/*
 * Copyright (C) 2014 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 com.google.inject.multibindings;

import com.google.inject.Binding;
import com.google.inject.Key;
import com.google.inject.spi.Element;
import com.google.inject.spi.Elements;

A binding for a OptionalBinder.
Although OptionalBinders may be injected through a variety of types T, 
Optional<T>, Optional<Provider<T>>, etc..), an OptionalBinderBinding exists only on the Binding associated with the Optional<T> key. Other bindings can be validated to be derived from this OptionalBinderBinding using containsElement. 
Author:
sameb@google.com (Sam Berlin)
Type parameters:
<T> – The fully qualified type of the optional binding, including Optional. For example: Optional<String>.
Since:
4.0/**
 * A binding for a OptionalBinder.
 *
 * <p>Although OptionalBinders may be injected through a variety of types {@code T}, {@code
 * Optional<T>}, {@code Optional<Provider<T>>}, etc..), an OptionalBinderBinding exists only on the
 * Binding associated with the {@code Optional<T>} key. Other bindings can be validated to be
 * derived from this OptionalBinderBinding using {@link #containsElement}.
 *
 * @param <T> The fully qualified type of the optional binding, including Optional. For example:
 *     {@code Optional<String>}.
 * @since 4.0
 * @author sameb@google.com (Sam Berlin)
 */
public interface OptionalBinderBinding<T> {

  
Returns the Key for this binding. /** Returns the {@link Key} for this binding. */
  Key<T> getKey();

  
Returns the default binding (set by OptionalBinder.setDefault) if one exists or null if no default binding is set. This will throw UnsupportedOperationException if it is called on an element retrieved from Elements.getElements. 
The Binding's type will always match the type Optional's generic type. For example, if
getKey returns a key of Optional<String>, then this will always return a 
Binding<String>.
/**
   * Returns the default binding (set by {@link OptionalBinder#setDefault}) if one exists or null if
   * no default binding is set. This will throw {@link UnsupportedOperationException} if it is
   * called on an element retrieved from {@link Elements#getElements}.
   *
   * <p>The Binding's type will always match the type Optional's generic type. For example, if
   * getKey returns a key of <code>Optional&lt;String></code>, then this will always return a <code>
   * Binding&lt;String></code>.
   */
  Binding<?> getDefaultBinding();

  
Returns the actual binding (set by OptionalBinder.setBinding) or null if not set. This will throw UnsupportedOperationException if it is called on an element retrieved from Elements.getElements. 
The Binding's type will always match the type Optional's generic type. For example, if
getKey returns a key of Optional<String>, then this will always return a 
Binding<String>.
/**
   * Returns the actual binding (set by {@link OptionalBinder#setBinding}) or null if not set. This
   * will throw {@link UnsupportedOperationException} if it is called on an element retrieved from
   * {@link Elements#getElements}.
   *
   * <p>The Binding's type will always match the type Optional's generic type. For example, if
   * getKey returns a key of <code>Optional&lt;String></code>, then this will always return a <code>
   * Binding&lt;String></code>.
   */
  Binding<?> getActualBinding();

  
Returns true if this OptionalBinder contains the given Element in order to build the optional binding or uses the given Element in order to support building and injecting its data. This will work for OptionalBinderBinding retrieved from an injector and Elements.getElements. Usually this is only necessary if you are working with elements retrieved from modules (without an Injector), otherwise getDefaultBinding and getActualBinding are better options. /**
   * Returns true if this OptionalBinder contains the given Element in order to build the optional
   * binding or uses the given Element in order to support building and injecting its data. This
   * will work for OptionalBinderBinding retrieved from an injector and {@link
   * Elements#getElements}. Usually this is only necessary if you are working with elements
   * retrieved from modules (without an Injector), otherwise {@link #getDefaultBinding} and {@link
   * #getActualBinding} are better options.
   */
  boolean containsElement(Element element);
}