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Tink is a small cryptographic library that provides a safe, simple, agile and fast way to accomplish some common cryptographic tasks.
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// Copyright 2022 Google LLC
//
// 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.crypto.tink.internal;

import com.google.crypto.tink.Key;
import java.security.GeneralSecurityException;

/**
 * Create Primitive objects from {@code Key} objects of a certain kind.
 *
 * This class should eventually be in Tinks public API -- however, it might still change before
 * that.
 * Note: Before making this public, the class name should be reconsidered. (Currently the desirable
 * option "PrimitiveFactory" is unavailable because such a class already exists.)
 */
//TODO(lizatretyakova): reconsider the name before this class becomes public.
public abstract class PrimitiveConstructor {
  /**
   * A function which creates a Primitive object.
   *
   * 
This interface exists only so we have a type we can reference in {@link #create}. Users
   * should not use this directly; see the explanation in {@link #create}.
   */
  public interface PrimitiveConstructionFunction<
      KeyT extends Key, PrimitiveT> {
    PrimitiveT constructPrimitive(KeyT key) throws GeneralSecurityException;
  }

  private final Class keyClass;
  private final Class primitiveClass;

  private PrimitiveConstructor(
      Class keyClass, Class primitiveClass) {
    this.keyClass = keyClass;
    this.primitiveClass = primitiveClass;
  }

  public abstract PrimitiveT constructPrimitive(KeyT key)
      throws GeneralSecurityException;

  public Class getKeyClass() {
    return keyClass;
  }

  public Class getPrimitiveClass() {
    return primitiveClass;
  }

  /**
   * Creates a PrimitiveConstructor object.
   *
   * 
This function should only be used by Primitives authors, that is, end users should almost
   * certainly avoid using this function directly, and instead use their respective Primitive's
   * {@code register()} method.
   *
   * 
That being said, one typically creates a PrimitiveConstructor object by writing a function
   *
   * 
{@code
   * class MyClass {
   *   private static MyPrimitive getPrimitive(MyKey key)
   *             throws GeneralSecurityException {
   *     ...
   *   }
   * }
   * }
   *
   * This function can then be used to create a {@code PrimitiveConstructor}:
   *
   * {@code
   * PrimitiveConstructor serializer =
   *       PrimitiveConstructor.create(MyClass::getPrimitive, MyKey.class,
   *                                  MyPrimitive.class);
   * }
   *
   * -- and the resulting {@code PrimitiveConstructor} object can in turn be registered in a
   * {@code PrimitiveRegistry}.
   */
  public static 
  PrimitiveConstructor create(
      PrimitiveConstructionFunction function,
      Class keyClass,
      Class primitiveClass) {
    return new PrimitiveConstructor(keyClass, primitiveClass) {
      @Override
      public PrimitiveT constructPrimitive(KeyT key) throws GeneralSecurityException {
        return function.constructPrimitive(key);
      }
    };
  }
}