/*
 *    GDBMWrapper.java
 *    Copyright (C) 2008 New Zealand Digital Library, http://www.nzdl.org
 *
 *    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 2 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, write to the Free Software
 *    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */
package org.greenstone.gsdl3.util;

import au.com.pharos.gdbm.GdbmFile;
import au.com.pharos.packing.*;
import au.com.pharos.gdbm.GdbmException;

import org.apache.log4j.Logger;

import java.io.UnsupportedEncodingException;
import java.io.File;

/**
 * java wrapper class for gdbm - uses Java-GDBM written by Martin Pool replaces
 * gdbmclass in the old version
 */

public class GDBMWrapper implements FlatDatabaseWrapper
{

	static Logger logger = Logger.getLogger(org.greenstone.gsdl3.util.GDBMWrapper.class.getName());

	/*
	 * GdbmFile modes: READER - read access, many readers may share the database
	 * WRITER - read/write access, exclusive access WRCREAT - read/write access,
	 * create db if doesn't exist NEWDB - read/write access, db should be
	 * replaced if exists
	 */

	protected GdbmFile db_ = null;

	/**
	 * open the database filename, with mode mode - uses the constants above, eg
	 * GdbmFile.WRITER
	 */
	public boolean openDatabase(String filename, int mode)
	{
		// need to convert mode to GdbmFile mode
		if (mode == READ)
		{
			mode = GdbmFile.READER;
		}
		else if (mode == WRITE)
		{
			mode = GdbmFile.WRITER;
		}
		else
		{
			logger.error("invalid mode, " + mode + ", opening db for reading only");
			mode = GdbmFile.READER;
		}
		try
		{
			if (db_ != null)
			{
				db_.close();
			}

			// The java version of the C++ code in common-src/src/lib/gdbmclass.cpp
			if (mode == GdbmFile.READER)
			{
				// Looking to read in the database
				// we now use gdb extension. Check for ldb/bdb in case of legacy collection
				// if not (first time) then generate using txt2db
				if (!new File(filename).exists())
				{
					logger.warn("Database file " + filename + " does not exist. Looking for ldb/bdb version");
					int extension = filename.lastIndexOf('.');
					String filename_head = filename.substring(0, extension);
					filename = filename_head + ".ldb";
					if (!new File(filename).exists())
					{
						filename = filename_head + ".bdb";

						if (!new File(filename).exists())
						{
							logger.warn("ldb/bdb version of database file " + filename + " does not exist. Looking for txtgz version of db file.");
							// put the filename back to gdb
							filename = filename_head + ".gdb";
							// need to generate architecture native GDBM file using txt2db

							// replace sought after gdbm filename ext with ".txt.gz"

							String txtgzFilename = filename_head + ".txt.gz";
							if (new File(txtgzFilename).exists())
							{
								// Test to make sure Perl is on the path
								// On Linux, the output of the test goes to STDOUT so redirect it to STDERR
								String cmdTest = "perl -v 2>&1";
								//String cmdTest = "echo %PATH%";
								int returnValue = Processing.runProcess(cmdTest);
								if (returnValue != 0)
								{
									logger.error("Tried to find Perl. Return exit value of running " + cmdTest + ": " + returnValue + ", (expected this to be 0)");
									logger.error("Check that Perl is set in your PATH environment variable.");
									//log.error("At present, PATH=" + System.getenv("PATH"));
								}

								String cmd = "perl -S txtgz-to-gdbm.pl \"" + txtgzFilename + "\" \"" + filename + "\"";
								returnValue = Processing.runProcess(cmd);
								// For some reason, launching this command with gsdl_system() still returns 1
								// even when it returns 0 when run from the command-line. We can check whether
								// we succeeded by looking at whether the output database file was created.
								if (returnValue != 0)
								{
									logger.warn("Warning, non-zero return value on running command \"" + cmd + "\": " + returnValue);
									if (!new File(filename).exists())
									{
										logger.error("Tried to run command \"" + cmd + "\", but it failed");
									}
								}
							}
						}
					}

				}
			}

			db_ = new GdbmFile(filename, mode);
		}
		catch (GdbmException e)
		{ // the database wasn't opened or created
			logger.error("couldn't open database " + filename);
			return false;
		}
		db_.setKeyPacking(new StringPacking());
		db_.setValuePacking(new StringPacking());
		return true;
	}

	/** close the database associated with this wrapper */
	public void closeDatabase()
	{
		try
		{
			if (db_ != null)
			{
				db_.close();
				db_ = null;
				if (System.getProperty("os.name").startsWith("Windows"))
				{
					//Hack: force Windows to let go of the gdb file
					System.gc();
				}
			}
		}
		catch (GdbmException e)
		{
			// should never get here - close never actually throws an exception
			logger.error("error on close()");
		}
	}

	public String getValue(String key)
	{
		if (db_ == null)
		{
			return null;
		}
		String s_info;
		try
		{
			try
			{
				// The key is UTF8: do db lookup using the UTF8 version of key
				s_info = (String) db_.fetch(key.getBytes("UTF-8"));
			}
			catch (UnsupportedEncodingException e)
			{
				logger.warn("utf8 key for " + key + " unrecognised. Retrying with default encoding.");
				// retry db lookup using default encoding of key instead of UTF8
				s_info = (String) db_.fetch(key);
			}
		}
		catch (GdbmException e)
		{
			logger.error("couldn't get record");
			return null;
		}
		if (s_info == null)
		{
			// record not present
			logger.error("key " + key + " not present in db");
			return null;
		}
		return s_info;
	}

	/**
	 * sets the given key to the given value in the database
	 */
	public boolean setValue(String key, String value)
	{
		if (db_ == null || !db_.isWritable())
		{
			logger.error("GDBM database is either null or not writable");
			return false;
		}
		
		try
		{
			db_.store(key, value);
		}
		catch (GdbmException ex)
		{
			logger.error("Error storing " + key + " = " + value + " in GDBM database");
			logger.error("Error message is: " + ex.getMessage());
			return false;
		}
		return true;
	}

	/**
	 * deletes the entry for given key
	 */
	public boolean deleteKey(String key)
	{
		if (db_ == null)
		{
			logger.error("GDBM database is null");
			return false;
		}
		
		try
		{
			db_.delete(key);
		}
		catch (GdbmException ex)
		{
			logger.error("Error deleting key " + key + " from the database");
			logger.error("Error message is: " + ex.getMessage());
			return false;
		}
		
		return true;
	}

	/**
	 * returns a string of key-value entries that can be printed for debugging
	 * purposes.
	 */
	public String displayAllEntries()
	{
		StringBuffer output = new StringBuffer();
		try
		{
			java.util.Enumeration e = db_.keys();
			while (e.hasMoreElements())
			{
				Object key = e.nextElement();
				Object value = db_.fetch(key);

				output.append("key href: ");
				output.append((String) key);
				output.append("\tvalue ID: ");
				output.append((String) value);
				output.append("\n");
				//logger.warn("key: " + key + "\tvalue: " + value);

				String urlkey = java.net.URLEncoder.encode((String) key, "UTF8");
				output.append("URL encoded key: " + urlkey);
				//logger.warn("URL encoded key: " + urlkey);
			}
		}
		catch (UnsupportedEncodingException e)
		{
			logger.warn("Trouble converting key to UTF-8.");
		}
		catch (Exception e)
		{
			logger.warn("Exception encountered when trying to displayAllEntries():" + e);
		}
		return output.toString();
	}
}