/*
 * Copyright (C) 2008 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.internal;

import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.Maps;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;

/**
 * Lazily creates (and caches) values for keys. If creating the value fails (with errors), an
 * exception is thrown on retrieval.
 *
 * @author jessewilson@google.com (Jesse Wilson)
 */
public abstract class FailableCache<K, V> {

  private final Set<K> loadingSet = ConcurrentHashMap.newKeySet();

  private final LoadingCache<K, Object> delegate =
      CacheBuilder.newBuilder()
          .build(
              new CacheLoader<K, Object>() {
                @Override
                public Object load(K key) {
                  loadingSet.add(key);
                  Errors errors = new Errors();
                  V result = null;
                  try {
                    result = FailableCache.this.create(key, errors);
                  } catch (ErrorsException e) {
                    errors.merge(e.getErrors());
                  } finally {
                    loadingSet.remove(key);
                  }
                  return errors.hasErrors() ? errors : result;
                }
              });

  protected abstract V create(K key, Errors errors) throws ErrorsException;

  public V get(K key, Errors errors) throws ErrorsException {
    Object resultOrError = delegate.getUnchecked(key);
    if (resultOrError instanceof Errors) {
      errors.merge((Errors) resultOrError);
      throw errors.toException();
    } else {
      @SuppressWarnings("unchecked") // create returned a non-error result, so this is safe
      V result = (V) resultOrError;
      return result;
    }
  }

  boolean remove(K key) {
    return delegate.asMap().remove(key) != null;
  }

  boolean isLoading(K key) {
    return loadingSet.contains(key);
  }

  Map<K, V> asMap() {
    return Maps.transformValues(
        Maps.filterValues(
            ImmutableMap.copyOf(delegate.asMap()),
            resultOrError -> !(resultOrError instanceof Errors)),
        resultOrError -> {
          @SuppressWarnings("unchecked") // create returned a non-error result, so this is safe
          V result = (V) resultOrError;
          return result;
        });
  }
}
