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The core HTTP and composition mechanisms of Ratpack
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/*
 * Copyright 2015 the original author or authors.
 *
 * 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 ratpack.registry.internal;

import com.google.common.reflect.TypeToken;
import ratpack.server.internal.ServerEnvironment;

import java.lang.reflect.Type;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.function.Function;

public abstract class TypeCaching {

  private static class Impl {

    ConcurrentMap, Boolean> cache(TypeToken left) {
      return null;
    }

    boolean isAssignableFrom(ConcurrentMap, Boolean> cache, TypeToken left, TypeToken right) {
      return isAssignableFrom(left, right);
    }

    private static boolean isAssignableFrom(TypeToken left, TypeToken right) {
      return left.equals(right) || left.isSupertypeOf(right);
    }

    @SuppressWarnings("unchecked")
     TypeToken typeToken(Type type) {
      return (TypeToken) TypeToken.of(type);
    }
  }

  private static class CachingImpl extends Impl {

    private final ConcurrentMap, ConcurrentMap, Boolean>> assignabilityCache = new ConcurrentHashMap<>();
    private final Function, ConcurrentMap, Boolean>> assignabilityIndexProducer = t -> new ConcurrentHashMap<>();

    private final ConcurrentMap> typeTokensCache = new ConcurrentHashMap<>();
    private final Function> typeTokenProducer = TypeToken::of;

    @Override
    ConcurrentMap, Boolean> cache(TypeToken left) {
      ConcurrentMap, Boolean> forLeft = assignabilityCache.get(left);
      if (forLeft == null) {
        forLeft = assignabilityCache.computeIfAbsent(left, assignabilityIndexProducer);
      }
      return forLeft;
    }

    @Override
    boolean isAssignableFrom(ConcurrentMap, Boolean> forLeft, TypeToken left, TypeToken right) {
      Boolean value = forLeft.get(right);
      if (value == null) {
        value = Impl.isAssignableFrom(left, right);
        forLeft.put(right, value);
      }
      return value;
    }

    @SuppressWarnings("unchecked")
    @Override
     TypeToken typeToken(Type type) {
      TypeToken typeToken = typeTokensCache.get(type);
      if (typeToken == null) {
        return (TypeToken) typeTokensCache.computeIfAbsent(type, typeTokenProducer);
      } else {
        return (TypeToken) typeToken;
      }
    }
  }

  private static final Impl IMPL = ServerEnvironment.INSTANCE.isDevelopment() ? new Impl() : new CachingImpl();

  public static ConcurrentMap, Boolean> cache(TypeToken left) {
    return IMPL.cache(left);
  }

  public static boolean isAssignableFrom(ConcurrentMap, Boolean> cache, TypeToken left, TypeToken right) {
    return IMPL.isAssignableFrom(cache, left, right);
  }

  public static  TypeToken typeToken(Type type) {
    return IMPL.typeToken(type);
  }

  public static  TypeToken typeToken(TypeToken type) {
    return IMPL.typeToken(type.getType());
  }

}