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package bjc.utils.data;
import java.util.function.Function;
import java.util.function.Supplier;
import java.util.function.UnaryOperator;
import bjc.utils.funcdata.FunctionalList;
import bjc.utils.funcdata.IFunctionalList;
/**
* A holder that holds a means to create a value, but doesn't actually
* compute the value until it's needed
*
* @author ben
*
* @param <ContainedType>
*/
public class Lazy<ContainedType> implements IHolder<ContainedType> {
private Supplier<ContainedType> valueSupplier;
private IFunctionalList<UnaryOperator<ContainedType>> actions = new FunctionalList<>();
private boolean valueMaterialized;
private ContainedType heldValue;
/**
* Create a new lazy value from the specified seed value
*
* @param value
* The seed value to use
*/
public Lazy(ContainedType value) {
heldValue = value;
valueMaterialized = true;
}
/**
* Create a new lazy value from the specified value source
*
* @param supp
* The source of a value to use
*/
public Lazy(Supplier<ContainedType> supp) {
valueSupplier = supp;
valueMaterialized = false;
}
private Lazy(Supplier<ContainedType> supp,
IFunctionalList<UnaryOperator<ContainedType>> pendingActions) {
valueSupplier = supp;
actions = pendingActions;
}
@Override
public <BoundType> IHolder<BoundType> bind(
Function<ContainedType, IHolder<BoundType>> binder) {
IFunctionalList<UnaryOperator<ContainedType>> pendingActions = new FunctionalList<>();
actions.forEach(pendingActions::add);
Supplier<ContainedType> supplier = () -> {
if (valueMaterialized) {
return heldValue;
}
return valueSupplier.get();
};
return new BoundLazy<>(() -> {
return new Lazy<>(supplier, pendingActions);
}, binder);
}
@Override
public <MappedType> IHolder<MappedType> map(
Function<ContainedType, MappedType> mapper) {
IFunctionalList<UnaryOperator<ContainedType>> pendingActions = new FunctionalList<>();
actions.forEach(pendingActions::add);
return new Lazy<>(() -> {
ContainedType currVal = heldValue;
if (!valueMaterialized) {
currVal = valueSupplier.get();
}
return pendingActions.reduceAux(currVal,
UnaryOperator<ContainedType>::apply,
(value) -> mapper.apply(value));
});
}
@Override
public String toString() {
if (valueMaterialized) {
if (actions.isEmpty()) {
return "value[v='" + heldValue + "']";
}
return "value[v='" + heldValue + "'] (has pending transforms)";
}
return "(unmaterialized)";
}
@Override
public IHolder<ContainedType> transform(
UnaryOperator<ContainedType> transformer) {
actions.add(transformer);
return this;
}
@Override
public <UnwrappedType> UnwrappedType unwrap(
Function<ContainedType, UnwrappedType> unwrapper) {
if (!valueMaterialized) {
heldValue = valueSupplier.get();
valueMaterialized = true;
}
actions.forEach((action) -> {
heldValue = action.apply(heldValue);
});
actions = new FunctionalList<>();
return unwrapper.apply(heldValue);
}
}
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