/src/org/faabtech/brainfuck/impl/TrollScriptEngine.java

package org.faabtech.brainfuck.impl;

import java.io.InputStream;
import java.io.OutputStream;
import java.io.PrintStream;
import java.util.ArrayList;
import java.util.List;

import org.faabtech.brainfuck.BrainfuckEngine;

/**
 * The {@link TrollScriptEngine} is an implementation for the
 * <code>brainfuck<code> dialect
 * 	<code>TrollScript</code>.
 * 
 * @author Fabian M.
 */
public class TrollScriptEngine extends BrainfuckEngine {

	/**
	 * The default length of a token.
	 */
	protected int defaultTokenLength = 3;
	/**
	 * The {@link Token} class contains tokens in <code>TrollScript</code>.
	 * 
	 * @author Fabian M.
	 */
	protected static class Token {

		public final static String START = "tro";
		public final static String NEXT = "ooo";
		public final static String PREVIOUS = "ool";
		public final static String PLUS = "olo";
		public final static String MINUS = "oll";
		public final static String OUTPUT = "loo";
		public final static String INPUT = "lol";
		public final static String BRACKET_LEFT = "llo";
		public final static String BRACKET_RIGHT = "lll";
		public final static String END = "ll.";
	}

	/**
	 * Constructs a new {@link TrollScriptEngine} instance.
	 * 
	 * @param cells
	 *            The amount of memory cells.
	 */
	public TrollScriptEngine(int cells) {
		this(cells, new PrintStream(System.out), System.in);
	}

	/**
	 * Constructs a new {@link TrollScriptEngine} instance.
	 * 
	 * @param cells
	 *            The amount of memory cells.
	 * @param out
	 *            The outputstream of this program.
	 */
	public TrollScriptEngine(int cells, OutputStream out) {
		this(cells, out, System.in);
	}

	/**
	 * Constructs a new {@link TrollScriptEngine} instance.
	 * 
	 * @param cells
	 *            The amount of memory cells.
	 * @param out
	 *            The printstream of this program.
	 * @param in
	 *            The outputstream of this program.
	 */
	public TrollScriptEngine(int cells, OutputStream out, InputStream in) {
		super(cells, out, in);
	}

	/**
	 * Interprets the given string.
	 * 
	 * @param str
	 *            The string to interpret.
	 * @throws Exception
	 */
	@Override
	public void interpret(String str) throws Exception {
		// Is this program already started?
		boolean started = false;
		// List with tokens.defaultTokenLenght
		List<String> tokens = new ArrayList<String>();
		// It fine that all TrollScript tokens are 3 characters long :)
		// So we aren't going to loop through all characters.
		for (; charPointer < str.length(); ) {
			String token = "";
			if (charPointer + defaultTokenLength <= str.length())
				// The string we found.
				token = str.substring(charPointer, charPointer + defaultTokenLength);
			else
				token = str.substring(charPointer, charPointer
						+ (str.length() - charPointer));
			// Is it a token?
			if (isValidToken(token)) {
				if (token.equalsIgnoreCase(Token.START))
					started = true;
				else if (token.equalsIgnoreCase(Token.END))
					break;
				else if (started)
					tokens.add(token);
				charPointer += defaultTokenLength;
			} else if (charPointer + defaultTokenLength > str.length()) {
				charPointer += (str.length() - charPointer);
			} else {
				charPointer++;
			}
		} 
		
		// Loop through all tokens.
		for (int tokenPointer = 0; tokenPointer < tokens.size(); ) {
			String token = tokens.get(tokenPointer);
		
			if (token.equalsIgnoreCase(Token.NEXT)) {
				// increment the data pointer (to point to the next cell
				// to the
				// right).
				dataPointer = (dataPointer == data.length - 1 ? 0 : dataPointer + 1);
			} 
			if (token.equalsIgnoreCase(Token.PREVIOUS)) {
				// decrement the data pointer (to point to the next cell
				// to the
				// left).
				dataPointer = (dataPointer == 0 ? data.length - 1 : dataPointer - 1);
			} 
			if (token.equalsIgnoreCase(Token.PLUS)) {
				// increment (increase by one) the byte at the data
				// pointer.
				data[dataPointer]++;
			} 
			if (token.equalsIgnoreCase(Token.MINUS)) {
				// decrement (decrease by one) the byte at the data
				// pointer.
				data[dataPointer]--;
			}
			if (token.equalsIgnoreCase(Token.OUTPUT)) {
				// Output the byte at the current index in a character.
				outWriter.write((char) data[dataPointer]);
				// Flush the outputstream.
				outWriter.flush();
			} 
			if (token.equalsIgnoreCase(Token.INPUT)) {
				// accept one byte of input, storing its value in the
				// byte at the data pointer.
				data[dataPointer] = (byte) consoleReader.read();
			} 
			if (token.equalsIgnoreCase(Token.BRACKET_LEFT)) {
				if (data[dataPointer] == 0) {
					int level = 1;
					while (level > 0) {	
						tokenPointer++;
						
						if (tokens.get(tokenPointer).equalsIgnoreCase(Token.BRACKET_LEFT)) 
							level++;
						else if (tokens.get(tokenPointer).equalsIgnoreCase(Token.BRACKET_RIGHT))
							level--;
					}
				}
			}
			if (token.equalsIgnoreCase(Token.BRACKET_RIGHT)) {
				if (data[dataPointer] != 0) {
					int level = 1;
					while (level > 0) {
						tokenPointer--;
						
						if (tokens.get(tokenPointer).equalsIgnoreCase(Token.BRACKET_LEFT)) 
							level--;
						else if (tokens.get(tokenPointer).equalsIgnoreCase(Token.BRACKET_RIGHT))
							level++;
					}
				}
			}
			
			tokenPointer++;
		}
		// Clear all data.
		initate(data.length);
	}

	/**
	 * Is the given token a valid <code>TrollScript</code> token.
	 * 
	 * @param token
	 *            The token to check.
	 * @return <code>true</code> if the given token is a valid
	 *         <code>TrollScript</code> token, <code>false</code> otherwise.
	 */
	protected boolean isValidToken(String token) {
		if (token.equalsIgnoreCase(Token.START) || token.equalsIgnoreCase(Token.NEXT)
				|| token.equalsIgnoreCase(Token.PREVIOUS) || token.equalsIgnoreCase(Token.PLUS)
				|| token.equalsIgnoreCase(Token.MINUS) || token.equalsIgnoreCase(Token.OUTPUT)
				|| token.equalsIgnoreCase(Token.INPUT)
				|| token.equalsIgnoreCase(Token.BRACKET_LEFT)
				|| token.equalsIgnoreCase(Token.BRACKET_RIGHT)
				|| token.equalsIgnoreCase(Token.END)) {
			return true;
		}
		return false;
	}

}