/*
 * Syncany, www.syncany.org
 * Copyright (C) 2011-2016 Philipp C. Heckel <philipp.heckel@gmail.com> 
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package org.syncany.chunk;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Map;
import java.util.logging.Level;
import java.util.logging.Logger;

import org.syncany.database.MultiChunkEntry.MultiChunkId;
import org.syncany.util.StringUtil;

/**
 * A multichunker combines a set of {@link Chunk}s into a single file. It can be implemented
 * by a simple container or archive format. The multichunker is used by the {@link Deduper}
 * to write multichunks, and by other parts of the application to read multichunks and
 * re-assemble files.
 * 
 * <p>The class supports two modes: 
 * 
 * <ul>
 * <li>When writing a {@link MultiChunker}, the {@link #createMultiChunk(MultiChunkId, OutputStream)}
 *     must be used. The method emits a new implementation-specific {@link MultiChunk} 
 *     to which new chunks can be added/written to.
 *      
 * <li>When reading a multichunk from a file or input stream, the {@link #createMultiChunk(InputStream)}
 *     or {@link #createMultiChunk(File)} must be used. The emitted multichunk object can be read from.
 * </ul>
 * 
 * <p><b>Important:</b> Implementations must make sure that when providing a readable multichunk,
 * the individual chunk objects must be randomly accessible. A sequential read (like with TAR, for
 * instance), is not sufficient for the quick processing required in the application.
 *
 * @author Philipp C. Heckel (philipp.heckel@gmail.com)
 */
// TODO [low] The multichunk API is really odd; Think of something more sensible
public abstract class MultiChunker {

        /**
         * Minimal multi chunk size in KB.
         */
        public static final String PROPERTY_SIZE = "size";

        private static Logger logger = Logger.getLogger(MultiChunker.class.getSimpleName());

        protected int minMultiChunkSize; // in KB

        /**
         * Creates new multichunker without setting the minimum size of a multichunk.
         */
        public MultiChunker() {
                // Nothing.
        }

        /**
         * Initializes the multichunker using a settings map. 
         * <br>
         * Required settings are: 
         * <ul>
         *  <li> key: {@link #PROPERTY_SIZE}, value: integer encoded as String 
         * </ul>
         */
        public void init(Map<String, String> settings) {
                String size = settings.get(PROPERTY_SIZE);
                
                if (size == null) {
                        logger.log(Level.SEVERE, String.format("Property %s must not be null.", PROPERTY_SIZE));
                        throw new IllegalArgumentException(String.format("Property %s must not be null.", PROPERTY_SIZE));
                }
                
                try {
                        this.minMultiChunkSize = Integer.parseInt(size);
                }
                catch (NumberFormatException nfe) {
                        logger.log(Level.SEVERE, String.format("Property %s could not be parsed as Integer.", PROPERTY_SIZE));
                        throw new IllegalArgumentException(String.format("Property %s could not be parsed as Integer.", PROPERTY_SIZE));
                }
        }

        /**
         * Creates a new multichunker, and sets the minimum size of a multichunk.
         * 
         * <p>Implementations should react on the minimum multichunk size by allowing
         * at least the given amount of KBs to be written to a multichunk, and declaring
         * a multichunk 'full' if this limit is reached.
         * 
         * @param minMultiChunkSize Minimum multichunk file size in kilo-bytes
         */
        public MultiChunker(int minMultiChunkSize) {
                this.minMultiChunkSize = minMultiChunkSize;
        }

        /**
         * Create a new multichunk in <b>write mode</b>.
         * 
         * <p>Using this method only allows writing to the returned multichunk. The resulting
         * data will be written to the underlying output stream given in the parameter. 
         *   
         * @param id Identifier of the newly created multichunk 
         * @param os Underlying output stream to write the new multichunk to
         * @return Returns a new multichunk object which can only be used for writing 
         * @throws IOException
         */
        public abstract MultiChunk createMultiChunk(MultiChunkId id, OutputStream os) throws IOException;

        /**
         * Open existing multichunk in <b>read mode</b> using an underlying input stream.
         * 
         * <p>Using this method only allows reading from the returned multichunk. The underlying
         * input stream is opened and can be used to retrieve chunk data.
         * 
         * @param is InputStream to initialize an existing multichunk for read-operations only
         * @return Returns an existing multichunk object that allows read operations only
         */
        public abstract MultiChunk createMultiChunk(InputStream is);

        /**
         * Open existing multichunk in <b>read mode</b> using an underlying file.
         * 
         * <p>Using this method only allows reading from the returned multichunk. The underlying
         * input stream is opened and can be used to retrieve chunk data.
         * 
         * @param file File to read into a multichunk for read-operations only
         * @return Returns an existing multichunk object that allows read operations only
         */
        public abstract MultiChunk createMultiChunk(File file) throws IOException;

        /**
         * Returns a comprehensive string representation of a multichunker
         */
        public abstract String toString();

        /**
         * Instantiates a multichunker by its name using the default constructor. 
         * <br>
         * After creating a new multichunker, it must be initialized using the 
         * {@link #init(Map) init()} method. The given type attribute is mapped to fully 
         * qualified class name (FQCN) of the form <code>org.syncany.chunk.XMultiChunker</code>,
         * where <code>X</code> is the camel-cased type attribute.
         * 
         * @param type Type/name of the multichunker (corresponds to its camel case class name)
         * @return a new multichunker
         */
        public static MultiChunker getInstance(String type) {
                String thisPackage = MultiChunker.class.getPackage().getName();
                String camelCaseName = StringUtil.toCamelCase(type);
                String fqClassName = thisPackage + "." + camelCaseName + MultiChunker.class.getSimpleName();

                // Try to load!
                try {
                        Class<?> clazz = Class.forName(fqClassName);
                        return (MultiChunker) clazz.newInstance();
                }
                catch (Exception ex) {
                        logger.log(Level.INFO, "Could not find multichunker FQCN " + fqClassName, ex);
                        return null;
                }
        }
}