/* -*- mode: C -*-  */
/* 
   IGraph library.
   Copyright (C) 2014  Gabor Csardi <csardi.gabor@gmail.com>
   334 Harvard street, Cambridge, MA 02139 USA
   
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.
   
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.
   
   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 
   02110-1301 USA

*/

#include "igraph_interface.h"
#include "igraph_interrupt_internal.h"
#include "igraph_vector_ptr.h"
#include "igraph_iterators.h"
#include "igraph_adjlist.h"
#include "igraph_stack.h"

/**
 * \function igraph_get_all_simple_paths
 * List all simple paths from one source
 *
 * A path is simple, if its vertices are unique, no vertex
 * is visited more than once.
 *
 * </para><para>
 * Note that potentially there are exponentially many
 * paths between two vertices of a graph, and you may
 * run out of memory when using this function, if your
 * graph is lattice-like.
 *
 * </para><para>
 * This function currently ignored multiple and loop edges.
 * \param graph The input graph.
 * \param res Initialized integer vector, all paths are
 *        returned here, separated by -1 markers. The paths
 *        are included in arbitrary order, as they are found.
 * \param from The start vertex.
 * \param to The target vertices.
 * \param mode The type of the paths to consider, it is ignored
 *        for undirectred graphs.
 * \return Error code.
 *
 * Time complexity: O(n!) in the worst case, n is the number of
 * vertices.
 */

int igraph_get_all_simple_paths(const igraph_t *graph,
				igraph_vector_int_t *res,
				igraph_integer_t from,
				const igraph_vs_t to,
				igraph_neimode_t mode) {

  igraph_integer_t no_nodes=igraph_vcount(graph);
  igraph_vit_t vit;
  igraph_bool_t toall=igraph_vs_is_all(&to);
  igraph_vector_char_t markto;
  igraph_lazy_adjlist_t adjlist;
  igraph_vector_int_t stack;
  igraph_vector_char_t added;
  igraph_vector_int_t nptr;
  int iteration;

  if (from < 0 || from >= no_nodes) {
    IGRAPH_ERROR("Invalid starting vertex", IGRAPH_EINVAL);
  }
  
  if (!toall) {
    igraph_vector_char_init(&markto, no_nodes);
    IGRAPH_FINALLY(igraph_vector_char_destroy, &markto);
    IGRAPH_CHECK(igraph_vit_create(graph, to, &vit));
    IGRAPH_FINALLY(igraph_vit_destroy, &vit);
    for (; !IGRAPH_VIT_END(vit); IGRAPH_VIT_NEXT(vit)) {
      VECTOR(markto)[ IGRAPH_VIT_GET(vit) ] = 1;
    }
    igraph_vit_destroy(&vit);
    IGRAPH_FINALLY_CLEAN(1);
  }

  IGRAPH_CHECK(igraph_vector_char_init(&added, no_nodes));
  IGRAPH_FINALLY(igraph_vector_char_destroy, &added);
  IGRAPH_CHECK(igraph_vector_int_init(&stack, 100));
  IGRAPH_FINALLY(igraph_vector_int_destroy, &stack);
  IGRAPH_CHECK(igraph_lazy_adjlist_init(graph, &adjlist, mode, 
					/*simplify=*/ 1));  
  IGRAPH_FINALLY(igraph_lazy_adjlist_destroy, &adjlist);
  IGRAPH_CHECK(igraph_vector_int_init(&nptr, no_nodes));
  IGRAPH_FINALLY(igraph_vector_int_destroy, &nptr);

  igraph_vector_int_clear(res);

  igraph_vector_int_clear(&stack);
  igraph_vector_int_push_back(&stack, from);
  VECTOR(added)[from] = 1;
  while (!igraph_vector_int_empty(&stack)) {
    int act=igraph_vector_int_tail(&stack);
    igraph_vector_t *neis=igraph_lazy_adjlist_get(&adjlist, act);
    int n=igraph_vector_size(neis);
    int *ptr=igraph_vector_int_e_ptr(&nptr, act);

    if (iteration == 0) {
      IGRAPH_ALLOW_INTERRUPTION();
    }

    /* Search for a neighbor that was not yet visited */
    igraph_bool_t any=0;
    int nei;
    while (!any && (*ptr) <n) {
      nei = (int) VECTOR(*neis)[(*ptr)];
      any = !VECTOR(added)[nei];
      (*ptr) ++;
    }
    if (any) {
      /* There is such a neighbor, add it */
      IGRAPH_CHECK(igraph_vector_int_push_back(&stack, nei));
      VECTOR(added)[nei] = 1;
      /* Add to results */
      if (toall || VECTOR(markto)[nei]) {
	IGRAPH_CHECK(igraph_vector_int_append(res, &stack));
	IGRAPH_CHECK(igraph_vector_int_push_back(res, -1));
      }
    } else {
      /* There is no such neighbor, finished with the subtree */
      int up=igraph_vector_int_pop_back(&stack);
      VECTOR(added)[up] = 0;
      VECTOR(nptr)[up] = 0;
    }

    iteration++;
    if (iteration >= 10000) {
      iteration = 0;
    }
  }

  igraph_vector_int_destroy(&nptr);
  igraph_lazy_adjlist_destroy(&adjlist);
  igraph_vector_int_destroy(&stack);
  igraph_vector_char_destroy(&added);
  IGRAPH_FINALLY_CLEAN(4);

  if (!toall) {
    igraph_vector_char_destroy(&markto);
    IGRAPH_FINALLY_CLEAN(1);
  }

  return 0;
}