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package com.google.inject.spi;

import com.google.inject.Binder;
import com.google.inject.MembersInjector;
import com.google.inject.TypeLiteral;

import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;

/**
 * A lookup of the members injector for a type. Lookups are created explicitly in a module using
 * {@link com.google.inject.Binder#getMembersInjector(Class) getMembersInjector()} statements:
 *  *     MembersInjector<PaymentService> membersInjector
 *         = getMembersInjector(PaymentService.class);
 *
 */
public final class MembersInjectorLookup implements Element {

    private final Object source;
    private final TypeLiteral type;
    private MembersInjector delegate;

    public MembersInjectorLookup(Object source, TypeLiteral type) {
        this.source = checkNotNull(source, "source");
        this.type = checkNotNull(type, "type");
    }

    public Object getSource() {
        return source;
    }

    /**
     * Gets the type containing the members to be injected.
     */
    public TypeLiteral getType() {
        return type;
    }

    public  T acceptVisitor(ElementVisitor visitor) {
        return visitor.visit(this);
    }

    /**
     * Sets the actual members injector.
     *
     * @throws IllegalStateException if the delegate is already set
     */
    public void initializeDelegate(MembersInjector delegate) {
        checkState(this.delegate == null, "delegate already initialized");
        this.delegate = checkNotNull(delegate, "delegate");
    }

    public void applyTo(Binder binder) {
        initializeDelegate(binder.withSource(getSource()).getMembersInjector(type));
    }

    /**
     * Returns the delegate members injector, or {@code null} if it has not yet been initialized.
     * The delegate will be initialized when this element is processed, or otherwise used to create
     * an injector.
     */
    public MembersInjector getDelegate() {
        return delegate;
    }

    /**
     * Returns the looked up members injector. The result is not valid until this lookup has been
     * initialized, which usually happens when the injector is created. The members injector will
     * throw an {@code IllegalStateException} if you try to use it beforehand.
     */
    public MembersInjector getMembersInjector() {
        return new MembersInjector() {
            public void injectMembers(T instance) {
                checkState(delegate != null,
                        "This MembersInjector cannot be used until the Injector has been created.");
                delegate.injectMembers(instance);
            }

            @Override
            public String toString() {
                return "MembersInjector<" + type + ">";
            }
        };
    }
}