/*
 * Copyright (C) 2006 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.elasticsearch.common.inject;

/**
 * A scope is a level of visibility that instances provided by Guice may have.
 * By default, an instance created by the {@link Injector} has <i>no scope</i>,
 * meaning it has no state from the framework's perspective -- the
 * {@code Injector} creates it, injects it once into the class that required it,
 * and then immediately forgets it. Associating a scope with a particular
 * binding allows the created instance to be "remembered" and possibly used
 * again for other injections.
 * <p>
 * An example of a scope is {@link Scopes#SINGLETON}.
 *
 * @author crazybob@google.com (Bob Lee)
 */
public interface Scope {

    /**
     * Scopes a provider. The returned provider returns objects from this scope.
     * If an object does not exist in this scope, the provider can use the given
     * unscoped provider to retrieve one.
     * <p>
     * Scope implementations are strongly encouraged to override
     * {@link Object#toString} in the returned provider and include the backing
     * provider's {@code toString()} output.
     *
     * @param key      binding key
     * @param unscoped locates an instance when one doesn't already exist in this
     *                 scope.
     * @return a new provider which only delegates to the given unscoped provider
     *         when an instance of the requested object doesn't already exist in this
     *         scope
     */
    <T> Provider<T> scope(Key<T> key, Provider<T> unscoped);

    /**
     * A short but useful description of this scope.  For comparison, the standard
     * scopes that ship with guice use the descriptions
     * {@code "Scopes.SINGLETON"}, {@code "ServletScopes.SESSION"} and
     * {@code "ServletScopes.REQUEST"}.
     */
    @Override
    String toString();
}