package gve.calc.formula;

import java.util.Hashtable;

 When redefining a variable, the old contents are lost forever. 
public class SingleFallbackEvaluator implements Evaluator {
	private Hashtable vars;
	private Evaluator fbEvaluator;
	private Hashtable functions = new Hashtable();

	
 If this evaluator does not contain a variable,
	  ask it the fallback evaluator.
	  You cannot undefine variables in the fallback evaluator;
	  this Evaluator keeps the fallback unchanged. 
	public SingleFallbackEvaluator(Evaluator fallback) {
		fbEvaluator = fallback;
		vars = new Hashtable();
	}

	
 Note that this copy is shallow with respect to fbEvaluator 
	public Object clone() {
		SingleFallbackEvaluator result = new SingleFallbackEvaluator(fbEvaluator);
		if (vars != null) result.vars = (Hashtable)vars.clone();
		result.functions = (Hashtable)functions.clone();
		return result;
	}

	public void defineVariable(String name,Part value) {
		vars.put(name,value);
	}

	public java.util.Enumeration variables() {
		return new FallbackEnumeration(vars.keys(),fbEvaluator.variables());
	}

	public void undefVariable(String name) {
		vars.remove(name);
	}

	public Part getValue(String identifier) {
		Part o = (Part)vars.get(identifier);
		if (o == null) return fbEvaluator.getValue(identifier);
		return o;
	}

	public void setValue(String name,Part value) {
		vars.put(name,value);
	}

	public String toString() {
		return vars.toString();
	}

	public void dump() {
		java.util.Enumeration keys = vars.keys();
		while (keys.hasMoreElements()) {
			Object key = keys.nextElement();
			System.out.println("---key "+key);
			Object val = vars.get(key);
			if (val instanceof Part) ((Part)val).dump(1);
			else System.out.println(val);
		}
		System.out.println("Fallback evaluator contains:");
		fbEvaluator.dump();
	}

	public Part call(String funcname,Part args) {
		Function f = (Function)functions.get(funcname);
		if (f == null) return fbEvaluator.call(funcname,args);
		return f.call(funcname,args,this);
	}

	public void setFunction(String funcname,Function f) {
		functions.put(funcname,f);
	}

	public boolean isFunction(String funcname) {
		if (functions.get(funcname) != null) return true;
		return fbEvaluator.isFunction(funcname);
	}
}