExpression e,
                                         IdentityHashMap<LogicalExpression, Object> value) throws RuntimeException {
    return e.getInput().accept(this, value);
  }

  @Override
  public Boolean visitParameter(ValueExpressions.ParameterExpression e, IdentityHashMap<LogicalExpression, Object> value) throws RuntimeException {
    return false;
  }

  @Override
  public Boolean visitTypedFieldExpr(TypedFieldExpr e, IdentityHashMap<LogicalExpression, Object> value) throws RuntimeException {
    return false;
  }
}