// **********************************************************************
// The SymTab class implements a symbol table, which is a LinkedList
// of Hashtables, each containing zero or more Syms.
//
// Public Methods
// ==============
//
// constructor
// -----------
// SymTab()            -- initialize the table to be empty (i.e., to
//                        be a LinkedList containing one, empty Hashtable)
//
// modifiers
// ---------
// void insert(Sym sym)  -- add sym to the first table in the LinkedList
//                          (error if the LinkedList is empty or if 
//                          there is already a symbol with the
//                          same name)
//
// void addHashtab()     -- add a new, empty Hashtable to the front of
//                          the LinkedList
//
// void removeHashtab()  -- remove the Hashtable from the front of
//                          the LinkedList (error if the LinkedList is
//                          already empty)
//
// other operations
// ----------------
// Sym localLookup(String k)  -- if there is a symbol with the given name
//                               in the first hashtable in the LinkedList,
//                               then return it;
//                               otherwise, return null
// Sym globalLookup(String k) -- if there is a symbol with the given name
//                               in ANY hashtable in the LinkedList,
//                               then return the first such Sym;
//                               otherwise, return null
// void print(PrintWriter p)  -- print all of the Hashtables in the
//                               LinkedList, one per line, to the given
//                               PrintWriter

import java.io.*;
import java.util.*;
                                               
class SymTab {
    /*** private fields ***/
    LinkedList myList; // the LinkedList of hashtables

    /*** public methods ***/

    // **********************************************************************
    // constructor
    // **********************************************************************
    public SymTab() {
	myList = new LinkedList();
	addHashtab();
    }

    // **********************************************************************
    // insert
    // **********************************************************************
    public void insert(Sym sym)
	throws DuplicateException, EmptySymTabException
{
	Hashtable tab;

	if (myList.size() == 0) throw new EmptySymTabException();
	if (localLookup(sym.name()) != null) throw new DuplicateException();
	try {
	    tab = (Hashtable)(myList.getFirst());
	    tab.put(sym.name(), sym);
	} catch (NoSuchElementException ex) {
	    // shouldn't get here
	    System.err.println("unexpected NoSuchElementException in SymTab.insert");
	    System.exit(-1);
	}
    }

    // **********************************************************************
    // addHashtab
    // **********************************************************************
    public void addHashtab() {
	myList.addFirst(new Hashtable());
    }

    // **********************************************************************
    // removeHashtab
    // **********************************************************************
    public void removeHashtab() throws EmptySymTabException {
	try {
	    myList.removeFirst();
	} catch (NoSuchElementException ex) {
	    throw new EmptySymTabException();
	}

    }

    // **********************************************************************
    // localLookup
    // **********************************************************************
    public Sym localLookup(String str) {
	Hashtable tab;

	if (myList.size() == 0) return null;
	try {
	    tab = (Hashtable)(myList.getFirst());
	    return (Sym)(tab.get(str));
	} catch (NoSuchElementException ex) {
	    // shouldn't get here
	    System.err.println("unexpected NoSuchElementException in SymTab.insert");
	    System.exit(-1);
	    return null; // compiler requires a return here
	}
    }

    // **********************************************************************
    // globalLookup
    // **********************************************************************
    public Sym globalLookup(String str) {
	Hashtable tab;
	Sym tmp;
	Iterator it = myList.iterator();
	try {
	    while (it.hasNext()) {
		tab = (Hashtable)(it.next());
		tmp = (Sym)(tab.get(str));
		if (tmp != null) return tmp;
	    }
	} catch (NoSuchElementException ex) {
	    // shouldn't get here
	    System.err.println("unexpected NoSuchElementException in SymTab.globalLookup");
	    System.exit(-1);
	}
	return null;
    }

    // **********************************************************************
    // print
    // **********************************************************************
    public void print(PrintWriter p) {
	Hashtable tab;
	Iterator it = myList.iterator();

	try {
	    while (it.hasNext()) {
		tab = (Hashtable)(it.next());
		p.println(tab.toString());
	    }
	} catch (NoSuchElementException ex) {
	    // shouldn't get here
	    System.err.println("unexpected NoSuchElementException in SymTab.print");
	    System.exit(-1);
	}
    }

}