#pragma once

#include "drake/common/default_scalars.h"
#include "drake/common/drake_copyable.h"
#include "drake/systems/analysis/dense_output.h"

namespace drake {
namespace systems {

/// A DenseOutput class interface extension, geared towards step-wise
/// construction procedures. Outputs of this kind are to be built
/// incrementally by means of discrete updates that extend its domain.
/// Nature of an update remains implementation specific.
///
/// To allow for update rectification (i.e. drop and replacement), in case it
/// fails to meet certain criteria (e.g. not within tolerances), construction
/// can be deferred to a consolidation step. In between consolidations, updates
/// can be rolled back (i.e. discarded) one by one on a last-input-first-output
/// basis. Implementations are thus encouraged to keep recent updates in a light
/// weight form, deferring heavier computations and construction of a better
/// suited representation for evaluation. As such, evaluation is bound to
/// succeed only after consolidation.
///
/// @tparam_default_scalar
template <typename T>
class StepwiseDenseOutput : public DenseOutput<T> {
 public:
  DRAKE_NO_COPY_NO_MOVE_NO_ASSIGN(StepwiseDenseOutput)

  ~StepwiseDenseOutput() override = default;

  /// Rolls back (drops) the last update.
  /// @remarks This process is irreversible.
  /// @pre Updates have taken place since instantiation or last
  ///      consolidation (via Consolidate()).
  /// @throws std::exception if any of the preconditions is not met.
  virtual void Rollback() = 0;

  /// Consolidates latest updates.
  ///
  /// All updates since last call or construction are put into a form
  /// that is suitable for evaluation.
  ///
  /// @remarks This process is irreversible.
  /// @pre Updates have taken place since instantiation or last
  ///      consolidation.
  /// @post The extents covered by updates since instantiation or
  ///       last consolidation can be evaluated (via Evaluate()).
  /// @post Time extents covered by updates can be evaluated
  ///       (via start_time()/end_time()).
  /// @throws std::exception if any of the preconditions is not met.
  virtual void Consolidate() = 0;

 protected:
  StepwiseDenseOutput() = default;
};

}  // namespace systems
}  // namespace drake

DRAKE_DECLARE_CLASS_TEMPLATE_INSTANTIATIONS_ON_DEFAULT_SCALARS(
    class drake::systems::StepwiseDenseOutput)
