package kr.pe.acet.interpreter;

import java.util.Map;
import java.util.Stack;

public class Evaluator implements Expression{

	private Expression syntaxTree;
	
	
	public Evaluator(String expression) {
		Stack<Expression> expressionStack = new Stack<Expression>();
		
		for(String token : expression.split(" ")){
			if(token.equals("+")){
				Expression subExpression = new Plus(expressionStack.pop(), expressionStack.pop());
				expressionStack.push(subExpression);
			}else if(token.equals("-")){
				Expression right = expressionStack.pop();				
				Expression left = expressionStack.pop();
				Expression subExpression = new Minus(left, right);
				expressionStack.push(subExpression);
			}else{
				expressionStack.push(new Variable(token));
			}
		}
		syntaxTree = expressionStack.pop();
		
	}

	@Override
	public int interpret(Map<String, Expression> context) {
		return syntaxTree.interpret(context);
	}

}