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// Copyright 2017 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.searchlib.rankingexpression.rule;
import com.google.common.collect.ImmutableList;
import com.yahoo.searchlib.rankingexpression.evaluation.Context;
import com.yahoo.searchlib.rankingexpression.evaluation.Value;
import java.util.*;
/**
* A binary mathematical operation
*
* @author bratseth
*/
public final class ArithmeticNode extends CompositeNode {
private final ImmutableList<ExpressionNode> children;
private final ImmutableList<ArithmeticOperator> operators;
public ArithmeticNode(List<ExpressionNode> children, List<ArithmeticOperator> operators) {
this.children = ImmutableList.copyOf(children);
this.operators = ImmutableList.copyOf(operators);
}
public ArithmeticNode(ExpressionNode leftExpression, ArithmeticOperator operator, ExpressionNode rightExpression) {
this.children = ImmutableList.of(leftExpression, rightExpression);
this.operators = ImmutableList.of(operator);
}
public List<ArithmeticOperator> operators() { return operators; }
@Override
public List<ExpressionNode> children() { return children; }
@Override
public String toString(SerializationContext context, Deque<String> path, CompositeNode parent) {
StringBuilder string = new StringBuilder();
boolean nonDefaultPrecedence = nonDefaultPrecedence(parent);
if (nonDefaultPrecedence)
string.append("(");
Iterator<ExpressionNode> child = children.iterator();
string.append(child.next().toString(context, path, this)).append(" ");
for (Iterator<ArithmeticOperator> op = operators.iterator(); op.hasNext() && child.hasNext();) {
string.append(op.next().toString()).append(" ");
string.append(child.next().toString(context, path, this));
if (op.hasNext())
string.append(" ");
}
if (nonDefaultPrecedence)
string.append(")");
string.append(" ");
return string.toString().trim();
}
/**
* Returns true if this node has lower precedence than the parent
* (even though by virtue of being a node it will be calculated before the parent).
*/
private boolean nonDefaultPrecedence(CompositeNode parent) {
if ( parent==null) return false;
if ( ! (parent instanceof ArithmeticNode)) return false;
ArithmeticNode arithParent = (ArithmeticNode) parent;
// The line below can only be correct in both only have one operator.
// Getting this correct is impossible without more work.
// So for now now we only handle the simple case correctly, and use a safe approach by adding
// extra parenthesis just in case....
return arithParent.operators.get(0).hasPrecedenceOver(this.operators.get(0))
|| ((arithParent.operators.size() > 1) || (operators.size() > 1));
}
@Override
public Value evaluate(Context context) {
Iterator<ExpressionNode> child = children.iterator();
Deque<ValueItem> stack = new ArrayDeque<>();
stack.push(new ValueItem(ArithmeticOperator.PLUS, child.next().evaluate(context)));
for (Iterator<ArithmeticOperator> it = operators.iterator(); it.hasNext() && child.hasNext();) {
ArithmeticOperator op = it.next();
if (!stack.isEmpty()) {
while (stack.peek().op.hasPrecedenceOver(op)) {
popStack(stack);
}
}
stack.push(new ValueItem(op, child.next().evaluate(context)));
}
while (stack.size() > 1) {
popStack(stack);
}
return stack.getFirst().value;
}
private void popStack(Deque<ValueItem> stack) {
ValueItem rhs = stack.pop();
ValueItem lhs = stack.peek();
lhs.value = rhs.op.evaluate(lhs.value, rhs.value);
}
public static ArithmeticNode resolve(ExpressionNode left, ArithmeticOperator op, ExpressionNode right) {
if ( ! (left instanceof ArithmeticNode)) return new ArithmeticNode(left, op, right);
ArithmeticNode leftArithmetic = (ArithmeticNode)left;
List<ExpressionNode> newChildren = new ArrayList<>(leftArithmetic.children());
newChildren.add(right);
List<ArithmeticOperator> newOperators = new ArrayList<>(leftArithmetic.operators());
newOperators.add(op);
return new ArithmeticNode(newChildren, newOperators);
}
private static class ValueItem {
final ArithmeticOperator op;
Value value;
public ValueItem(ArithmeticOperator op, Value value) {
this.op = op;
this.value = value;
}
}
@Override
public CompositeNode setChildren(List<ExpressionNode> newChildren) {
if (children.size() != newChildren.size())
throw new IllegalArgumentException("Expected " + children.size() + " children but got " + newChildren.size());
return new ArithmeticNode(newChildren, operators);
}
}
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