package uk.ac.imperial.lsds.streamsql.expressions;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import uk.ac.imperial.lsds.seep.comm.serialization.DataTuple;
import uk.ac.imperial.lsds.streamsql.conversion.NumericConversion;
import uk.ac.imperial.lsds.streamsql.conversion.TypeConversion;
import uk.ac.imperial.lsds.streamsql.util.Util;
import uk.ac.imperial.lsds.streamsql.visitors.ValueExpressionVisitor;
/*
* This class implements Subtraction between any Number type (Integer, Double, Long, etc.).
* It convert all the value to double, and then return the final result by automatic casting
* (i.e. (int) 1.0 )
*
* Double can store integers exatly in binary representation,
* so we won't lose the precision on our integer operations.
*
* Having different T types in the constructor arguments
* does not result in exception in the constructor,
* but rather in eval method.
*
* The formula applied on value expressions is: VE1 - VE2 - VE3 - ...
*/
public class Subtraction<T extends Number & Comparable<T>> implements IValueExpression<T> {
private static final long serialVersionUID = 1L;
private final List<IValueExpression> _veList = new ArrayList<IValueExpression>();
private final NumericConversion<T> _wrapper;
public Subtraction(IValueExpression ve1, IValueExpression ve2, IValueExpression... veArray) {
_veList.add(ve1);
_veList.add(ve2);
_veList.addAll(Arrays.asList(veArray));
_wrapper = (NumericConversion<T>) Util.getDominantNumericType(_veList);
}
@Override
public void accept(ValueExpressionVisitor vev) {
vev.visit(this);
}
@Override
public void changeValues(int i, IValueExpression<T> newExpr) {
_veList.remove(i);
_veList.add(i, newExpr);
}
@Override
public T eval(DataTuple tuple) {
final IValueExpression firstVE = _veList.get(0);
final Object firstObj = firstVE.eval(tuple);
final NumericConversion firstType = (NumericConversion) firstVE.getType();
double result = firstType.toDouble(firstObj);
for (int i = 1; i < _veList.size(); i++) {
final IValueExpression currentVE = _veList.get(i);
final Object currentObj = currentVE.eval(tuple);
final NumericConversion currentType = (NumericConversion) currentVE.getType();
result -= currentType.toDouble(currentObj);
}
return _wrapper.fromDouble(result);
}
@Override
public String evalString(DataTuple tuple) {
final T result = eval(tuple);
return _wrapper.toString(result);
}
@Override
public List<IValueExpression> getInnerExpressions() {
return _veList;
}
@Override
public TypeConversion getType() {
return _wrapper;
}
@Override
public void inverseNumber() {
}
@Override
public boolean isNegative() {
return false;
}
@Override
public String toString() {
final StringBuilder sb = new StringBuilder();
for (int i = 0; i < _veList.size(); i++) {
sb.append("(").append(_veList.get(i)).append(")");
if (i != _veList.size() - 1)
sb.append(" - ");
}
return sb.toString();
}
}