//# ArrayPosIter.h: Iterate an IPosition through the shape of an Array
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//# $Id$

#ifndef CASA_ARRAYPOSITER_2_H
#define CASA_ARRAYPOSITER_2_H

//# Change the following to a forward declare?
#include "IPosition.h"

namespace casacore { //# NAMESPACE CASACORE - BEGIN

//# Forward Declarations
class ArrayBase;


// <summary> Iterate an IPosition through the shape of an Array </summary>
// <reviewed reviewer="UNKNOWN" date="before2004/08/25" tests="" demos="">
// </reviewed>

// <synopsis>
// ArrayPositionIterator manipulates an IPosition "cursor" through some
// volume defined by an origin and shape. This position can in turn be
// used to index into, or otherwise define a position in, an Array. Normally
// users won't use this class directly, rather they will use an ArrayIterator,
// VectorIterator or MatrixIterator object, which in turn uses this class.
// ArrayPositionIterator is also used in the implementation of Array.
//
// <srcblock>
// template<class T> void verySlowArrayCopy(Array<T> &to, const Array<T> &from)
// {
//     if (! to.conform(from)) {
//        // throw some error
//     }
//     ArrayPositionIterator toiter(to.shape(), to.origin(),0);
//     ArrayPositionIterator fromiter(from.shape(), from.origin(),0);
//     // If to.origin() == from.origin() we only need one iterator
//     // or we could offset positions by the difference in origins.
//     // The "0" means we are stepping by scalars.
//     while (! toiter.pastEnd()) {    // we know arrays conform
//         to(toiter.pos()) = fromiter(fromiter.pos());
//         toiter.next(); fromiter.next();
//     }
// }
// </srcblock>
//
// Iteration can be done by any combination of axes, but it can only be
// done for full axes.
// <br>The iteration step always "fills up" its dimensionality.
// E.g., if we are stepping through a cube by matrices, the matrix completely
// fills up the plane.
// Casacore class ArrayLattice in the lattices
// package can be used to iterate with partial volumes.
//
// <p>
// ArrayPositionIterator also serves as the base class of ArrayIterator.
// Function <src>makeIterator</src> in class ArrayBase can be used to make an
// ArrayIterator without having to know the template type. Function
// <src>getArray</src> in this class can be used to obtain the current
// contents of the cursor as an ArrayBase object.
// </synopsis>

class ArrayPositionIterator
{
public:
    // Define the shape and origin of the volume the cursor will step
    // through. Also define the dimensionality of the step. byDim==0 implies
    // we are stepping by scalars (i.e. every element), byDim==1 implies that
    // we are stepping by vector, ==2 by matrices, and so on.
    // If uses the first byDim axes as the cursor volume and it steps
    // through the remaining axes.
    // <group>
    ArrayPositionIterator(const IPosition &shape, const IPosition &origin,
			  size_t byDim);
    ArrayPositionIterator(const IPosition &shape,
			  size_t byDim);
    // </group>

    // Step through an array using the given axes.
    // The axes can be given in two ways:
    // <ol>
    // <li>axesAreCursor=true means that the axes form the cursor axes.
    //     The remaining axes will form the iteration axes.
    //     This is the default.
    // <li>axesAreCursor=false means the opposite.
    //     In this case the iteration axes can be given in any order.
    // </ol>
    // E.g. when using iteration axes 2,0 for an array with shape [5,3,7], each
    // iteration step returns a cursor (containing the data of axis 1).
    // During the iteration axis 2 will vary most rapidly (as it was
    // given first).
    // <br>E.g. for a shape of [3,4,5,6] and cursor axes [2,0], the cursor size
    // is [3,5] (axes 0 and 2), while the iteration is done over axes 1 and 3
    // (1 the fastest varying one).
    ArrayPositionIterator(const IPosition &shape,
			  const IPosition &axes,
			  bool axesAreCursor=true);

    virtual ~ArrayPositionIterator() {};

    // Reset the cursor to the beginning of the volume.
    // <group>
    virtual void reset();
    void origin()
      { reset(); }
    // </group>

    // Returns true of the cursor is at the origin.
    bool atStart() const;

    // Returns true if the cursor has moved past the end of its volume.
    bool pastEnd() const;

    // Return the position of the cursor.
    // This include all axes
    const IPosition &pos() const {return Cursor;}

    // Return the end position of the cursor.
    IPosition endPos() const;

    // Advance the cursor to its next position.
    virtual void next();

    // Set the cursor to the given position.
    // The position can only contain the iteration axes or it can be the full
    // position.
    // <br>In the first case the position must to be given in the order
    // of the iteration axes as given in the constructor.
    // In the latter case the position must be given in natural order
    // (as given by function <src>pos</src> and only the cursor axes are taken
    // into account.
    virtual void set (const IPosition& cursorPos);

    // What is the dimensionality of the volume we are iterating through?
    size_t ndim() const;

    // Return the iteration axes.
    const IPosition &iterAxes() const {return iterationAxes;}

    // Return the cursor axes.
    const IPosition &cursorAxes() const {return cursAxes;}

    // Get the array in the cursor.
    // This is only implemented in the derived ArrayIterator class.
    // By default it throws an exception.
    virtual ArrayBase& getArray();

protected:
    // Advance cursor to its next position and tell which dimension stepped.
    size_t nextStep();
    // What is the dimensionality of the "step" the cursor takes, i.e.
    // 0 for scalars, 1 for vector, ....
    size_t dimIter() const {return cursAxes.nelements();}

private:
    // Setup the object for the constructor.
    // <group>
    void setup(size_t byDim);
    void setup(const IPosition &axes, bool axesAreCursor);
    // </group>

    //# We should probably have mf's for getting at Start,Shape and End.
    IPosition Start, Shape, End, Cursor;
    bool atOrBeyondEnd;
    IPosition cursAxes, iterationAxes;
};

// Dimensionality of the array we are iterating through.
inline size_t ArrayPositionIterator::ndim() const
{
    return Start.nelements();
}

// We are at the "end" if we cannot advance any more.
inline bool ArrayPositionIterator::pastEnd() const
{
    return atOrBeyondEnd;
}


} //# NAMESPACE CASACORE - END

#endif