/// \file ROOT/RHistBinIter.hxx
/// \ingroup HistV7
/// \author Axel Naumann <axel@cern.ch>
/// \date 2015-08-07
/// \warning This is part of the ROOT 7 prototype! It will change without notice. It might trigger earthquakes. Feedback
/// is welcome!

/*************************************************************************
 * Copyright (C) 1995-2015, Rene Brun and Fons Rademakers.               *
 * All rights reserved.                                                  *
 *                                                                       *
 * For the licensing terms see $ROOTSYS/LICENSE.                         *
 * For the list of contributors see $ROOTSYS/README/CREDITS.             *
 *************************************************************************/

#ifndef ROOT7_RHistBinIter
#define ROOT7_RHistBinIter

#include "ROOT/RIndexIter.hxx"

namespace ROOT {
namespace Experimental {
namespace Detail {

/**
\class RHistBinRef
Represents a bin reference. Value of the bin iteration.

Provides access to bin content, bin geometry (from, to, center), and statistics
(for instance higher moments) associated to the bin.
*/

template <class HISTIMPL>
class RHistBinRef {
public:
   using HistImpl_t = HISTIMPL;
   using CoordArray_t = typename HISTIMPL::CoordArray_t;
   using Weight_t = typename HISTIMPL::Weight_t;
   using HistBinStat_t = decltype(((HISTIMPL *)0x123)->GetStat().GetView(1));

private:
   size_t fIndex{0}; ///< Bin index
   HistImpl_t *fHist{nullptr}; ///< The bin's histogram.
   HistBinStat_t fStatView;

public:
   /// Construct from a histogram.
   RHistBinRef(HistImpl_t &hist, size_t idx): fIndex(idx), fHist(&hist), fStatView(hist.GetStat().GetView(idx)) {}

   /// \{
   /// \name Statistics operations
   /// Get the bin content (or reference to it, for non-const HistImpl_t).
   auto GetContent() { return fStatView.GetContent(); }

   /// Get the bin uncertainty.
   double GetUncertainty() const { return fStatView.GetUncertainty(); }

   /// Get a (const, for const HistImpl_t) reference to the bin-view of the
   /// histogram statistics (uncertainty etc).
   HistBinStat_t GetStat() const { return fStatView; }
   /// \}

   /// \{
   /// \name Bin operations
   /// Get the bin center as an array over all dimensions.
   CoordArray_t GetCenter() const { return fHist->GetBinCenter(fIndex); }

   /// Get the bin lower edge as an array over all dimensions.
   CoordArray_t GetFrom() const { return fHist->GetBinFrom(fIndex); }

   /// Get the bin upper edge as an array over all dimensions.
   CoordArray_t GetTo() const { return fHist->GetBinTo(fIndex); }
   /// \}
};

/**
 \class RHistBinPtr
 Points to a histogram bin (or actually a `RHistBinRef`).
 */
template <class HISTIMPL>
class RHistBinPtr {
public:
   using Ref_t = RHistBinRef<HISTIMPL>;

   const Ref_t &operator->() const noexcept { return fRef; }

private:
   Ref_t fRef; ///< Underlying bin reference
};

/**
 \class RHistBinIter
 Iterates over the bins of a RHist or RHistImpl.
 */

template <class HISTIMPL>
class RHistBinIter: public Internal::RIndexIter<RHistBinRef<HISTIMPL>, RHistBinPtr<HISTIMPL>> {
public:
   using Ref_t = RHistBinRef<HISTIMPL>;
   using Ptr_t = RHistBinPtr<HISTIMPL>;

private:
   using IndexIter_t = Internal::RIndexIter<RHistBinRef<HISTIMPL>, RHistBinPtr<HISTIMPL>>;

   HISTIMPL &fHist; ///< The histogram we iterate over.

public:
   /// Construct a RHistBinIter from a histogram.
   RHistBinIter(HISTIMPL &hist): IndexIter_t(0), fHist(hist) {}

   /// Construct a RHistBinIter from a histogram, setting the current index.
   RHistBinIter(HISTIMPL &hist, size_t idx): IndexIter_t(idx), fHist(hist) {}

   ///\{
   ///\name Value access
   Ref_t operator*() const noexcept { return Ref_t{fHist, IndexIter_t::GetIndex()}; }

   Ptr_t operator->() const noexcept { return Ptr_t{*this}; }
   ///\}
};

} // namespace Detail
} // namespace Experimental
} // namespace ROOT

#endif