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The core HTTP and composition mechanisms of Ratpack
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/*
 * Copyright 2013 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.base.Predicate;
import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;
import com.google.common.collect.Lists;
import com.google.common.reflect.TypeToken;
import com.google.common.util.concurrent.UncheckedExecutionException;
import ratpack.func.Action;
import ratpack.registry.PredicateCacheability;
import ratpack.registry.Registry;

import java.util.List;
import java.util.Optional;
import java.util.concurrent.ExecutionException;

import static ratpack.util.ExceptionUtils.toException;
import static ratpack.util.ExceptionUtils.uncheck;

public class CachingRegistry implements Registry {

  private final Registry delegate;

  private final LoadingCache, ? extends Optional> cache = CacheBuilder.newBuilder().build(new CacheLoader, Optional>() {
    public Optional load(@SuppressWarnings("NullableProblems") TypeToken key) throws Exception {
      return delegate.maybeGet(key);
    }
  });

  private final LoadingCache, List> allCache = CacheBuilder.newBuilder().build(new CacheLoader, List>() {
    public List load(@SuppressWarnings("NullableProblems") TypeToken key) throws Exception {
      return Lists.newArrayList(delegate.getAll(key));
    }
  });

  private LoadingCache, List> predicateCache = CacheBuilder.newBuilder().build(new CacheLoader, List>() {
    @Override
    public List load(@SuppressWarnings("NullableProblems") PredicateCacheability.CacheKey key) throws Exception {
      return Lists.newArrayList(getAll(key));
    }

    private  Iterable getAll(PredicateCacheability.CacheKey key) {
      return delegate.all(key.type, key.predicate);
    }
  });

  public CachingRegistry(Registry delegate) {
    this.delegate = delegate;
  }

  @Override
  public  Optional maybeGet(TypeToken type) {
    try {
      @SuppressWarnings("unchecked") Optional o = (Optional) cache.get(type);
      return o;
    } catch (ExecutionException | UncheckedExecutionException e) {
      throw uncheck(toException(e.getCause()));
    }
  }

  @Override
  public  List getAll(TypeToken type) {
    try {
      @SuppressWarnings("unchecked") List objects = (List) allCache.get(type);
      return objects;
    } catch (ExecutionException | UncheckedExecutionException e) {
      throw uncheck(toException(e.getCause()));
    }
  }

  private  List getFromPredicateCache(TypeToken type, Predicate predicate) {
    try {
      @SuppressWarnings("unchecked") List objects = (List) predicateCache.get(new PredicateCacheability.CacheKey<>(type, predicate));
      return objects;
    } catch (ExecutionException | UncheckedExecutionException e) {
      throw uncheck(toException(e.getCause()));
    }
  }

  @Override
  public  Optional first(TypeToken type, Predicate predicate) {
    if (PredicateCacheability.isCacheable(predicate)) {
      List objects = getFromPredicateCache(type, predicate);
      if (objects.isEmpty()) {
        return Optional.empty();
      } else {
        return Optional.of(objects.get(0));
      }
    } else {
      return delegate.first(type, predicate);
    }
  }

  @Override
  public  Iterable all(TypeToken type, Predicate predicate) {
    if (PredicateCacheability.isCacheable(predicate)) {
      return getFromPredicateCache(type, predicate);
    } else {
      return delegate.all(type, predicate);
    }
  }

  @Override
  public  boolean each(TypeToken type, Predicate predicate, Action action) throws Exception {
    Iterable all = all(type, predicate);
    boolean any = false;
    for (T item : all) {
      any = true;
      action.execute(item);
    }

    return any;
  }

  @Override
  public String toString() {
    return "CachingRegistry{delegate=" + delegate + '}';
  }
}