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package org.zwobble.couscous.ast.visitors;
import net.bytebuddy.ByteBuddy;
import net.bytebuddy.description.method.MethodDescription;
import net.bytebuddy.description.modifier.FieldManifestation;
import net.bytebuddy.description.modifier.Visibility;
import net.bytebuddy.description.type.TypeDescription;
import net.bytebuddy.implementation.Implementation;
import net.bytebuddy.implementation.bytecode.Duplication;
import net.bytebuddy.implementation.bytecode.StackManipulation;
import net.bytebuddy.implementation.bytecode.Throw;
import net.bytebuddy.implementation.bytecode.TypeCreation;
import net.bytebuddy.implementation.bytecode.assign.TypeCasting;
import net.bytebuddy.implementation.bytecode.member.FieldAccess;
import net.bytebuddy.implementation.bytecode.member.MethodInvocation;
import net.bytebuddy.implementation.bytecode.member.MethodReturn;
import net.bytebuddy.implementation.bytecode.member.MethodVariableAccess;
import net.bytebuddy.matcher.ElementMatchers;
import org.zwobble.couscous.ast.Node;
import org.zwobble.couscous.ast.NodeTypes;
import org.zwobble.couscous.util.ExtraIterables;
import org.zwobble.couscous.util.ExtraSets;
import org.zwobble.couscous.util.asm.Implementations;
import org.zwobble.couscous.util.asm.StackManipulationSwitch;
import org.zwobble.couscous.util.asm.TypeDescriptions;
import java.lang.reflect.Method;
import java.util.*;
import java.util.function.BiConsumer;
import java.util.function.Consumer;
import java.util.function.Function;
import static java.util.Arrays.asList;
import static org.zwobble.couscous.util.ExtraIterables.lazyMap;
import static org.zwobble.couscous.util.ExtraLists.eagerFilter;
import static org.zwobble.couscous.util.ExtraLists.eagerMap;
import static org.zwobble.couscous.util.ExtraMaps.entry;
/**
* Dynamically generate a method to dispatch methods based on node type.
*
* <p>For instance, let's say you've defined two methods in a class called {@code NodeWriter}:</p>
*
* <blockquote><pre>
* void visit(LiteralNode);
* void visit(VariableReferenceNode);
* </pre></blockquote>
*
* Calling:
*
* <blockquote><pre>
* DynamicNodeVisitor.instantiate(nodeWriter, "visit")
* </pre></blockquote>
*
* will generate a function accepting a node equivalent to:
*
* <blockquote><pre>
* switch (node.nodeType()) {
* case NodeTypes.LITERAL:
* nodeWriter.visit((LiteralNode) node);
* return;
* case NodeTypes.VARIABLE_REFERENCE:
* nodeWriter.visit((VariableReferenceNode) node);
* return;
* default;
* return;
* }
* </pre></blockquote>
*
* <p>
* {@code visit} methods are found by performing reflection on the run-time type
* of the value passed to {@code instantiate()}. To use reflection on a super-type,
* or to avoid repeating the cost of looking up the generated code for that type,
* use {@code visitor()} instead of {@code instantiate()}.
* </p>
*
* <p>
* In answer to "why not define a visitor interface instead?":
* this allows visitors to be defined over a subset of nodes,
* rather than requiring a visit method to be defined for every node.
* Further, it allows extension of the Node interface,
* making it easier to mix and match transformations that may add or remove particular node types
* (which affects which node types later stages are required to handle).
* </p>
*/
public class DynamicNodeVisitor {
private static final Map<Map.Entry<Class<?>, String>, Function<?, Consumer>> VISITOR_BUILDERS
= new HashMap<>();
public static <T> Consumer<Node> instantiate(T visitor, String methodName) {
Map.Entry<Class<?>, String> key = entry(visitor.getClass(), methodName);
Function builder = VISITOR_BUILDERS.get(key);
if (builder == null) {
builder = buildClassSupplier(visitor.getClass(), Consumer.class, methodName, MethodReturn.VOID);
VISITOR_BUILDERS.put(key, builder);
}
return (Consumer<Node>) builder.apply(visitor);
}
public static <T> BiConsumer<Node, T> visitor(Class<T> clazz) {
Set<String> methodNames = ExtraSets.copyOf(lazyMap(asList(clazz.getDeclaredMethods()), Method::getName));
if (methodNames.size() != 1) {
throw new UnsupportedOperationException("Multiple method names");
}
String methodName = methodNames.iterator().next();
Function<T, Consumer> classSupplier = buildClassSupplier(clazz, Consumer.class, methodName, MethodReturn.VOID);
return (node, visitor) -> classSupplier.apply(visitor).accept(node);
}
static <T, F> Function<T, F> buildClassSupplier(Class<T> clazz, Class<F> function, String methodName, MethodReturn methodReturn) {
Class<? extends F> visitorClass = buildClass(clazz, function, methodName, methodReturn);
try {
return new ByteBuddy()
.subclass(Function.class)
.method(ElementMatchers.isAbstract())
.intercept(Implementations.stackManipulation(target -> new StackManipulation.Compound(
TypeCreation.of(new TypeDescription.ForLoadedType(visitorClass)),
Duplication.SINGLE,
MethodVariableAccess.REFERENCE.loadOffset(1),
TypeCasting.to(new TypeDescription.ForLoadedType(clazz)),
MethodInvocation.invoke(TypeDescriptions.findConstructor(visitorClass, clazz)),
MethodReturn.REFERENCE
)))
.make()
.load(DynamicNodeVisitor.class.getClassLoader())
.getLoaded()
.newInstance();
} catch (InstantiationException | IllegalAccessException exception) {
throw new RuntimeException(exception);
}
}
private static <T, F> Class<? extends F> buildClass(Class<T> clazz, Class<F> function, String methodName, MethodReturn methodReturn) {
List<Method> visitMethods = eagerFilter(
asList(clazz.getMethods()),
method -> isVisitMethod(methodName, method)
);
Optional<Method> defaultMethod = ExtraIterables.find(
asList(clazz.getMethods()),
method ->
method.getName().equals(methodName) &&
method.getParameterCount() == 1 &&
method.getParameterTypes()[0].equals(Node.class)
);
return new ByteBuddy()
.subclass(function)
.defineField("visitor", clazz, Visibility.PRIVATE, FieldManifestation.FINAL)
.defineConstructor(Visibility.PUBLIC)
.withParameters(clazz)
.intercept(Implementations.stackManipulation(target -> new StackManipulation.Compound(
// this()
MethodVariableAccess.REFERENCE.loadOffset(0),
MethodInvocation.invoke(TypeDescriptions.findConstructor(Object.class)),
// this.visitor = visitor
MethodVariableAccess.REFERENCE.loadOffset(0),
MethodVariableAccess.REFERENCE.loadOffset(1),
FieldAccess.forField(TypeDescriptions.findField(target, "visitor")).putter(),
// return
MethodReturn.VOID
)))
.method(ElementMatchers.isAbstract())
.intercept(Implementations.stackManipulation(target -> {
MethodDescription typeMethod = TypeDescriptions.findMethod(Node.class, "nodeType");
return new StackManipulation.Compound(
MethodVariableAccess.REFERENCE.loadOffset(1),
MethodInvocation.invoke(typeMethod),
new StackManipulationSwitch(
defaultMethod
.map(defaultMethodValue ->
delegateToMethod(target, defaultMethodValue, Node.class, methodReturn))
.orElseGet(() -> new StackManipulation.Compound(
TypeCreation.of(new TypeDescription.ForLoadedType(UnsupportedOperationException.class)),
Duplication.SINGLE,
MethodInvocation.invoke(TypeDescriptions.findConstructor(UnsupportedOperationException.class)),
Throw.INSTANCE
)),
eagerMap(visitMethods, method -> {
Class<?> nodeClass = method.getParameterTypes()[0];
return StackManipulationSwitch.switchCase(
NodeTypes.forClass(nodeClass),
delegateToMethod(target, method, nodeClass, methodReturn)
);
})
)
);
}))
.make()
.load(DynamicNodeVisitor.class.getClassLoader())
.getLoaded();
}
private static StackManipulation.Compound delegateToMethod(Implementation.Target target, Method method, Class<?> nodeClass, MethodReturn methodReturn) {
return new StackManipulation.Compound(
MethodVariableAccess.REFERENCE.loadOffset(0),
FieldAccess.forField(TypeDescriptions.findField(target, "visitor")).getter(),
MethodVariableAccess.REFERENCE.loadOffset(1),
TypeCasting.to(new TypeDescription.ForLoadedType(nodeClass)),
MethodInvocation.invoke(new MethodDescription.ForLoadedMethod(method)),
methodReturn
);
}
private static boolean isVisitMethod(String methodName, Method method) {
return
method.getName().equals(methodName) &&
method.getParameterCount() == 1 &&
Node.class.isAssignableFrom(method.getParameterTypes()[0]) &&
!method.getParameterTypes()[0].equals(Node.class);
}
}
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