/* ======================================================================
   Parts Copyright 2006 University of Leeds, Oxford University, University of the Highlands and Islands.

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.

====================================================================== */

package org.bodington.util;

import java.io.*;

public class CsvReader
	{
	BufferedReader reader;
	boolean start_of_line, end_of_line, end_of_file;
	
	public CsvReader( Reader reader )
		throws IOException
		{
		this.reader = new BufferedReader( reader );
		end_of_line = true;
		end_of_file = false;
		}
		
	public boolean nextLine()
		throws IOException
		{
		if ( !end_of_line )
			throw new IOException( "Can only call nextLine() at end of line." );
		end_of_line=false;
		start_of_line=true;
		return !end_of_file;
		}

	public String readField()
		throws IOException
		{
		if ( end_of_line )
			return null;
		if ( end_of_file )
			return null;
			
		
		StringBuffer field = new StringBuffer();
		boolean in_quote=false, is_quoted=false, in_whitespace=true;
		int c, last_c=-1;
		

		while ( (c=reader.read()) != -1 )
			{
			// just skip past control characters no matter where they are
			// placed
			if ( Character.isIdentifierIgnorable( (char)c ) )
				continue;
				
			if ( c=='\"' )
				{
				if ( !is_quoted )
					{
					// first quote found in the field
					
					// erase leading whitespace
					if ( in_whitespace )
						{
						in_whitespace=false;
						field.setLength( 0 );
						}
					is_quoted=true;
					in_quote=true;
					}
				else
					{
					// If this is an open quote immediately after a 
					// close quote then it is actually an escaped literal
					// quote character.
					if ( !in_quote && last_c == '\"' )
						field.append( "\"" );
					// either this is the first or second character in an escaped quote ""
					// or its the the end of the field
					// just change flag and deal with what comes next
					in_quote=!in_quote;
					}
				}
			else
				{
				// anything other than quote
				// action depends on whether we are in a quoted field
				
				if ( is_quoted && in_quote )
					{
					// anything appearing in the quotes is part of the
					// field including white space.
					// (end quote will complete it and end of file will
					// throw an exception.
					field.append( (char)c );
					}
				else
					{
					// at field delimiter?
					if ( c == ',' )
						{
						// discard comma and return field
						// even if there's nothing after the comma
						// it will count as a field so don't signal
						// end of line.
						return field.toString();
						}
						
					// at line delimiter?
					if ( c == '\n' )
						{
						end_of_line=true;
						// if the line had nothing but white space
						// (we are still at start) there is no field
						// to return.
						if ( start_of_line )
							return null;
							
						return field.toString();
						}
						
					// not a delimiter...
					
					// between or after quoted section?
					if ( is_quoted )
						{
						// non-white space is invalid
						if ( !Character.isWhitespace( (char)c ) )
							throw new IOException( "Invalid file format. Misplaced quotes." );
						//white space discarded
						}
					else
						{
						// any characters inside field are added on
						field.append( (char)c );
						}
					}
				}
			
			// whatever turns up that isn't white space - we aren't
			// at the start of the line anymore.
			if ( !Character.isWhitespace( (char)c ) )
				start_of_line=false;
				
			last_c = c;
			}
			
		
		// reached end of file
		end_of_file = true;
		end_of_line = true;
		
		// if in incomplete field throw exception
		if ( in_quote )
			throw new IOException( "Unexpected end of file." );
		
		if ( start_of_line )
			return null;
			
		return field.toString();
		}
	}