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/**
 * eobjects.org MetaModel
 * Copyright (C) 2010 eobjects.org
 *
 * This copyrighted material is made available to anyone wishing to use, modify,
 * copy, or redistribute it subject to the terms and conditions of the GNU
 * Lesser General Public License, as published by the Free Software Foundation.
 *
 * 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 Lesser General Public License
 * for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this distribution; if not, write to:
 * Free Software Foundation, Inc.
 * 51 Franklin Street, Fifth Floor
 * Boston, MA  02110-1301  USA
 */
package org.eobjects.metamodel.csv;

import java.io.File;
import java.io.IOException;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.RandomAccessFile;
import java.io.Writer;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.charset.Charset;

import org.eobjects.metamodel.AbstractUpdateCallback;
import org.eobjects.metamodel.MetaModelException;
import org.eobjects.metamodel.UpdateCallback;
import org.eobjects.metamodel.create.TableCreationBuilder;
import org.eobjects.metamodel.delete.RowDeletionBuilder;
import org.eobjects.metamodel.drop.TableDropBuilder;
import org.eobjects.metamodel.insert.RowInsertionBuilder;
import org.eobjects.metamodel.schema.Schema;
import org.eobjects.metamodel.schema.Table;
import org.eobjects.metamodel.update.RowUpdationBuilder;
import org.eobjects.metamodel.util.Action;
import org.eobjects.metamodel.util.EqualsBuilder;
import org.eobjects.metamodel.util.FileHelper;
import org.eobjects.metamodel.util.FileResource;
import org.eobjects.metamodel.util.Resource;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

final class CsvUpdateCallback extends AbstractUpdateCallback implements UpdateCallback {

    private static final Logger logger = LoggerFactory.getLogger(CsvUpdateCallback.class);

    private final CsvConfiguration _configuration;
    private final Resource _resource;
    private Writer _writer;

    public CsvUpdateCallback(CsvDataContext dataContext) {
        super(dataContext);
        _resource = dataContext.getResource();
        _configuration = dataContext.getConfiguration();
    }

    @Override
    public TableCreationBuilder createTable(Schema schema, String name) throws IllegalArgumentException, IllegalStateException {
        return new CsvCreateTableBuilder(this, schema, name);
    }

    @Override
    public RowInsertionBuilder insertInto(Table table) throws IllegalArgumentException, IllegalStateException {
        validateTable(table);
        return new CsvInsertBuilder(this, table);
    }

    public CsvConfiguration getConfiguration() {
        return _configuration;
    }

    public Resource getResource() {
        return _resource;
    }

    private void validateTable(Table table) {
        if (!(table instanceof CsvTable)) {
            throw new IllegalArgumentException("Not a valid CSV table: " + table);
        }
    }

    protected synchronized void writeRow(final String[] stringValues, final boolean append) {
        final CsvWriter _csvWriter = new CsvWriter(_configuration);
        final String line = _csvWriter.buildLine(stringValues);
        if (_resource instanceof FileResource) {
            // optimized handling for file-based resources
            final File file = ((FileResource) _resource).getFile();
            final Writer writer = getFileWriter(file, append);
            try {
                writer.write(line);
            } catch (IOException e) {
                throw new MetaModelException("Failed to write line to file: " + line, e);
            }
        } else {
            // generic handling for any kind of resource
            final Action action = new Action() {
                @Override
                public void run(OutputStream out) throws Exception {
                    final String encoding = _configuration.getEncoding();
                    final OutputStreamWriter writer = new OutputStreamWriter(out, encoding);
                    writer.write(line);
                    writer.flush();
                }
            };
            if (append) {
                _resource.append(action);
            } else {
                _resource.write(action);
            }
        }
    }

    private Writer getFileWriter(File file, boolean append) {
        if (_writer == null || !append) {
            final boolean needsLineBreak = needsLineBreak(file, _configuration);

            final Writer writer = FileHelper.getWriter(file, _configuration.getEncoding(), append);
            if (needsLineBreak) {
                try {
                    writer.write('\n');
                } catch (IOException e) {
                    logger.debug("Failed to insert newline", e);
                }
            }
            _writer = writer;
        }
        return _writer;
    }

    protected static boolean needsLineBreak(File file, CsvConfiguration configuration) {
        if (!file.exists() || file.length() == 0) {
            return false;
        }

        try {
            // find the bytes a newline would match under the encoding
            final byte[] bytesInLineBreak;
            {
                ByteBuffer encodedLineBreak = Charset.forName(configuration.getEncoding()).encode("\n");
                bytesInLineBreak = new byte[encodedLineBreak.capacity()];
                encodedLineBreak.get(bytesInLineBreak);
            }

            // find the last bytes of the file
            final byte[] bytesFromFile = new byte[bytesInLineBreak.length];
            {
                final RandomAccessFile randomAccessFile = new RandomAccessFile(file, "r");
                try {
                    FileChannel channel = randomAccessFile.getChannel();
                    try {
                        long length = randomAccessFile.length();

                        channel = channel.position(length - bytesInLineBreak.length);
                        channel.read(ByteBuffer.wrap(bytesFromFile));
                    } finally {
                        channel.close();
                    }
                } finally {
                    randomAccessFile.close();
                }
            }

            // if the two byte arrays match, then the newline is not needed.
            if (EqualsBuilder.equals(bytesInLineBreak, bytesFromFile)) {
                return false;
            }
            return true;
        } catch (Exception e) {
            logger.error("Error occurred while checking if file needs linebreak, omitting check", e);
        }
        return false;
    }

    /**
     * Closes all open handles
     */
    protected void close() {
        if (_writer != null) {
            try {
                _writer.flush();
            } catch (IOException e) {
                logger.warn("Failed to flush CSV writer", e);
            }
            try {
                _writer.close();
            } catch (IOException e) {
                logger.error("Failed to close CSV writer", e);
            } finally {
                _writer = null;
            }
        }
    }

    @Override
    public RowUpdationBuilder update(Table table) throws IllegalArgumentException, IllegalStateException {
        close();
        return super.update(table);
    }

    @Override
    public boolean isDropTableSupported() {
        return true;
    }

    @Override
    public TableDropBuilder dropTable(Table table) {
        validateTable(table);
        return new CsvTableDropBuilder(this, table);
    }

    /**
     * Callback method used by {@link CsvTableDropBuilder} when execute is
     * called
     */
    protected void dropTable() {
        close();
        if (_resource instanceof FileResource) {
            final File file = ((FileResource) _resource).getFile();
            final boolean success = file.delete();
            if (!success) {
                throw new MetaModelException("Could not delete (drop) file: " + file);
            }
        } else {
            _resource.write(new Action() {
                @Override
                public void run(OutputStream arg) throws Exception {
                    // do nothing, just write an empty file
                }
            });
        }
    }

    @Override
    public boolean isDeleteSupported() {
        return true;
    }

    @Override
    public RowDeletionBuilder deleteFrom(Table table) {
        validateTable(table);
        return new CsvDeleteBuilder(this, table);
    }
}