package nebula.vm;

/***
 * Excerpted from "Language Implementation Patterns",
 * published by The Pragmatic Bookshelf.
 * Copyrights apply to this code. It may not be used to create training material, 
 * courses, books, articles, and the like. Contact us if you are in doubt.
 * We make no guarantees that this code is fit for any purpose. 
 * Visit http://www.pragmaticprogrammer.com/titles/tpdsl for more book information.
 ***/
import java.util.*;

public class LabelSymbol {
	String name;

	/** Address in code memory */
	int address;

	/** Is this ref'd before def'd. */
	boolean isForwardRef = false;

	/** Set when we see actual ID: definition */
	boolean isDefined = true;

	/** List of operands in memory we need to update after seeing def */
	Vector<Address> forwardReferences = null;

	public LabelSymbol(String name) {
		this.name = name;
	}

	public LabelSymbol(String name, int address) {
		this(name);
		this.address = address;
	}

	public LabelSymbol(String name, int address, int offset, boolean forward) {
		this(name);
		isForwardRef = forward;
		if (forward) {
			// if forward reference, then address is address to update
			addForwardReference(address, offset);
		} else {
			this.address = address;
		}
	}

	class Address {
		int ip;
		int offset;

		Address(int ip, int offset) {
			this.ip = ip;
			this.offset = offset;
		}
	}

	public void addForwardReference(int address, int offset) {
		if (forwardReferences == null) {
			forwardReferences = new Vector<Address>();
		}
		forwardReferences.addElement(new Address(address, offset));
	}

	public void resolveForwardReferences(int[] code) {
		isForwardRef = false;
		// need to patch up all references to this symbol
		Vector<Address> opndsToPatch = forwardReferences;
		for (Address addrToPatch : opndsToPatch) {
			/*
			 * System.out.println("updating operand at addr "+
			 * addr+" to be "+getAddress());
			 */
			code[addrToPatch.ip] = code[addrToPatch.ip] | (address << addrToPatch.offset);
			// BytecodeAssembler2.writeInt(code, addrToPatch, address);
		}
	}

	public String toString() {
		String refs = "";
		if (forwardReferences != null) {
			refs = "[refs=" + forwardReferences.toString() + "]";
		}
		return name + "@" + address + refs;
	}
}