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/* *********************************************************************
 * This Original Work is copyright of 51 Degrees Mobile Experts Limited.
 * Copyright 2019 51 Degrees Mobile Experts Limited, 5 Charlotte Close,
 * Caversham, Reading, Berkshire, United Kingdom RG4 7BY.
 *
 * This Original Work is licensed under the European Union Public Licence (EUPL) 
 * v.1.2 and is subject to its terms as set out below.
 *
 * If a copy of the EUPL was not distributed with this file, You can obtain
 * one at https://opensource.org/licenses/EUPL-1.2.
 *
 * The 'Compatible Licences' set out in the Appendix to the EUPL (as may be
 * amended by the European Commission) shall be deemed incompatible for
 * the purposes of the Work and the provisions of the compatibility
 * clause in Article 5 of the EUPL shall not apply.
 * 
 * If using the Work as, or as part of, a network application, by 
 * including the attribution notice(s) required under Article 5 of the EUPL
 * in the end user terms of the application under an appropriate heading, 
 * such notice(s) shall fulfill the requirements of that article.
 * ********************************************************************* */

package fiftyone.caching;

import java.io.IOException;

public class LruLoadingCache extends LruCacheBase implements LoadingCache {

    private ValueLoader loader;

    LruLoadingCache(int cacheSize) {
        super(cacheSize, Runtime.getRuntime().availableProcessors(), false);
    }

    LruLoadingCache(int cacheSize, int concurrency) {
        super(cacheSize, concurrency, false);
    }

    public LruLoadingCache(int cacheSize, ValueLoader loader) {
        this(cacheSize, loader, Runtime.getRuntime().availableProcessors());
    }

    LruLoadingCache(int cacheSize, ValueLoader loader, int concurrency) {
        super(cacheSize, concurrency, false);
        setCacheLoader(loader);
    }

    /**
     * Loader used to fetch items not in the cache.
     */
    public void setCacheLoader(ValueLoader loader) {
        this.loader = loader;
    }

    /**
     * Retrieves the value for key requested. If the key does not exist
     * in the cache then the Fetch method of the cache's loader is used to
     * retrieve the value.
     *
     * @param key or the item required.
     * @return An instance of the value associated with the key.
     * @throws java.lang.IllegalStateException if there was a problem accessing data file.
     */
    @Override
    public V get(K key) {
        try {
            return get(key, loader);
        } catch (IOException e) {
            throw new IllegalStateException(e);
        }
    }


    /**
     * Retrieves the value for key requested. If the key does not exist
     * in the cache then the Fetch method is used to retrieve the value
     * from another loader.
     *
     * @param key    or the item required
     * @param loader to fetch the items from
     * @return An instance of the value associated with the key
     * @throws java.io.IOException if there was a problem accessing data file.
     */
    public V get(K key, ValueLoader loader) throws IOException {
        boolean added = false;
        V result = super.get(key);

        if (result == null) {
            result = loader.load(key);
            super.add(key, result);
        }
        return result;
    }

    public static class Builder implements LoadingCacheBuilder {

        @Override
        public  Cache build(Cache c, int cacheSize) {
            return new LruLoadingCache(cacheSize);
        }
    }
}