/*
 *    GeoTools - The Open Source Java GIS Toolkit
 *    http://geotools.org
 *
 *    (C) 2008, Open Source Geospatial Foundation (OSGeo)
 *
 *    This library is free software; you can redistribute it and/or
 *    modify it under the terms of the GNU Lesser General Public
 *    License as published by the Free Software Foundation;
 *    version 2.1 of the License.
 *
 *    This library 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
 *    Lesser General Public License for more details.
 */
package org.geotools.data.shapefile;

import java.io.File;
import java.io.IOException;
import java.net.URL;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.FileChannel.MapMode;
import java.util.ArrayList;
import java.util.List;
import java.util.logging.Level;
import java.util.logging.Logger;

import org.geotools.data.DataUtilities;
import org.geotools.resources.NIOUtilities;
import org.geotools.util.SoftValueHashMap;
import org.geotools.util.SoftValueHashMap.ValueCleaner;
import org.geotools.util.logging.Logging;

/**
 * A cache for memory mapped buffers, used to avoid generating over and over
 * read only memory mapped buffers. Mapping a file is a synchronized operation,
 * plus by generating light copies the same buffer can be shared by various threads
 * @author Andrea Aime - OpenGeo
 *
 */
class MemoryMapCache {
	
	static final Logger LOGGER = Logging.getLogger(MemoryMapCache.class);

    SoftValueHashMap<MappingKey, MappedByteBuffer> buffers = new SoftValueHashMap<MappingKey, MappedByteBuffer>(0, new BufferCleaner());
    
	MappedByteBuffer map(FileChannel wrapped, URL url, MapMode mode, long position, long size) throws IOException {
		if(mode != MapMode.READ_ONLY) {
			return wrapped.map(mode, position, size);
		}
		
		File file = DataUtilities.urlToFile(url).getCanonicalFile();
		MappingKey mk = new MappingKey(file, position, size);
		MappedByteBuffer buffer = buffers.get(mk);
		if(buffer == null) {
			synchronized (this) {
				buffer = buffers.get(mk);
				if(buffer == null) {
					buffer = wrapped.map(mode, position, size);
					buffers.put(mk, buffer);
					if(LOGGER.isLoggable(Level.FINE)) {
						LOGGER.log(Level.FINE, "Mapping and caching " + file.getAbsolutePath());
					}
				}
			}
		} else {
			if(LOGGER.isLoggable(Level.FINE)) {
				LOGGER.log(Level.FINE, "Using cached map for " + file.getAbsolutePath());
			}
		}
		
		return (MappedByteBuffer) buffer.duplicate();
	}
	
	/**
	 * Cleans up all memory mapped regions for a specified file. It is necessary to call this
	 * method before any attempt to open a file for writing on Windows
	 * @param file
	 */
	void cleanFileCache(URL url) {
	    try {
    	    final File rawFile = DataUtilities.urlToFile(url);
    	    if(rawFile == null) {
    	        // not a local file
    	        return;
    	    }
            File file = rawFile.getCanonicalFile();
    	    List<MappingKey> keys = new ArrayList<MappingKey>(buffers.keySet());
    	    for (MappingKey key : keys) {
                if(key.file.equals(file)) {
                    MappedByteBuffer buffer = buffers.remove(key);
                    NIOUtilities.clean(buffer, true);
                    if(LOGGER.isLoggable(Level.FINE)) {
        				LOGGER.log(Level.FINE, "Removed mapping for " + file.getAbsolutePath());
                    }
                }
            }
	    } catch(Throwable t) {
	        LOGGER.log(Level.WARNING, "An error occurred while trying to clean the memory map cache", t);
	    }
	}
	
	void clean() {
		List<MappingKey> keys = new ArrayList<MappingKey>(buffers.keySet());
	    for (MappingKey key : keys) {
            MappedByteBuffer buffer = buffers.remove(key);
            NIOUtilities.clean(buffer, true);
            if(LOGGER.isLoggable(Level.FINE)) {
				LOGGER.log(Level.FINE, "Removed mapping for " + key.file.getAbsolutePath());
            }
        }
	}
	
	/**
	 * Tracks a memory mapped region of a certain file
	 */
	static class MappingKey {
		File file;
		long position;
		long size;
		
		public MappingKey(File file, long position, long size) {
			super();
			this.file = file;
			this.position = position;
			this.size = size;
		}

        @Override
        public int hashCode() {
            final int prime = 31;
            int result = 1;
            result = prime * result + ((file == null) ? 0 : file.hashCode());
            result = prime * result + (int) (position ^ (position >>> 32));
            result = prime * result + (int) (size ^ (size >>> 32));
            return result;
        }

        @Override
        public boolean equals(Object obj) {
            if (this == obj)
                return true;
            if (obj == null)
                return false;
            if (getClass() != obj.getClass())
                return false;
            MappingKey other = (MappingKey) obj;
            if (file == null) {
                if (other.file != null)
                    return false;
            } else if (!file.equals(other.file))
                return false;
            if (position != other.position)
                return false;
            if (size != other.size)
                return false;
            return true;
        }
	}
	
	/**
	 * Cleans up the buffers before the soft reference gets deallocated
	 * @author Andrea Aime
 *
 * @source $URL: http://svn.osgeo.org/geotools/trunk/modules/plugin/shapefile/src/main/java/org/geotools/data/shapefile/MemoryMapCache.java $
	 */
	public class BufferCleaner implements ValueCleaner {

        public void clean(Object object) {
            MappedByteBuffer buffer = (MappedByteBuffer) object;
            NIOUtilities.clean(buffer, true);
        }

    }


}