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Miscellaneous basic Java tools.
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/*
 * Copyright (c) 2017, Numdata BV, The Netherlands.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *     * Redistributions of source code must retain the above copyright
 *       notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above copyright
 *       notice, this list of conditions and the following disclaimer in the
 *       documentation and/or other materials provided with the distribution.
 *     * Neither the name of Numdata nor the
 *       names of its contributors may be used to endorse or promote products
 *       derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL NUMDATA BV BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package com.numdata.oss;

import java.io.*;
import java.util.*;

import org.jetbrains.annotations.*;

/**
 * Reads character-separated values (CSV) from a stream.
 *
 * The current implementation is not strictly RFC 4180 compliant:
 *
 * 

 *
 * Leading and trailing whitespace is removed if not quoted.
 *
 * Only '\n' is recognized as a line ending.
 *
 * Line endings can not be quoted.
 *
 * 
 *
 * @author Gerrit Meinders
 * @author G.B.M. Rupert
 * @see RFC 4180: Common Format and
 * MIME Type for Comma-Separated Values (CSV) Files
 */
public class CSVReader
{
	/**
	 * Underlying stream.
	 */
	private final Reader _in;

	/**
	 * Value separator.
	 */
	private char _separator = ',';

	/**
	 * Skip lines that start with a '#'.
	 */
	private boolean _skipComments = false;

	/**
	 * Skip rows that have no non-empty columns.
	 */
	private boolean _skipEmptyRows = false;

	/**
	 * Look-ahead stored by {@link #readRow()}.
	 */
	private char _ch = (char)-1;

	/**
	 * Constructs a new instance.
	 *
	 * @param in Stream to read from.
	 */
	public CSVReader( final Reader in )
	{
		_in = in;
	}

	public char getSeparator()
	{
		return _separator;
	}

	public void setSeparator( final char separator )
	{
		_separator = separator;
	}

	public boolean isSkipComments()
	{
		return _skipComments;
	}

	public void setSkipComments( final boolean skipComments )
	{
		_skipComments = skipComments;
	}

	public boolean isSkipEmptyRows()
	{
		return _skipEmptyRows;
	}

	public void setSkipEmptyRows( final boolean skipEmptyRows )
	{
		_skipEmptyRows = skipEmptyRows;
	}

	/**
	 * Reads all rows from the underlying stream.
	 *
	 * @return Rows of CSV data.
	 *
	 * @throws IOException if an I/O error occurs.
	 */
	@NotNull
	public List> readAll()
	throws IOException
	{
		final List> result = new ArrayList>();
		for ( List row = readRow(); row != null; row = readRow() )
		{
			result.add( row );
		}
		return result;
	}

	/**
	 * Reads the next row of CSV data from the underlying stream.
	 *
	 * @return Row of CSV data; {@code null} at end of input.
	 *
	 * @throws IOException if an I/O error occurs.
	 */
	@Nullable
	public List readRow()
	throws IOException
	{
		final Reader in = _in;

		final char separator = _separator;
		final boolean skipComments = _skipComments;
		final boolean skipEmptyRows = _skipEmptyRows;

		List result = null;
		final List row = new ArrayList();
		final StringBuilder value = new StringBuilder();

		boolean quotedValue = false;
		boolean quotesStarted = false;
		boolean quotesEnded = false;
		boolean valueStarted = false;
		boolean rowStarted = false;

		int whitespace = 0;

		char ch = _ch;
		do
		{
			char next = (char)in.read();

			if ( ch != (char)-1 )
			{
				if ( ( ch == '#' ) && skipComments && !rowStarted )
				{
					while ( ( next != '\n' ) && ( next != (char)-1 ) )
					{
						ch = next;
						next = (char)in.read();
					}
				}
				else if ( ch == separator )
				{
					if ( quotesStarted )
					{
						value.append( ch );
						valueStarted = true;
					}
					else
					{
						if ( whitespace > 0 )
						{
							value.setLength( value.length() - whitespace );
							whitespace = 0;
						}

						row.add( value.toString() );

						value.setLength( 0 );
						quotedValue = false;
						quotesStarted = false;
						quotesEnded = false;
						valueStarted = false;
					}
					rowStarted = true;
				}
				else if ( ch == '"' )
				{
					if ( quotesStarted )
					{
						if ( next == '"' )
						{
							next = (char)in.read(); // Ignore next '"'.
							value.append( ch );
							valueStarted = true;
						}
						else
						{
							quotesEnded = true;
							quotesStarted = false;
						}
					}
					else
					{
						quotedValue = true;
						quotesStarted = true;
						quotesEnded = false;
						valueStarted = false;

						whitespace -= value.length();
						value.setLength( 0 ); // All characters before the quotes are ignored.
					}
					rowStarted = true;
				}
				else if ( Character.isWhitespace( ch ) )
				{
					if ( ch != '\n' )
					{
						if ( quotesStarted ) // Skip unquoted leading whitespace.
						{
							value.append( ch );
							valueStarted = true;
						}
						else if ( valueStarted ) // Include contained whitespace.
						{
							value.append( ch );
							whitespace++;
						}
					}
				}
				else
				{
					if ( quotedValue )
					{
						if ( !quotesEnded )
						{
							value.append( ch );
							valueStarted = true;
						}
					}
					else
					{
						value.append( ch );
						valueStarted = true;
						whitespace = 0;
					}
					rowStarted = true;
				}

				if ( ( ch == '\n' ) || ( next == (char)-1 ) )
				{
					if ( rowStarted )
					{
						if ( valueStarted )
						{
							if ( whitespace > 0 )
							{
								value.setLength( value.length() - whitespace );
								whitespace = 0;
							}

							row.add( value.toString() );
						}

						boolean addRow = true;
						if ( skipEmptyRows )
						{
							addRow = false;

							for ( final String column : row )
							{
								if ( !column.isEmpty() )
								{
									addRow = true;
									break;
								}
							}
						}

						if ( addRow )
						{
							_ch = next;
							result = row;
							break;
						}
					}

					row.clear();
					value.setLength( 0 );
					quotedValue = false;
					quotesStarted = false;
					quotesEnded = false;
					valueStarted = false;
					rowStarted = false;
				}
			}

			ch = next;
		}
		while ( ch != (char)-1 );

		return result;
	}
}