/**
 * Copyright (c) 2011, The University of Southampton and the individual contributors.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 *   *  Redistributions of source code must retain the above copyright notice,
 *      this list of conditions and the following disclaimer.
 *
 *   *  Redistributions in binary form must reproduce the above copyright notice,
 *      this list of conditions and the following disclaimer in the documentation
 *      and/or other materials provided with the distribution.
 *
 *   *  Neither the name of the University of Southampton nor the names of its
 *      contributors may be used to endorse or promote products derived from this
 *      software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package org.openimaj.feature;

import java.io.File;
import java.io.IOException;

import org.apache.log4j.Logger;
import org.openimaj.data.identity.Identifiable;
import org.openimaj.io.IOUtils;
import org.openimaj.io.WriteableBinary;

/**
 * A simple wrapper for a feature extractor that caches the extracted feature to
 * disk. If a feature has already been generated for a given object, it will be
 * re-read from disk rather than being re-generated.
 *
 * @author Jonathon Hare (jsh2@ecs.soton.ac.uk)
 *
 * @param <FEATURE>
 *            Type of feature
 * @param <OBJECT>
 *            Type of object
 */
public class DiskCachingFeatureExtractor<FEATURE, OBJECT extends Identifiable>
                implements
                FeatureExtractor<FEATURE, OBJECT>
{
        private static Logger logger = Logger.getLogger(DiskCachingFeatureExtractor.class);

        private File cacheDir;
        private FeatureExtractor<FEATURE, OBJECT> extractor;
        private boolean force;

        /**
         * Construct the cache in the given directory. There will be one file
         * created per object. The given extractor will be used to generate the
         * features.
         *
         * @param cacheDir
         *            the location of the cache
         * @param extractor
         *            the feature extractor
         */
        public DiskCachingFeatureExtractor(File cacheDir, FeatureExtractor<FEATURE, OBJECT> extractor) {
                this(cacheDir, extractor, false);
        }

        /**
         * Construct the cache in the given directory. There will be one file
         * created per object. The given extractor will be used to generate the
         * features. Optionally, all features can be regenerated.
         *
         * @param cacheDir
         *            the location of the cache
         * @param extractor
         *            the feature extractor
         * @param force
         *            if true, then all features will be regenerated and saved,
         *            rather than being loaded.
         */
        public DiskCachingFeatureExtractor(File cacheDir, FeatureExtractor<FEATURE, OBJECT> extractor, boolean force) {
                this.cacheDir = cacheDir;
                this.extractor = extractor;
                this.force = force;

                this.cacheDir.mkdirs();
        }

        @Override
        public FEATURE extractFeature(OBJECT object) {
                final File cachedFeature = new File(cacheDir, object.getID() + ".dat");
                cachedFeature.getParentFile().mkdirs();

                FEATURE feature = null;
                if (!force && cachedFeature.exists()) {
                        feature = load(cachedFeature);

                        if (feature != null)
                                return feature;
                }

                feature = extractor.extractFeature(object);

                try {
                        return write(feature, cachedFeature);
                } catch (final IOException e) {
                        logger.warn("Caching of the feature for the " + object.getID() + " object was disabled", e);
                        return feature;
                }
        }

        private FEATURE write(FEATURE feature, File cachedFeature) throws IOException {
                if (feature instanceof WriteableBinary) {
                        IOUtils.writeBinaryFull(cachedFeature, (WriteableBinary) feature);
                } else {
                        IOUtils.writeToFile(feature, cachedFeature);
                }

                return feature;
        }

        @SuppressWarnings("unchecked")
        private FEATURE load(File cachedFeature) {
                try {
                        return (FEATURE) IOUtils.read(cachedFeature);
                } catch (final Exception e) {
                        try {
                                return (FEATURE) IOUtils.readFromFile(cachedFeature);
                        } catch (final IOException e1) {
                                logger.warn("Error reading from cache. Feature will be regenerated.");
                        }
                }

                return null;
        }

        @Override
        public String toString() {
                return this.extractor.toString();
        }
}