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This package supports the parsing of AIS messages in Java. AIS, the Automatic Identification System, is a system aiming at improving maritime safety by exchanging messages between ships, other vehicles in particular aircraft involved in search-and-rescue (SAR), and (fixed) base stations. To be precise, this package support the ITU-R M.1371-4 AIS standard. See our extensive javadoc and in particular the class AISParser for more information on how to use this package. The parser was used in the Poseidon project, and is improved in the Metis project to better handle uncertain information. Both projects were led by the Embedded Systems Institute. In both projects Thales Nederlands was the carrying industrial partner, and multiple Dutch universities participated.

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/* ESI AIS Parser
 * 
 * Copyright 2011/2012 by Pierre van de Laar & Pierre America (Embedded Systems Institute)
 * Copyright 2008 by Brian C. Lane 
 * All Rights Reserved
 * 
 */
package nl.esi.metis.aisparser;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.text.NumberFormat;
import java.util.Arrays;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import nl.esi.metis.aisparser.provenance.FileSource;

/** This class supports parsing of AIS messages from File.
 * 
 * @author Pierre America
 * @author Pierre van de Laar
 */
public class ReadPath {
	/** A pattern that matches a line in a file with an optional time stamp and a raw AIS message, used by the {@link #readFile readFile} method.
	 * The predefined pattern will fit most reasonable file formats. 
	 * If it does not work for you, you can always change it. */
	static public Pattern linePattern = Pattern.compile(".*?(\\d+(?:\\.\\d*)?)?\\D*(!(?:[A-Z]{2})VD[MO].*)");
	
	/** Reads a file with AIS messages and handles all individual messages in the file.
	 * @param file the file to be processed
	 */
	static private void readFile(File file, HandleSensorData lineHandler) {
		try {
			FileReader input = new FileReader(file);
			BufferedReader bufRead = new BufferedReader(input);
			double lastTime = 0;
			int lineCount = 0;

			String line; // String that holds current file line
			do {
				line = bufRead.readLine();
				if (line != null) {
					lineCount++;
					Matcher m = linePattern.matcher(line);
					if (m.matches())
					{
						assert (m.groupCount() == 2);
						if (m.group(1) != null){
							double newTime = Double.parseDouble(m.group(1));
							if (newTime < lastTime)
							{
								NumberFormat nf = NumberFormat.getInstance ();
								nf.setMaximumFractionDigits(3);
								String differenceString = nf.format((lastTime - newTime));
								String lastTimeString = nf.format(lastTime);
								String newTimeString = nf.format(newTime);
								
								
								System.err.println("Time goes backwards on line " + lineCount + " of file "+ file.getName()+": " + differenceString + " seconds backwards from "+ lastTimeString + " to "+ newTimeString);
							}
							lastTime = newTime;
						}
						FileSource fs = new FileSource(file, lineCount, line, lastTime);
						lineHandler.handleSensorData(fs, m.group(2));
					}
					else
					{
						if (line.length() > 200)
							line = line.substring(0, 200);
						System.err.println("Could not find VDM message on line number " + lineCount + " of file "+ file.getName() + ": " + line);
					}
				}
			} while (line != null);
			bufRead.close();
		} catch (IOException e) {
			e.printStackTrace();
		}
	}	
	
	public void readPath(String aisPath, HandleSensorData lineHandler) {
		readPath(aisPath, lineHandler, -1);
	}
	
	public void readPath(String aisPath, HandleSensorData lineHandler, long nrFiles) {
		File aisFile = new File(aisPath);
		if (aisFile.isFile()) {
			readFile(aisFile, lineHandler);
			lineHandler.finished();
		} else 
		if (aisFile.isDirectory()){
			readDirectory(aisFile, lineHandler, nrFiles);
			lineHandler.finished();
		} else {
			System.err.println("Illegal path '" + aisPath + "'" );
		}
	}
	
	/** Read all files in a directory (recursively)
	 * It is assumed that files end arbitrarily (e.g. per minute or per hour) such that AIS messages might be spread over multiple files.
	 * @param aisFile directory to read
	 * @param lineHandler handler of correct lines
	 * @param nrFiles maximum number of files to read (-1 indicates read all files)
	 */
	private void readDirectory(File aisFile, HandleSensorData lineHandler, long nrFiles) {
		File files[] = aisFile.listFiles();
		Arrays.sort(files);

		for (int i = 0; i < files.length && (nrFiles == -1 || nrofFilesRead < nrFiles); i++) {
			if (files[i].isFile()) {
				nrofFilesRead++;
				readFile(files[i], lineHandler);
			} else {
				readDirectory(files[i], lineHandler, nrFiles);
			}	
		}
	}
	
	private long nrofFilesRead =0;
}