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#ifndef ROL_BLOCKOPERATOR_H
#define ROL_BLOCKOPERATOR_H

#include "ROL_LinearOperator.hpp"
#include "ROL_PartitionedVector.hpp"

/** @ingroup func_group
    \class ROL::BlockOperator
    \brief Provides the interface to apply a block operator to a 
           partitioned vector.

    ---
*/

namespace ROL {

template<class Real>
class BlockOperator : public LinearOperator<Real> {

  typedef Vector<Real>               V;    // ROL Vector
  typedef PartitionedVector<Real>    PV;   // Partitioned Vector
  typedef LinearOperator<Real>       OP;   // Linear Operator

  typedef std::vector<Teuchos::RCP<OP> > OpVec;  // Vector (column-stacked matrix) of pointers to operators
  typedef typename OpVec::size_type      uint;   // index type

private:
  
  Teuchos::RCP<OpVec> blocks_;

public:

  BlockOperator( const Teuchos::RCP<OpVec> &blocks ) : blocks_(blocks) {}
  
  virtual void apply( V &Hv, const V &v, Real &tol ) const {
 
    // Downcast to Partitioned Vectors
    PV &Hv_part = Teuchos::dyn_cast<PV>(Hv);
    const PV &v_part = Teuchos::dyn_cast<const PV>(v);
    
    uint nvec1 = v_part.numVectors();
    uint nvec2 = Hv_part.numVectors();
    uint nblks = blocks_->size();

    TEUCHOS_TEST_FOR_EXCEPTION( (nvec1 != nvec2), std::invalid_argument,
                                ">>> ERROR (ROL_BlockOperator, apply): "
                                "Mismatch between input and output number of subvectors.");

    TEUCHOS_TEST_FOR_EXCEPTION( (nblks != nvec1*nvec2 ) , std::invalid_argument, 
                                ">>> ERROR (ROL_BlockOperator, apply): "
                                "Block operator dimension mismatch."); 

    for( uint i=0; i<nvec1; ++i ) {
      
      Teuchos::RCP<V> Hvi = Hv_part.get(i);
      Teuchos::RCP<V> u = Hvi->clone();

      u->zero(); 

      for( uint j=0; j<nvec2; ++j ) {
        uint k = j+nvec1*i;
          (*blocks_)[k]->apply(*u,*v_part.get(j),tol);
          Hvi->plus(*u);
      }
    }
  }  

}; // class BlockOperator


// Simplified Construction for a 2-by-2 block operator
template<class Real>
class BlockOperator2 : public LinearOperator<Real> {

  typedef Vector<Real>               V;    // ROL Vector
  typedef LinearOperator<Real>       OP;   // Linear Operator

private:

  Teuchos::RCP<OP> bkop_;

public:   
  BlockOperator2( Teuchos::RCP<OP> &a11, Teuchos::RCP<OP> &a21,
                  Teuchos::RCP<OP> &a12, Teuchos::RCP<OP> &a22 ) {

    using std::vector;
    using Teuchos::RCP;
    using Teuchos::rcp;

    RCP<vector<RCP<OP> > > ops = rcp( new vector<RCP<OP> > );
    ops->push_back(a11);
    ops->push_back(a21);
    ops->push_back(a12);
    ops->push_back(a22);
            
    bkop_ = rcp( new BlockOperator<Real>(ops) );
  }

  void apply( V &Hv, const V &v, Real &tol ) const {
    bkop_->apply(Hv,v,tol);  
  }
};

} // namespace ROL

#endif // ROL_BLOCKOPERATOR_H
