#ifndef ROOT_THaHelicityDet
#define ROOT_THaHelicityDet

////////////////////////////////////////////////////////////////////////
//
// THaHelicityDet
//
// Abstract base class for a beam helicity "detector".
// Typically, this type of detector will be part of a beam apparatus.
// 
// authors: V. Sulkosky and R. Feuerbach, Jan 2006
// Changed to an abstract base class. Ole Hansen, Aug 2006.
//
////////////////////////////////////////////////////////////////////////

#include "THaDetector.h"

class THaHelicityDet :  public THaDetector {
  
public:

  enum EHelicity { kMinus = -1, kUnknown, kPlus };

  virtual ~THaHelicityDet();

  virtual void       Clear( Option_t* opt="" ) 
  { THaDetector::Clear(opt); fHelicity = kUnknown; }
  virtual EHelicity  GetHelicity()   const { return fHelicity; }
  virtual Bool_t     HelicityValid() const { return (fHelicity != kUnknown); }

  virtual const char* GetDBFileName() const;
  virtual void        MakePrefix();

  THaHelicityDet() {}  // For ROOT I/O only

protected:

  //Only derived classes may construct me
  THaHelicityDet( const char* name, const char* description,
		  THaApparatus* a = NULL);

  EHelicity fHelicity;  // Beam helicity. fHelicity = fSign * decoded_helicity
  Int_t     fSign;      // Overall sign of beam helicity. Default 1.

  virtual Int_t DefineVariables( EMode mode = kDefine );
  virtual Int_t ReadDatabase( const TDatime& date );

  ClassDef(THaHelicityDet,1)     // ABC for a beam helicity detector
};

#endif