path: root/sangria-contextual/src/main/java/com/tavianator/sangria/contextual/ContextSensitiveBinder.java

/****************************************************************************
 * Sangria                                                                  *
 * Copyright (C) 2014 Tavian Barnes <tavianator@tavianator.com>             *
 *                                                                          *
 * 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 com.tavianator.sangria.contextual;

import java.lang.annotation.Annotation;
import java.util.*;
import javax.inject.Inject;

import com.google.inject.AbstractModule;
import com.google.inject.Binder;
import com.google.inject.Binding;
import com.google.inject.ConfigurationException;
import com.google.inject.Injector;
import com.google.inject.Key;
import com.google.inject.Provider;
import com.google.inject.TypeLiteral;
import com.google.inject.matcher.AbstractMatcher;
import com.google.inject.matcher.Matcher;
import com.google.inject.spi.BindingTargetVisitor;
import com.google.inject.spi.Dependency;
import com.google.inject.spi.DependencyAndSource;
import com.google.inject.spi.InjectionPoint;
import com.google.inject.spi.ProviderInstanceBinding;
import com.google.inject.spi.ProviderWithExtensionVisitor;
import com.google.inject.spi.ProvisionListener;

import com.tavianator.sangria.core.DelayedError;
import com.tavianator.sangria.core.UniqueAnnotations;

/**
 * A binder for {@link ContextSensitiveProvider}s.
 *
 * <p>
 * For example, to bind a custom logger provider, you can write this inside {@link AbstractModule#configure()}:
 * </p>
 *
 * <pre>
 * ContextSensitiveBinder.create(binder())
 *         .bind(CustomLogger.class)
 *         .toContextSensitiveProvider(CustomLoggerProvider.class);
 * </pre>
 *
 * @author Tavian Barnes (tavianator@tavianator.com)
 * @version 1.0
 * @since 1.0
 */
public class ContextSensitiveBinder {
    private static final Class<?>[] SKIPPED_SOURCES = {
            ContextSensitiveBinder.class,
            BindingBuilder.class,
    };

    private final Binder binder;

    /**
     * Create a {@link ContextSensitiveBinder}.
     *
     * @param binder The {@link Binder} to use.
     * @return A {@link ContextSensitiveBinder} instance.
     */
    public static ContextSensitiveBinder create(Binder binder) {
        return new ContextSensitiveBinder(binder);
    }

    private ContextSensitiveBinder(Binder binder) {
        this.binder = binder.skipSources(SKIPPED_SOURCES);
    }

    /**
     * See the EDSL examples {@link ContextSensitiveBinder here}.
     */
    public <T> AnnotatedContextSensitiveBindingBuilder<T> bind(Class<T> type) {
        return new BindingBuilder<>(Key.get(type));
    }

    /**
     * See the EDSL examples {@link ContextSensitiveBinder here}.
     */
    public <T> AnnotatedContextSensitiveBindingBuilder<T> bind(TypeLiteral<T> type) {
        return new BindingBuilder<>(Key.get(type));
    }

    /**
     * See the EDSL examples {@link ContextSensitiveBinder here}.
     */
    public <T> ContextSensitiveBindingBuilder<T> bind(Key<T> key) {
        return new BindingBuilder<>(key);
    }

    /**
     * Fluent binding builder implementation.
     */
    private class BindingBuilder<T> implements AnnotatedContextSensitiveBindingBuilder<T> {
        private final Key<T> bindingKey;
        private final DelayedError error;

        BindingBuilder(Key<T> bindingKey) {
            this.bindingKey = bindingKey;
            this.error = DelayedError.create(binder, "Missing call to toContextSensitiveProvider() for %s", bindingKey);
        }

        @Override
        public ContextSensitiveBindingBuilder<T> annotatedWith(Class<? extends Annotation> annotationType) {
            error.cancel();
            return new BindingBuilder<>(Key.get(bindingKey.getTypeLiteral(), annotationType));
        }

        @Override
        public ContextSensitiveBindingBuilder<T> annotatedWith(Annotation annotation) {
            error.cancel();
            return new BindingBuilder<>(Key.get(bindingKey.getTypeLiteral(), annotation));
        }

        @Override
        public void toContextSensitiveProvider(Class<? extends ContextSensitiveProvider<? extends T>> type) {
            toContextSensitiveProvider(Key.get(type));
        }

        @Override
        public void toContextSensitiveProvider(TypeLiteral<? extends ContextSensitiveProvider<? extends T>> type) {
            toContextSensitiveProvider(Key.get(type));
        }

        @Override
        public void toContextSensitiveProvider(Key<? extends ContextSensitiveProvider<? extends T>> key) {
            error.cancel();

            binder.bind(bindingKey).toProvider(new ProviderKeyAdapter<>(key, makeLinkedKey(key)));
            binder.bindListener(new BindingMatcher(bindingKey), new Trigger(bindingKey));
        }

        private <U> Key<U> makeLinkedKey(Key<U> key) {
            Key<U> linkedKey = Key.get(key.getTypeLiteral(), UniqueAnnotations.create());
            binder.bind(linkedKey)
                    .to(key);
            return linkedKey;
        }

        @Override
        public void toContextSensitiveProvider(ContextSensitiveProvider<? extends T> provider) {
            error.cancel();

            binder.bind(bindingKey).toProvider(new ProviderInstanceAdapter<>(provider));
            binder.bindListener(new BindingMatcher(bindingKey), new Trigger(bindingKey));
            // Match the behaviour of LinkedBindingBuilder#toProvider(Provider)
            binder.requestInjection(provider);
        }
    }

    /**
     * Adapter from {@link ContextSensitiveProvider} to {@link Provider}.
     */
    private static abstract class ProviderAdapter<T> implements ProviderWithExtensionVisitor<T> {
        private static final ThreadLocal<InjectionPoint> CURRENT_CONTEXT = new ThreadLocal<>();

        static void pushContext(InjectionPoint ip) {
            CURRENT_CONTEXT.set(ip);
        }

        static void popContext() {
            CURRENT_CONTEXT.remove();
        }

        @Override
        public T get() {
            InjectionPoint ip = CURRENT_CONTEXT.get();
            if (ip != null) {
                return delegate().getInContext(ip);
            } else {
                return delegate().getInUnknownContext();
            }
        }

        abstract ContextSensitiveProvider<? extends T> delegate();

        // Have to implement equals()/hashCode() to support binding de-duplication
        @Override
        public abstract boolean equals(Object obj);

        @Override
        public abstract int hashCode();
    }

    private static class ProviderKeyAdapter<T> extends ProviderAdapter<T> implements ContextSensitiveProviderKeyBinding<T> {
        private final Key<? extends ContextSensitiveProvider<? extends T>> providerKey;
        private final Key<? extends ContextSensitiveProvider<? extends T>> linkedKey;
        private Provider<? extends ContextSensitiveProvider<? extends T>> provider;

        ProviderKeyAdapter(
                Key<? extends ContextSensitiveProvider<? extends T>> providerKey,
                Key<? extends ContextSensitiveProvider<? extends T>> linkedKey) {
            this.providerKey = providerKey;
            this.linkedKey = linkedKey;
        }

        @Inject
        void inject(Injector injector) {
            provider = injector.getProvider(linkedKey);
        }

        @Override
        ContextSensitiveProvider<? extends T> delegate() {
            return provider.get();
        }

        @SuppressWarnings("unchecked") // The real type of B must be T
        @Override
        public <B, V> V acceptExtensionVisitor(BindingTargetVisitor<B, V> visitor, ProviderInstanceBinding<? extends B> binding) {
            if (visitor instanceof ContextSensitiveBindingVisitor) {
                return ((ContextSensitiveBindingVisitor<T, V>)visitor).visit(this);
            } else {
                return visitor.visit(binding);
            }
        }

        @Override
        public Key<? extends ContextSensitiveProvider<? extends T>> getContextSensitiveProviderKey() {
            return providerKey;
        }

        @Override
        public boolean equals(Object obj) {
            if (obj == this) {
                return true;
            } else if (!(obj instanceof ProviderKeyAdapter)) {
                return false;
            }

            ProviderKeyAdapter<?> other = (ProviderKeyAdapter<?>)obj;
            return providerKey.equals(other.providerKey);
        }

        @Override
        public int hashCode() {
            return providerKey.hashCode();
        }
    }

    private static class ProviderInstanceAdapter<T> extends ProviderAdapter<T> implements ContextSensitiveProviderInstanceBinding<T> {
        private final ContextSensitiveProvider<? extends T> instance;
        private Set<InjectionPoint> injectionPoints;

        ProviderInstanceAdapter(ContextSensitiveProvider<? extends T> instance) {
            this.instance = instance;

            Set<InjectionPoint> injectionPoints;
            try {
                injectionPoints = InjectionPoint.forInstanceMethodsAndFields(instance.getClass());
            } catch (ConfigurationException e) {
                // We can ignore the error, the earlier requestInjection(instance) call will have reported it
                injectionPoints = e.getPartialValue();
            }
            this.injectionPoints = injectionPoints;
        }

        @Override
        ContextSensitiveProvider<? extends T> delegate() {
            return instance;
        }

        @SuppressWarnings("unchecked") // The real type of B must be T
        @Override
        public <B, V> V acceptExtensionVisitor(BindingTargetVisitor<B, V> visitor, ProviderInstanceBinding<? extends B> binding) {
            if (visitor instanceof ContextSensitiveBindingVisitor) {
                return ((ContextSensitiveBindingVisitor<T, V>)visitor).visit(this);
            } else {
                return visitor.visit(binding);
            }
        }

        @Override
        public ContextSensitiveProvider<? extends T> getContextSensitiveProviderInstance() {
            return instance;
        }

        @Override
        public Set<InjectionPoint> getInjectionPoints() {
            return injectionPoints;
        }

        @Override
        public boolean equals(Object obj) {
            if (obj == this) {
                return true;
            } else if (!(obj instanceof ProviderInstanceAdapter)) {
                return false;
            }

            ProviderInstanceAdapter<?> other = (ProviderInstanceAdapter<?>)obj;
            return instance.equals(other.instance);
        }

        @Override
        public int hashCode() {
            return instance.hashCode();
        }
    }

    /**
     * {@link Matcher} for {@link Binding}s for specific {@link Key}s.
     */
    private static class BindingMatcher extends AbstractMatcher<Binding<?>> {
        private final Key<?> key;

        BindingMatcher(Key<?> key) {
            this.key = key;
        }

        @Override
        public boolean matches(Binding<?> binding) {
            return key.equals(binding.getKey());
        }
    }

    /**
     * {@link ProvisionListener} that sets up the current {@link InjectionPoint}.
     */
    private static class Trigger implements ProvisionListener {
        private final Key<?> key;

        Trigger(Key<?> key) {
            this.key = key;
        }

        @Override
        public <T> void onProvision(ProvisionInvocation<T> provision) {
            for (DependencyAndSource dependencyAndSource : provision.getDependencyChain()) {
                Dependency<?> dependency = dependencyAndSource.getDependency();
                if (dependency != null && key.equals(dependency.getKey())) {
                    try {
                        ProviderAdapter.pushContext(dependency.getInjectionPoint());
                        provision.provision();
                    } finally {
                        ProviderAdapter.popContext();
                    }

                    break;
                }
            }
        }

        // Allow listeners to be de-duplicated
        @Override
        public boolean equals(Object obj) {
            if (obj == this) {
                return true;
            } else if (!(obj instanceof Trigger)) {
                return false;
            }

            Trigger other = (Trigger)obj;
            return key.equals(other.key);
        }

        @Override
        public int hashCode() {
            return key.hashCode();
        }
    }
}