#include <petsc/private/taolinesearchimpl.h>

static PetscErrorCode TaoLineSearchView_Unit(TaoLineSearch ls, PetscViewer viewer)
{
  PetscBool isascii;

  PetscFunctionBegin;
  PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERASCII, &isascii));
  if (isascii) PetscCall(PetscViewerASCIIPrintf(viewer, "  Line Search: Unit Step %g.\n", (double)ls->initstep));
  PetscFunctionReturn(PETSC_SUCCESS);
}

/* Take unit step (newx = startx + initstep*step_direction) */
static PetscErrorCode TaoLineSearchApply_Unit(TaoLineSearch ls, Vec x, PetscReal *f, Vec g, Vec step_direction)
{
  PetscFunctionBegin;
  PetscCall(TaoLineSearchMonitor(ls, 0, *f, 0.0));
  ls->step = ls->initstep;
  PetscCall(VecAXPY(x, ls->step, step_direction));
  PetscCall(TaoLineSearchComputeObjectiveAndGradient(ls, x, f, g));
  PetscCall(TaoLineSearchMonitor(ls, 1, *f, ls->step));
  ls->reason = TAOLINESEARCH_SUCCESS;
  PetscFunctionReturn(PETSC_SUCCESS);
}

/*MC
   TAOLINESEARCHUNIT - Line-search type that disables line search and accepts the unit step length every time

  Options Database Keys:
. -tao_ls_stepinit <step> - steplength

   Level: developer

.seealso: `Tao`, `TaoLineSearch`, `TaoLineSearchCreate()`, `TaoLineSearchSetType()`, `TaoLineSearchApply()`
M*/
PETSC_EXTERN PetscErrorCode TaoLineSearchCreate_Unit(TaoLineSearch ls)
{
  PetscFunctionBegin;
  ls->ops->setup   = NULL;
  ls->ops->reset   = NULL;
  ls->ops->monitor = NULL;
  ls->ops->apply   = TaoLineSearchApply_Unit;
  ls->ops->view    = TaoLineSearchView_Unit;
  PetscFunctionReturn(PETSC_SUCCESS);
}