/*
  simple-spacer-scheme.cc -- implement Simple_spacer

  source file of the GNU LilyPond music typesetter

  (c) 2005--2007 Han-Wen Nienhuys <hanwen@xs4all.nl>
*/

#include <cstdio>

#include "paper-column.hh"
#include "spring.hh"
#include "warn.hh"
#include "simple-spacer.hh"

LY_DEFINE (ly_solve_spring_rod_problem, "ly:solve-spring-rod-problem",
	   4, 1, 0, (SCM springs, SCM rods, SCM length, SCM ragged),
	   "Solve a spring and rod problem for @var{count} objects, that"
	   " are connected by @var{count}-1 @var{springs}, and an arbitrary"
	   " number of @var{rods}.  @var{count} is implicitly given by"
	   " @var{springs} and @var{rods}.  The @var{springs} argument has"
	   " the format @code{(ideal, inverse_hook)} and @var{rods} is of"
	   " the form @code{(idx1, idx2, distance)}.\n"
	   "\n"
	   "@var{length} is a number, @var{ragged} a boolean.\n"
	   "\n"
	   "The function returns a list containing the force (positive for"
	   " stretching, negative for compressing and @code{#f} for"
	   " non-satisfied constraints) followed by @var{spring-count}+1"
	   " positions of the objects.")
{
  int len = scm_ilength (springs);
  if (len == 0)
    return scm_list_2 (scm_from_double (0.0), scm_from_double (0.0));

  SCM_ASSERT_TYPE (len >= 0, springs, SCM_ARG1, __FUNCTION__, "list of springs");
  SCM_ASSERT_TYPE (scm_ilength (rods)  > 0, rods, SCM_ARG1, __FUNCTION__, "list of rods");
  LY_ASSERT_TYPE (scm_is_number, length, 3);

  bool is_ragged = ragged == SCM_BOOL_T;
  Simple_spacer spacer;
  for (SCM s = springs; scm_is_pair (s); s = scm_cdr (s))
    {
      Real ideal = scm_to_double (scm_caar (s));
      Real inv_hooke = scm_to_double (scm_cadar (s));

      Spring sp (ideal, 0.0);
      sp.set_inverse_compress_strength (inv_hooke);
      sp.set_inverse_stretch_strength (inv_hooke);

      spacer.add_spring (sp);
    }

  for (SCM s = rods; scm_is_pair (s); s = scm_cdr (s))
    {
      SCM entry = scm_car (s);
      int l = scm_to_int (scm_car (entry));
      int r = scm_to_int (scm_cadr (entry));
      entry = scm_cddr (entry);

      Real distance = scm_to_double (scm_car (entry));
      spacer.add_rod (l, r, distance);
    }

  spacer.solve (scm_to_double (length), is_ragged);

  vector<Real> posns = spacer.spring_positions ();

  SCM force_return = spacer.fits () ? scm_from_double (spacer.force ()) : SCM_BOOL_F;

  SCM retval = SCM_EOL;
  for (vsize i = posns.size (); i--;)
    retval = scm_cons (scm_from_double (posns[i]), retval);

  retval = scm_cons (force_return, retval);
  return retval;
}
