// DatasetMerger.h

#ifndef dset__DatasetMerger_H
#define dset__DatasetMerger_H

// David Adams
// April 2004
//
// A dataset merger merges a collection of datasets into a
// single dataset. This is an abstract base. Concrete subclasses
// implement strategies for merging.
//
// The state of the merge including the merged dataset is guaranteed
// to change only when the update() method is invoked.
//
// The merger is responsible for managing the merged datasets returned
// as results. These should remain valid at least until another result
// is generated.

#include <string>
#include <iosfwd>
#include <memory>
#include "dataset_base/Dataset.h"
#include "dataset_split/DatasetMergeResult.h"

class XmlElement;

namespace dset {

class DatasetMerger {

private:  // Hidden functions

  // Hide copy and assignment.
  DatasetMerger(const DatasetMerger&);
  DatasetMerger& operator=(const DatasetMerger&);

public:  // Constructors and destructor.

  // Default constructor.
  DatasetMerger();

  // Destructor.
  virtual ~DatasetMerger();

public:  // Virtual methods

  // Validity.
  virtual bool is_valid() const =0;

  // Open.
  virtual bool is_open() const =0;

  // Append a dataset.
  // This dataset should not be deleted before the merge is complete.
  // Returns 0 for success, i.e. the new dataset is accepted.
  // It may still be rejected later.
  virtual int append(const Dataset& dst) =0;

  // Return the result.
  // This should not be blocking--if the result will require a long
  // time to calculate, then this method should quickly return a
  // (consistent) partial result.
  // Result should remain valid until the next call to this method or
  // until the merger is deleted.
  virtual DatasetMergeResult result() =0;

  // Close.
  // Notify merger that all datasets have been merged and it can clean
  // up, i.e. delete temporary results and release their files.
  // Datasets referenced in the current result should not be deleted.
  // Returns 0 for success.
  // Default does nothing and returns success.
  virtual int close() =0;

  // Output stream.
  virtual std::ostream& ostr(std::ostream& str) const =0;

};

}  // end namespace dset

// Free functions.
std::ostream&
operator<<(std::ostream& lhs, const dset::DatasetMerger& rhs);

#endif