/* Copyright 2012 Google, Inc.
*
* Licensed 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.arbeitspferde.groningen.common;
import static com.google.common.base.Preconditions.checkState;
import com.google.common.base.Objects;
import com.google.common.collect.MapMaker;
import com.google.common.collect.Maps;
import com.google.inject.Key;
import com.google.inject.OutOfScopeException;
import com.google.inject.Provider;
import javax.annotation.Nullable;
import java.util.Map;
import java.util.Map.Entry;
/**
* A simple implementation of {@link BlockScope}.
*/
public class SimpleScope implements BlockScope {
static class Memento {
private final Map<Key<?>, Object> values;
private Memento(SimpleScope scopeToCapture) {
values = scopeToCapture.isInScope() ? Maps.newHashMap(scopeToCapture.values.get()) : null;
}
@Override
public boolean equals(Object that) {
if (!(that instanceof Memento)) {
return false;
}
return Objects.equal(this.values, ((Memento) that).values);
}
@Override
public int hashCode() {
return Objects.hashCode(values);
}
}
private static final Provider<Object> SEEDED_KEY_PROVIDER =
new Provider<Object>() {
@Override
public Object get() {
throw new IllegalStateException("If you got here then it means that" +
" your code asked for scoped object which should have been" +
" explicitly seeded in this scope by calling" +
" SimpleScope.seed(), but was not.");
}
};
// Dummy value to associate with an Object in the backing Map
private static final Object PRESENT = new Object();
private static final ThreadLocal<Map<SimpleScope, Object>> ACTIVE_SCOPES =
new ThreadLocal<Map<SimpleScope, Object>>() {
@Override protected Map<SimpleScope, Object> initialValue() {
return new MapMaker().weakKeys().makeMap();
}
};
private final ThreadLocal<Map<Key<?>, Object>> values = new ThreadLocal<>();
static Map<SimpleScope, SimpleScope.Memento> captureActiveSimpleScopes() {
Map<SimpleScope, SimpleScope.Memento> simpleScopeMap = Maps.newHashMap();
for (SimpleScope simpleScope : ACTIVE_SCOPES.get().keySet()) {
simpleScopeMap.put(simpleScope, new Memento(simpleScope));
}
return simpleScopeMap;
}
static void replaceActiveSimpleScopes(Map<SimpleScope, SimpleScope.Memento> capturedScopes) {
SimpleScope.ACTIVE_SCOPES.get().clear();
for (Entry<SimpleScope, SimpleScope.Memento> simpleScopeMapEntry : capturedScopes.entrySet()) {
SimpleScope simpleScope = simpleScopeMapEntry.getKey();
SimpleScope.Memento memento = simpleScopeMapEntry.getValue();
if (memento.values == null) {
simpleScope.values.remove();
} else {
simpleScope.values.set(memento.values);
ACTIVE_SCOPES.get().put(simpleScope, PRESENT);
}
}
}
@Override
public void enter() {
checkState(!isInScope(), "A scoping block is already in progress");
values.set(Maps.<Key<?>, Object>newHashMap());
ACTIVE_SCOPES.get().put(this, PRESENT);
}
@Override
public void exit() {
checkState(isInScope(), "No scoping block in progress");
values.remove();
ACTIVE_SCOPES.get().remove(this);
}
@Override
public boolean isInScope() {
return (values.get() != null);
}
@Override
public <T> void seed(Key<T> key, @Nullable T value) {
Map<Key<?>, Object> scopedObjects = getScopedObjectMap(key);
checkState(!scopedObjects.containsKey(key), "A value for the key %s was " +
"already seeded in this scope. Old value: %s New value: %s", key,
scopedObjects.get(key), value);
scopedObjects.put(key, value);
}
@Override
public <T> void seed(Class<T> clazz, @Nullable T value) {
seed(Key.get(clazz), value);
}
@Override
public <T> Provider<T> scope(final Key<T> key, final Provider<T> unscoped) {
return new Provider<T>() {
@Override
public T get() {
Map<Key<?>, Object> scopedObjects = getScopedObjectMap(key);
@SuppressWarnings("unchecked")
T current = (T) scopedObjects.get(key);
if (current == null && !scopedObjects.containsKey(key)) {
current = unscoped.get();
scopedObjects.put(key, current);
}
return current;
}
};
}
private <T> Map<Key<?>, Object> getScopedObjectMap(Key<T> key) {
Map<Key<?>, Object> scopedObjects = values.get();
if (scopedObjects == null) {
throw new OutOfScopeException("Cannot access " + key
+ " outside of a scoping block");
}
return scopedObjects;
}
/**
* Returns a provider that always throws exception complaining that the object
* in question must be seeded before it can be injected.
*
* @return typed provider
*/
@SuppressWarnings({"unchecked"})
public static final <T> Provider<T> seededKeyProvider() {
return (Provider<T>) SEEDED_KEY_PROVIDER;
}
}