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#ifndef MOZC_WIN32_BASE_SURROGATE_PAIR_OBSERVER_H_
#define MOZC_WIN32_BASE_SURROGATE_PAIR_OBSERVER_H_

#include <windows.h>

#include "base/port.h"

namespace mozc {
namespace win32 {

class VirtualKey;

class SurrogatePairObserver {
 public:
  // Return code which represents the expected action of the IME DLL.
  enum ClientActionType {
    // This key event is not a VK_PACKET-related event.
    // The the caller must do the default action.
    DO_DEFAULT_ACTION = 0,
    // This key event is a VK_PACKET-related event.
    // The caller replace the VirtualKey instance with new one which conatins
    // returned ucs4 character code.
    // Then the caller must proceed to do the default action.
    DO_DEFAULT_ACTION_WITH_RETURNED_UCS4,
    // This key event must be consumed silently. In other words, the caller
    // must not send this event to the Mozc server.
    CONSUME_KEY_BUT_NEVER_SEND_TO_SERVER,
    CLIENT_ACTION_LAST = 0xffffffff,
  };

  struct ClientAction {
    ClientAction(ClientActionType type, char32 ucs4)
        : type(type), ucs4(ucs4) {}
    const ClientActionType type;
    const char32 ucs4;
  };

  SurrogatePairObserver();

  ClientAction OnTestKeyEvent(const VirtualKey &virtual_key, bool is_keydown);
  ClientAction OnKeyEvent(const VirtualKey &virtual_key, bool is_keydown);

 private:
  enum ObservationState {
    INITIAL_STATE = 0,
    WAIT_FOR_SURROGATE_HIGH_UP,
    WAIT_FOR_SURROGATE_LOW_DOWM,
    WAIT_FOR_SURROGATE_LOW_UP,
    OBSERVATION_STATE_LAST = 0xffffffff,
  };

  // Returns the expected action of the IME DLL against the given key event.
  ClientAction OnKeyEvent(const VirtualKey &virtual_key, bool is_keydown,
                          bool is_testkey);

  ObservationState state_;
  wchar_t surrogate_high_;
  wchar_t surrogate_low_;

  DISALLOW_COPY_AND_ASSIGN(SurrogatePairObserver);
};

}  // namespace win32
}  // namespace mozc

#endif  // MOZC_WIN32_BASE_SURROGATE_PAIR_OBSERVER_H_