package com.metaweb.lessen.tokenizers;

import java.io.IOException;
import java.io.Reader;


public class ReaderTokenizer extends TokenizerBase {
    final static protected int s_bufferSize = 32;
    
    final protected Reader          _reader;
    final protected StringBuffer    _sb = new StringBuffer(s_bufferSize * 2);
    final protected char[]          _chars = new char[s_bufferSize];
    
    protected int                   _sbStartIndex = 0;
    protected int                   _next = 0;
    protected boolean               _eof = false;

    public ReaderTokenizer(Reader reader) {
        _reader = reader;
        next();
    }
    
    @Override
    protected boolean hasMoreChar() {
        return hasMoreChar(0);
    }

    @Override
    protected void advance() {
        advance(1, false);
    }

    @Override
    protected void advance(int by, boolean flush) {
        _next += by;
        if (flush) {
            flush(_next);
        }
    }

    @Override
    protected void flush(int upToIndex) {
        int chop = upToIndex - _sbStartIndex;
        if (chop > 0.75 * s_bufferSize) {
            _sb.delete(0, chop);
            _sbStartIndex += chop;
        }
    }

    @Override
    protected char getCharRelative(int offset) {
        tryLoadAhead(offset + 1);
        
        return _sb.charAt(_next - _sbStartIndex + offset);
    }

    @Override
    protected char getCurrentChar() {
        return getCharRelative(0);
    }

    @Override
    protected int getCurrentOffset() {
        return _next;
    }

    @Override
    protected String getText(int from, int to) {
        return _sb.substring(from - _sbStartIndex, to - _sbStartIndex);
    }

    @Override
    protected boolean hasMoreChar(int offset) {
        tryLoadAhead(offset + 1);
        
        return _next - _sbStartIndex + offset < _sb.length();
    }
    
    protected void tryLoadAhead(int distance) {
        if (_next - _sbStartIndex + distance > _sb.length() && !_eof) {
            try {
                int c = _reader.read(_chars);
                if (c < 0) {
                    _eof = true;
                    _reader.close();
                } else {
                    _sb.append(_chars, 0, c);
                }
            } catch (IOException e) {
                _eof = true;
            }
        }
    }
}