com.github.bloodshura.sparkium.brainfxck.action.impl.DefaultAction Maven / Gradle / Ivy

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A highly extensible, simple interpreter for the Brainfuck language.
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package com.github.bloodshura.sparkium.brainfxck.action.impl;

import com.github.bloodshura.ignitium.charset.sequence.CharSet;
import com.github.bloodshura.ignitium.collection.map.XMap;
import com.github.bloodshura.ignitium.collection.store.impl.XStack;
import com.github.bloodshura.sparkium.brainfxck.BrainfuckContext;
import com.github.bloodshura.sparkium.brainfxck.BrainfuckInterpreter;
import com.github.bloodshura.sparkium.brainfxck.BrainfuckMemory;
import com.github.bloodshura.sparkium.brainfxck.action.Action;

import javax.annotation.Nonnull;
import java.io.IOException;

/**
 * The default Brainfuck action.
 *  It is responsible for handling the following Brainfuck input characters:
 * 

 * >, which increments the memory pointer
 * <, which decrements the memory pointer
 * +, which increments the value on the current memory pointer
 * -, which decrements the value on the current memory pointer
 * [, which starts a loop
 * ], which ends a loop if the value on the current memory pointer is zero, or returns to its beginning if otherwise
 * ,, which reads a character from {@link BrainfuckInterpreter#getScanner()} and stores it on the current memory pointer
 * ., which prints the value on the current memory pointer using {@link BrainfuckInterpreter#getLogger()}
 * 
 */
public class DefaultAction implements Action {
	/**
	 * A {@link CharSet} instance containing all the characters which are manipulated by this action.
	 *  See the documentation of this class for a detailed explanation of each character.
	 */
	public static final CharSet CHAR_SET = new CharSet('>', '<', '+', '-', '[', ']', ',', '.');

	/**
	 * The flag name used for loop skipping.
	 *
	 * @see BrainfuckContext#getFlags()
	 */
	public static final String FLAG_SKIP = "skipping";

	@Override
	public boolean act(char ch, @Nonnull BrainfuckContext context) throws IOException {
		BrainfuckInterpreter interpreter = context.getInterpreter();
		XStack loopStack = context.getLoopStack();
		BrainfuckMemory memory = interpreter.getMemory();
		XMap flags = context.getFlags();
		int skipLevel = (int) flags.get(FLAG_SKIP, 0);

		if (skipLevel > 0 && ch != ']') {
			return false;
		}

		if (ch == '>') {
			memory.increasePointer();
		} else if (ch == '<') {
			memory.decreasePointer();
		} else if (ch == '+') {
			memory.increaseValue();
		} else if (ch == '-') {
			memory.decreaseValue();
		} else if (ch == '[') {
			if (memory.getValue() == 0) {
				flags.set(FLAG_SKIP, skipLevel + 1);
			} else {
				loopStack.push(context.getCurrentIndex());
			}
		} else if (ch == ']') {
			if (skipLevel > 0) {
				flags.set(FLAG_SKIP, skipLevel - 1);
			} else if (!loopStack.isEmpty()) {
				int loopStart = loopStack.pop();

				if (memory.getValue() != 0) {
					loopStack.push(loopStart);
					context.setCurrentIndex(loopStart + 1);
				}
			}
		} else if (ch == ',') {
			memory.setValue(interpreter.readChar());
		} else if (ch == '.') {
			interpreter.getLogger().print((char) memory.getValue());
		} else {
			return false;
		}

		return true;
	}
}