/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.
 */

/* $Id$ */

package org.apache.xmlgraphics.image.loader.pipeline;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.Collections;
import java.util.List;
import java.util.Map;

import org.apache.commons.io.IOUtils;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.apache.xmlgraphics.image.loader.Image;
import org.apache.xmlgraphics.image.loader.ImageException;
import org.apache.xmlgraphics.image.loader.ImageFlavor;
import org.apache.xmlgraphics.image.loader.ImageInfo;
import org.apache.xmlgraphics.image.loader.ImageSessionContext;
import org.apache.xmlgraphics.image.loader.cache.ImageCache;
import org.apache.xmlgraphics.image.loader.impl.ImageRawStream;
import org.apache.xmlgraphics.image.loader.spi.ImageConverter;
import org.apache.xmlgraphics.image.loader.spi.ImageImplRegistry;
import org.apache.xmlgraphics.image.loader.spi.ImageLoader;
import org.apache.xmlgraphics.image.loader.util.Penalty;

/**
 * Represents a pipeline of ImageConverters with an ImageLoader at the beginning of the
 * pipeline.
 */
public class ImageProviderPipeline {

    /** logger */
    protected static final Log log = LogFactory.getLog(ImageProviderPipeline.class);

    private ImageCache cache;
    private ImageLoader loader;
    private List converters = new java.util.ArrayList();

    /**
     * Main constructor.
     * @param cache the image cache (may be null if no caching is desired)
     * @param loader the image loader to drive the pipeline with
     */
    public ImageProviderPipeline(ImageCache cache, ImageLoader loader) {
        this.cache = cache;
        setImageLoader(loader);
    }

    /**
     * Constructor for operation without caching.
     * @param loader the image loader to drive the pipeline with
     */
    public ImageProviderPipeline(ImageLoader loader) {
        this(null, loader);
    }

    /**
     * Default constructor without caching and without an ImageLoader (or the ImageLoader may
     * be set later).
     */
    public ImageProviderPipeline() {
        this(null, null);
    }

    /**
     * Executes the image converter pipeline. First, the image indicated by the ImageInfo instance
     * is loaded through an ImageLoader and then optionally converted by a series of
     * ImageConverters. At the end of the pipeline, the fully loaded and converted image is
     * returned.
     * @param info the image info object indicating the image to load
     * @param hints a Map of image conversion hints
     * @param context the session context
     * @return the requested image
     * @throws ImageException if an error occurs while loader or converting the image
     * @throws IOException if an I/O error occurs
     */
    public Image execute(ImageInfo info, Map hints, ImageSessionContext context)
                throws ImageException, IOException {
        return execute(info, null, hints, context);
    }

    /**
     * Executes the image converter pipeline. First, the image indicated by the ImageInfo instance
     * is loaded through an ImageLoader and then optionally converted by a series of
     * ImageConverters. At the end of the pipeline, the fully loaded and converted image is
     * returned.
     * @param info the image info object indicating the image to load
     * @param originalImage the original image to start the pipeline off or null if an ImageLoader
     *          is used
     * @param hints a Map of image conversion hints
     * @param context the session context
     * @return the requested image
     * @throws ImageException if an error occurs while loader or converting the image
     * @throws IOException if an I/O error occurs
     */
    public Image execute(ImageInfo info, Image originalImage,
            Map hints, ImageSessionContext context) throws ImageException, IOException {
        if (hints == null) {
            hints = Collections.EMPTY_MAP;
        }
        long start = System.currentTimeMillis();
        Image img = null;

        //Remember the last image in the pipeline that is cacheable and cache that.
        Image lastCacheableImage = null;

        int converterCount = converters.size();
        int startingPoint = 0;
        if (cache != null) {
            for (int i = converterCount - 1; i >= 0; i--) {
                ImageConverter converter = getConverter(i);
                ImageFlavor flavor = converter.getTargetFlavor();
                img = cache.getImage(info, flavor);
                if (img != null) {
                    startingPoint = i + 1;
                    break;
                }
            }

            if (img == null && loader != null) {
                //try target flavor of loader from cache
                ImageFlavor flavor = loader.getTargetFlavor();
                img = cache.getImage(info, flavor);
            }
        }
        if (img == null && originalImage != null) {
            img = originalImage;
        }

        boolean entirelyInCache = true;
        long duration;
        if (img == null && loader != null) {
            //Load image
            img = loader.loadImage(info, hints, context);
            if (log.isTraceEnabled()) {
                duration = System.currentTimeMillis() - start;
                log.trace("Image loading using " + loader + " took " + duration + " ms.");
            }

            //Caching
            entirelyInCache = false;
            if (img.isCacheable()) {
                lastCacheableImage = img;
            }
        }
        if (img == null) {
            throw new ImageException(
                    "Pipeline fails. No ImageLoader and no original Image available.");
        }

        if (converterCount > 0) {
            for (int i = startingPoint; i < converterCount; i++) {
                ImageConverter converter = getConverter(i);
                start = System.currentTimeMillis();
                img = converter.convert(img, hints);
                if (log.isTraceEnabled()) {
                    duration = System.currentTimeMillis() - start;
                    log.trace("Image conversion using " + converter + " took " + duration + " ms.");
                }

                //Caching
                entirelyInCache = false;
                if (img.isCacheable()) {
                    lastCacheableImage = img;
                }
            }
        }

        //Note: Currently we just cache the end result of the pipeline, not all intermediate
        //results as it is expected that the cache hit ration would be rather small.
        if (cache != null && !entirelyInCache) {
            if (lastCacheableImage == null) {
                //Try to make the Image cacheable
                lastCacheableImage = forceCaching(img);
            }
            if (lastCacheableImage != null) {
                if (log.isTraceEnabled()) {
                    log.trace("Caching image: " + lastCacheableImage);
                }
                cache.putImage(lastCacheableImage);
            }
        }
        return img;
    }

    private ImageConverter getConverter(int index) {
        return (ImageConverter)converters.get(index);
    }

    /**
     * In some cases the provided Image is not cacheable, nor is any of the intermediate Image
     * instances (for example, when loading a raw JPEG file). If the image is loaded over a
     * potentially slow network, it is preferrable to download the whole file and cache it
     * in memory or in a temporary file. It's not always possible to convert an Image into a
     * cacheable variant.
     * @param img the Image to investigate
     * @return the converted, cacheable Image or null if the Image cannot be converted
     * @throws IOException if an I/O error occurs
     */
    protected Image forceCaching(Image img) throws IOException {
        if (img instanceof ImageRawStream) {
            ImageRawStream raw = (ImageRawStream)img;
            if (log.isDebugEnabled()) {
                log.debug("Image is made cacheable: " + img.getInfo());
            }

            //Read the whole stream and hold it in memory so the image can be cached
            ByteArrayOutputStream baout = new ByteArrayOutputStream();
            InputStream in = raw.createInputStream();
            try {
                IOUtils.copy(in, baout);
            } finally {
                IOUtils.closeQuietly(in);
            }
            final byte[] data = baout.toByteArray();
            raw.setInputStreamFactory(new ImageRawStream.ByteArrayStreamFactory(data));
            return raw;
        }
        return null;
    }

    /**
     * Sets the ImageLoader that is used at the beginning of the pipeline if the image is not
     * loaded, yet.
     * @param imageLoader the image loader implementation
     */
    public void setImageLoader(ImageLoader imageLoader) {
        this.loader = imageLoader;
    }

    /**
     * Adds an additional ImageConverter to the end of the pipeline.
     * @param converter the ImageConverter instance
     */
    public void addConverter(ImageConverter converter) {
        //TODO check for compatibility
        this.converters.add(converter);
    }

    /** {@inheritDoc} */
    public String toString() {
        StringBuffer sb = new StringBuffer();
        sb.append("Loader: ").append(loader);
        if (converters.size() > 0) {
            sb.append(" Converters: ");
            sb.append(converters);
        }
        return sb.toString();
    }

    /**
     * Returns the overall conversion penalty for the pipeline. This can be used to choose among
     * different possible pipelines.
     * @return the overall penalty (a non-negative integer)
     */
    public int getConversionPenalty() {
        return getConversionPenalty(null).getValue();
    }

    /**
     * Returns the overall conversion penalty for the pipeline. This can be used to choose among
     * different possible pipelines.
     * @param registry the image implementation registry
     * @return the overall penalty (a non-negative integer)
     */
    public Penalty getConversionPenalty(ImageImplRegistry registry) {
        Penalty penalty = Penalty.ZERO_PENALTY;
        if (loader != null) {
            penalty = penalty.add(loader.getUsagePenalty());
            if (registry != null) {
                penalty = penalty.add(
                        registry.getAdditionalPenalty(loader.getClass().getName()));
            }
        }
        for (Object converter1 : converters) {
            ImageConverter converter = (ImageConverter) converter1;
            penalty = penalty.add(converter.getConversionPenalty());
            if (registry != null) {
                penalty = penalty.add(
                        registry.getAdditionalPenalty(converter.getClass().getName()));
            }
        }
        return penalty;
    }

    /**
     * Returns the target flavor generated by this pipeline.
     * @return the target flavor
     */
    public ImageFlavor getTargetFlavor() {
        if (converters.size() > 0) {
            return getConverter(converters.size() - 1).getTargetFlavor();
        } else if (this.loader != null) {
            return this.loader.getTargetFlavor();
        } else {
            return null;
        }
    }

}
