//
// Created by mfritzsc on 7/12/17.
//

#ifndef TMCAGLWM_RESULT_HPP
#define TMCAGLWM_RESULT_HPP

#include <experimental/optional>
#include <functional>

namespace wm {

using std::experimental::optional;
using std::experimental::nullopt;

// We only ever return a string as an error - so just parametrize
// this over result type T
template <typename T>
struct result {
   char const *e;
   optional<T> t;

   bool is_ok() const { return this->t != nullopt; }
   bool is_err() const { return this->e != nullptr; }

   T unwrap() {
      if (this->e != nullptr) {
         throw std::logic_error(this->e);
      }
      return this->t.value();
   }

   operator T() {
      return this->unwrap();
   }

   char const *unwrap_err() { return this->e; }

   optional<T> ok() const { return this->t; }
   optional<char const *> err() const { return optional<char const *>(this->e); }

   result<T> map_err(std::function<char const *(char const *)> f);
};

template <typename T>
struct result<T> Err(char const *e) {
   return result<T>{e, nullopt};
}

template <typename T>
struct result<T> Ok(T t) {
   return result<T>{nullptr, t};
}

template <typename T>
result<T> result<T>::map_err(std::function<char const *(char const *)> f) {
   if (this->is_err()) {
      return Err<T>(f(this->e));
   }
   return *this;
}

}  // namespace wm

#endif  // TMCAGLWM_RESULT_HPP