package EDU.gac.max.MC97.S97.c3;

import java.util.Hashtable;
import java.util.Enumeration;
import EDU.gac.max.MC97.S97.compiler_support.Register;

abstract class Proc{
  public abstract String gen();
}

class MainProc extends Proc{
  Stmt body;

  MainProc(Stmt theBody){
    body = theBody;
  }

  public String gen(){
    Hashtable regsToSave = new Hashtable();
    String bodyCode = body.gen(regsToSave);
    return prolog(regsToSave) + bodyCode + epilog(regsToSave);
  }

  // The two calls below to the Hashtable's keys method need to return
  // enumerations that follow the same order, or registers will get restored
  // into one another.  This seems like a reasonable property to assume, but
  // the official 1.0.2 API documentation for Hashtable doesn't say anything
  // about it, so I'm on thin ice -- cross your fingers.

  private String prolog(Hashtable regsToSave){
    StringBuffer theProlog = new StringBuffer("main:\n");
    if(regsToSave.size() > 0)
      theProlog.append("\tsubu $sp, $sp, " + (4 * regsToSave.size()) + "\n");
    Enumeration e = regsToSave.keys();
    for(int offset = 0; e.hasMoreElements(); offset += 4){
      theProlog.append("\tsw " + (Register) (e.nextElement()) + ", "
                        + offset + "($sp)\n");
    }
    return theProlog.toString();
  }

  private String epilog(Hashtable regsToSave){
    StringBuffer theEpilog = new StringBuffer("\tli $v0, 0\n");
    Enumeration e = regsToSave.keys();
    int offset;
    for(offset = 0; e.hasMoreElements(); offset += 4){
      theEpilog.append("\tlw " + (Register) (e.nextElement()) + ", "
                        + offset + "($sp)\n");
    }
    if(offset > 0)
      theEpilog.append("\taddu $sp, $sp, " + offset + "\n");
    theEpilog.append("\tj $ra\n");
    return theEpilog.toString();
  }
}