media_cas_proxy_sdk/util/error_space.h

////////////////////////////////////////////////////////////////////////////////
// Copyright 2017 Google LLC.
//
// This software is licensed under the terms defined in the Widevine Master
// License Agreement. For a copy of this agreement, please contact
// widevine-licensing@google.com.
////////////////////////////////////////////////////////////////////////////////

#ifndef UTIL_ERROR_SPACE_H_
#define UTIL_ERROR_SPACE_H_

#include <string>

namespace widevine {
namespace util {

class ErrorSpace {
 public:
  std::string SpaceName() const { return space_name_func_(this); }
  std::string String(int code) const { return code_to_string_func_(this, code); }

 protected:
  // typedef instead of using statements for SWIG compatibility.
  typedef std::string (*SpaceNameFunc)(const ErrorSpace* space);
  typedef std::string (*CodeToStringFunc)(const ErrorSpace* space, int code);
  constexpr ErrorSpace(SpaceNameFunc space_name_func,
                       CodeToStringFunc code_to_string_func)
      : space_name_func_(space_name_func),
        code_to_string_func_(code_to_string_func) {}

 private:
  const SpaceNameFunc space_name_func_;
  const CodeToStringFunc code_to_string_func_;
};

// Manages creation of error space subclasses.
template <typename T>
class ErrorSpaceImpl : public ErrorSpace {
 public:
  constexpr ErrorSpaceImpl()
      : ErrorSpace(&ErrorSpaceImpl::SpaceNameImpl,
                   &ErrorSpaceImpl::CodeToStringImpl) {}

  // Returns the canonical instance of the `T` error space.
  static constexpr const T* Get();

 private:
  // These functions adapt the stateful implementation that takes a space
  // pointer to stateless static methods, so that clients of ErrorSpaceImpl are
  // safe to have constexpr global instances.
  static std::string SpaceNameImpl(const ErrorSpace* /*space*/) {
    return T::space_name();
  }

  static std::string CodeToStringImpl(const ErrorSpace* /*space*/, int code) {
    return T::code_to_string(code);
  }
};

namespace internal {

// Provides a global constexpr instance of the error space `T`.
// We need the indirection because ErrorSpaceImpl can't declare constexpr
// instances of T since it is not yet fully declared.
template <typename T>
struct ErrorSpaceInstance {
  static constexpr T value = {};
};

template <typename T>
constexpr T ErrorSpaceInstance<T>::value;

}  // namespace internal

template <typename T>
constexpr const T* ErrorSpaceImpl<T>::Get() {
  return &internal::ErrorSpaceInstance<T>::value;
}

}  // namespace util
}  // namespace widevine

#endif  // UTIL_ERROR_SPACE_H_