// File: Fields0.java

import java.io.*;

/** Demonstrate the ability to scan a file, find a part of the file
 *  and extract and store unique fields from the file.  Also shows
 *  documentation in javadoc form.
 *
 *  @author David G. Green */

public class Fields0 {
	/** known fields */
	static String [] fields = new String[100];
	/** number of known fields */
	static int n_fields = 0;                    // number of fields
	/** buffered input stream to file */
	static BufferedReader in = null;

	// definitions of the markers
	static final String BEGIN_RECORD_TAG = "<!:BEGIN:!>";
	static final String END_RECORD_TAG = "<!:END:!>";
	
	/** main program */
	public static void main ( String[] args ) throws IOException
	{
		System.out.println("Fields");

		// Open File
		try
		{
			in = new BufferedReader ( new FileReader("test.txt") );
		}
		catch ( FileNotFoundException ex )
		{
			System.out.println("Could not open test.txt");
			// bail out
			return;
		}

		// process file finding a record, processing till no more records
		while( true )
		{
			// Find start of record
			
			if (! seekStartOfRecord() ) // none
				break;
			
			// Discover fields in this record
			updateFields();
		}

		// Print fields		
		printFields();
	}

	/** seek the start of a record in the input stream 
	 *
	 *  @returns  whether or not start of record is found
	 */
	public static boolean seekStartOfRecord() throws IOException
	{
		String line;
		while ( true )
		{
			// read line
			line = getLine();
		 
			if ( line == null )
				return false;    // hit EOF
			
			// return when we have read the beginning of the record
			if ( line.equals(BEGIN_RECORD_TAG) )
				return true;

			// else keep reading
		}
	}
	
	/** get a line from the input stream */
	public static String getLine() throws IOException
	{
		return in.readLine();
	}

	/** read the current record, extract the field, and update the list
	 *  of known fields
	 */
	public static void updateFields() throws IOException
	{
		String line;
		String a_field;

		while ( true )
		{
			// read a line, quit at end of record
			// bug: don't handle "early" EOF
			line = getLine();
			if ( line.equals(END_RECORD_TAG) )
				break;

			// extract field
		    a_field = line.substring(0,line.indexOf("="));

			// if field not there, then add it
			if ( findField( a_field ) == -1 )
			{
				fields[n_fields]=a_field;
				n_fields++;
			}
		}
	}

	/** print out the known fields */
	public static void printFields()
	{
		System.out.println("Discovered Fields");
		if ( n_fields == 0 )
			System.out.println( "(none)");
		else
		{
			for (int i=0; i < n_fields; i++ )
				System.out.println( fields[i] );
		}
	}

	
	/** try to find a field in the list of known fields
	 *
	 *  @param    fld - the field to try to find
	 *  @returns  index into list if found or -1 if not found
	 */
	public static int findField( String fld)
	{
		for ( int i = 0; i < n_fields; i++ )
		{
			if ( fields[i].equals( fld ) )
				return i;
		}
		// if not found, return -1
		return -1;
		
	}
}