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package com.google.inject;

import com.google.inject.internal.CircularDependencyProxy;
import com.google.inject.internal.LinkedBindingImpl;
import com.google.inject.internal.SingletonScope;
import com.google.inject.spi.BindingScopingVisitor;
import com.google.inject.spi.ExposedBinding;

import java.lang.annotation.Annotation;

/**
 * Built-in scope implementations.
 */
public class Scopes {

    /**
     * One instance per {@link Injector}. Also see {@code @}{@link Singleton}.
     */
    public static final Scope SINGLETON = new SingletonScope();
    /**
     * No scope; the same as not applying any scope at all.  Each time the
     * Injector obtains an instance of an object with "no scope", it injects this
     * instance then immediately forgets it.  When the next request for the same
     * binding arrives it will need to obtain the instance over again.
     *
     * This exists only in case a class has been annotated with a scope
     * annotation such as {@link Singleton @Singleton}, and you need to override
     * this to "no scope" in your binding.
     */
    public static final Scope NO_SCOPE = new Scope() {
        @Override
        public  Provider scope(Key key, Provider unscoped) {
            return unscoped;
        }

        @Override
        public String toString() {
            return "Scopes.NO_SCOPE";
        }
    };

    private static final BindingScopingVisitor IS_SINGLETON_VISITOR
            = new BindingScopingVisitor<>() {
        @Override
        public Boolean visitNoScoping() {
            return false;
        }

        @Override
        public Boolean visitScopeAnnotation(Class scopeAnnotation) {
            return scopeAnnotation == Singleton.class
                    || scopeAnnotation == javax.inject.Singleton.class;
        }

        @Override
        public Boolean visitScope(Scope scope) {
            return scope == Scopes.SINGLETON;
        }

        @Override
        public Boolean visitEagerSingleton() {
            return true;
        }
    };

    private Scopes() {
    }

    /**
     * Returns true if {@code binding} is singleton-scoped. If the binding is a {@link
     * com.google.inject.spi.LinkedKeyBinding linked key binding} and belongs to an injector (ie. it
     * was retrieved via {@link Injector#getBinding Injector.getBinding()}), then this method will
     * also true if the target binding is singleton-scoped.
     */
    public static boolean isSingleton(Binding binding) {
        do {
            boolean singleton = binding.acceptScopingVisitor(IS_SINGLETON_VISITOR);
            if (singleton) {
                return true;
            }

            if (binding instanceof LinkedBindingImpl) {
                LinkedBindingImpl linkedBinding = (LinkedBindingImpl) binding;
                Injector injector = linkedBinding.getInjector();
                if (injector != null) {
                    binding = injector.getBinding(linkedBinding.getLinkedKey());
                    continue;
                }
            } else if (binding instanceof ExposedBinding) {
                ExposedBinding exposedBinding = (ExposedBinding) binding;
                Injector injector = exposedBinding.getPrivateElements().getInjector();
                if (injector != null) {
                    binding = injector.getBinding(exposedBinding.getKey());
                    continue;
                }
            }

            return false;
        } while (true);
    }

    /**
     * Returns true if {@code binding} has the given scope. If the binding is a {@link
     * com.google.inject.spi.LinkedKeyBinding linked key binding} and belongs to an injector (ie. it
     * was retrieved via {@link Injector#getBinding Injector.getBinding()}), then this method will
     * also true if the target binding has the given scope.
     *
     * @param binding         binding to check
     * @param scope           scope implementation instance
     * @param scopeAnnotation scope annotation class
     */
    public static boolean isScoped(Binding binding, final Scope scope,
                                   final Class scopeAnnotation) {
        do {
            boolean matches = binding.acceptScopingVisitor(new BindingScopingVisitor() {
                @Override
                public Boolean visitNoScoping() {
                    return false;
                }

                @Override
                public Boolean visitScopeAnnotation(Class visitedAnnotation) {
                    return visitedAnnotation == scopeAnnotation;
                }

                @Override
                public Boolean visitScope(Scope visitedScope) {
                    return visitedScope == scope;
                }

                @Override
                public Boolean visitEagerSingleton() {
                    return false;
                }
            });

            if (matches) {
                return true;
            }

            if (binding instanceof LinkedBindingImpl) {
                LinkedBindingImpl linkedBinding = (LinkedBindingImpl) binding;
                Injector injector = linkedBinding.getInjector();
                if (injector != null) {
                    binding = injector.getBinding(linkedBinding.getLinkedKey());
                    continue;
                }
            } else if (binding instanceof ExposedBinding) {
                ExposedBinding exposedBinding = (ExposedBinding) binding;
                Injector injector = exposedBinding.getPrivateElements().getInjector();
                if (injector != null) {
                    binding = injector.getBinding(exposedBinding.getKey());
                    continue;
                }
            }

            return false;
        } while (true);
    }

    /**
     * Returns true if the object is a proxy for a circular dependency,
     * constructed by Guice because it encountered a circular dependency. Scope
     * implementations should be careful to not cache circular proxies,
     * because the proxies are not intended for general purpose use. (They are
     * designed just to fulfill the immediate injection, not all injections.
     * Caching them can lead to IllegalArgumentExceptions or ClassCastExceptions.)
     */
    public static boolean isCircularProxy(Object object) {
        return object instanceof CircularDependencyProxy;
    }
}