#ifndef EQUATION_H
#define EQUATION_H

#include "Variable.h"
#include "Expression.h"
#include <map>
#include <string>

template<class T>
struct Equation {
  Equation(const Variable<T>& var, Expression<T>* value)
    : _var(var), _value(value) { }

  Variable<T> var() const {
    return _var;
  }
  Variable<T> var(const Variable<T>& var) {
    Variable<T> old_var = _var;
    _var = var;
    return _var;
  }

  Expression<T>* value() const {
    return _value;
  }
  Expression<T>* value(const Expression<T>* value) {
    Expression<T>* old_value = _value;
    _value = value;
    return old_value;
  }

  std::map<std::string, T> solve(const std::map<std::string, T>& curr) {
    std::map<std::string, T> result = curr;
    T last;
    do {
      last = result[_var.name()];
      result[_var.name()] = _value->eval(result);
    } while (last != result[_var.name()]);
    return result;
  }

  private:
  Variable<T> _var;
  Expression<T>* _value;
};

#endif