/*
    * Licensed to the Apache Software Foundation (ASF) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * The ASF licenses this file to You 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.apache.commons.lang3.reflect;
  
  import java.lang.reflect.Type;
  import java.lang.reflect.TypeVariable;
  
  import org.apache.commons.lang3.Validate;
  
  /**
   * Type literal comparable to {@code javax.enterprise.util.TypeLiteral},
   * made generally available outside the JEE context. Allows the passing around of
   * a "token" that represents a type in a typesafe manner, as opposed to
   * passing the (non-parameterized) {@link Type} object itself. Consider:
   * <p>
   * You might see such a typesafe API as:
   * <pre>
   * class Typesafe {
   *   &lt;T&gt; T obtain(Class&lt;T&gt; type, ...);
   * }
   * </pre>
   * Consumed in the manner of:
   * <pre>
   * Foo foo = typesafe.obtain(Foo.class, ...);
   * </pre>
   * Yet, you run into problems when you want to do this with a parameterized type:
   * <pre>
   * List&lt;String&gt; listOfString = typesafe.obtain(List.class, ...); // could only give us a raw List
   * </pre>
   * {@code java.lang.reflect.Type} might provide some value:
   * <pre>
   * Type listOfStringType = ...; // firstly, how to obtain this? Doable, but not straightforward.
   * List&lt;String&gt; listOfString = (List&lt;String&gt;) typesafe.obtain(listOfStringType, ...); // nongeneric Type would necessitate a cast
   * </pre>
   * The "type literal" concept was introduced to provide an alternative, i.e.:
   * <pre>
   * class Typesafe {
   *   &lt;T&gt; T obtain(TypeLiteral&lt;T&gt; type, ...);
   * }
   * </pre>
   * Consuming code looks like:
   * <pre>
   * List&lt;String&gt; listOfString = typesafe.obtain(new TypeLiteral&lt;List&lt;String&gt;&gt;() {}, ...);
   * </pre>
   * <p>
   * This has the effect of "jumping up" a level to tie a {@code java.lang.reflect.Type}
   * to a type variable while simultaneously making it short work to obtain a
   * {@link Type} instance for any given type, inline.
   * </p>
   * <p>Additionally {@link TypeLiteral} implements the {@link Typed} interface which
   * is a generalization of this concept, and which may be implemented in custom classes.
   * It is suggested that APIs be defined in terms of the interface, in the following manner:
   * </p>
   * <pre>
   *   &lt;T&gt; T obtain(Typed&lt;T&gt; typed, ...);
   * </pre>
   *
   * @param <T> the type
   * @since 3.2
   */
  public abstract class TypeLiteral<T> implements Typed<T> {
  
      @SuppressWarnings("rawtypes")
      private static final TypeVariable<Class<TypeLiteral>> T = TypeLiteral.class.getTypeParameters()[0];
  
      /**
       * Represented type.
       */
      public final Type value;
  
      private final String toString;
  
      /**
       * The default constructor.
       */
      protected TypeLiteral() {
          this.value =
              Validate.notNull(TypeUtils.getTypeArguments(getClass(), TypeLiteral.class).get(T),
                  "%s does not assign type parameter %s", getClass(), TypeUtils.toLongString(T));
  
          this.toString = String.format("%s<%s>", TypeLiteral.class.getSimpleName(), TypeUtils.toString(value));
      }
  
      @Override
      public final boolean equals(final Object obj) {
         if (obj == this) {
             return true;
         }
         if (!(obj instanceof TypeLiteral)) {
             return false;
         }
         final TypeLiteral<?> other = (TypeLiteral<?>) obj;
         return TypeUtils.equals(value, other.value);
     }
 
     @Override
     public Type getType() {
         return value;
     }
 
     @Override
     public int hashCode() {
         return 37 << 4 | value.hashCode();
     }
 
     @Override
     public String toString() {
         return toString;
     }
 }