SymbolFactory.java

package org.ggp.base.util.symbol.factory;

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;

import org.ggp.base.util.symbol.factory.exceptions.SymbolFormatException;
import org.ggp.base.util.symbol.grammar.Symbol;
import org.ggp.base.util.symbol.grammar.SymbolAtom;
import org.ggp.base.util.symbol.grammar.SymbolList;
import org.ggp.base.util.symbol.grammar.SymbolPool;


public final class SymbolFactory
{
    private SymbolFactory() {
    }

    public static Symbol create(String string) throws SymbolFormatException
    {
        try
        {
            String preprocessed = preprocess(string);
            List<String> tokens = lex(preprocessed);
            return convert(new LinkedList<String>(tokens));
        }
        catch (Exception e)
        {
            throw new SymbolFormatException(string);
        }
    }

    /* Private, implementation-specific methods below here */

    private static Symbol convert(LinkedList<String> tokens)
    {
        if (tokens.getFirst().equals("("))
        {
            return convertList(tokens);
        }
        else
        {
            return convertAtom(tokens);
        }
    }

    private static SymbolAtom convertAtom(LinkedList<String> tokens)
    {
        return SymbolPool.getAtom(tokens.removeFirst());
    }

    private static SymbolList convertList(LinkedList<String> tokens)
    {
        List<Symbol> contents = new ArrayList<Symbol>();

        tokens.removeFirst();
        while (!tokens.getFirst().equals(")"))
        {
            contents.add(convert(tokens));
        }
        tokens.removeFirst();

        return SymbolPool.getList(contents);
    }

    private static List<String> lex(String string)
    {
        List<String> tokens = new ArrayList<String>();
        for (String token : string.split(" "))
        {
            tokens.add(token);
        }

        return tokens;
    }

    private static String preprocess(String string)
    {
        string = string.replaceAll("\\(", " ( ");
        string = string.replaceAll("\\)", " ) ");

        string = string.replaceAll("\\s+", " ");
        string = string.trim();

        return string;
    }
}