/* Copyright (c) 1997-2024
   Ewgenij Gawrilow, Michael Joswig, and the polymake team
   Technische Universität Berlin, Germany
   https://polymake.org

   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, or (at your option) any
   later version: http://www.gnu.org/licenses/gpl.txt.

   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.
--------------------------------------------------------------------------------
*/

#include "polymake/client.h"
#include "polymake/Array.h"
#include "polymake/Set.h"
#include "polymake/hash_set"
#include <sstream>

namespace polymake { namespace topaz {

BigObject suspension(BigObject p_in, Int k, OptionSet options)
{
   Array<Set<Int>> C = p_in.give("FACETS");
   const Int n_v = p_in.give("N_VERTICES");
   Array<std::string> apex_labels;

   if (options["apex_labels"] >> apex_labels) {
      if (k==0) {
         k = apex_labels.size();
         if (k%2)
            throw std::runtime_error("suspension - must specify an even number of apex labels");
         if (!k)
            throw std::runtime_error("suspension - empty apex label list");
         k /= 2;
      } else if (k*2 != apex_labels.size())
         throw std::runtime_error("suspension - wrong number of apex labels");
   } else {
      assign_max(k, 1);
   }

   const sequence new_V(n_v,2*k);
   const Int orig_size = C.size();
   C.resize(orig_size * (1L << k));

   sequence::const_iterator s_it = new_V.begin();
   for (Int i = 0; i < k; ++i) {
      Array<Set<Int>> SUS(C.size());
                
      const Int v1 = *s_it;     ++s_it;
      const Int v2 = *s_it;     ++s_it;
      for (Int j = 0, j_limit = orig_size * (1L << i); j < j_limit; ++j) {
         SUS[2*j] = C[j]+v1;
         SUS[2*j+1] = C[j]+v2;
      }
      C = SUS;
   }
   BigObject p_out("SimplicialComplex");
   p_out.set_description() << k << "-suspension of " << p_in.name() << endl;
   p_out.take("FACETS") << C;

   if (!options["no_labels"]) {
      Array<std::string> L = p_in.give("VERTEX_LABELS");
      hash_set<std::string> old_L(L.begin(), L.end());

      if (!apex_labels.empty()) {
         for (auto l = entire(apex_labels); !l.at_end(); ++l)
            if (! old_L.insert(*l).second)
               throw std::runtime_error("suspension - apex labels not unique");

         L.append(k*2, apex_labels.begin());
      } else {
         Int gen = 0;
         std::string gen_suffix="";
         bool unique;
         L.resize(n_v+2*k);
         do {
            unique = true;
            for (Int count = 0; count < 2*k; ++count) {
               std::ostringstream label;
               label << "apex" << gen_suffix;
               if (k>1) label << '_' << count/2;
               label << (count%2 ? '-' : '+');
               std::string l=label.str();
               if (old_L.find(l) != old_L.end()) {
                  ++gen;
                  label.str("");
                  label << '_' << gen;
                  gen_suffix=label.str();
                  unique=false;
                  break;
               }
               L[n_v+count] = l;
            }
         } while (!unique);
      }

      p_out.take("VERTEX_LABELS") << L;
   }

   return p_out;
}

UserFunction4perl("# @category Producing a new simplicial complex from others"
                  "# Produce the __//k//-suspension__ over a given simplicial complex."
                  "# @param SimplicialComplex complex"
                  "# @param Int k default value is 1"
                  "# @option Array<String> labels for the apices."
                  "#  By default apices are labeled with ''apex_0+'', ''apex_0-'', ''apex_1+'', etc."
                  "#  If one of the specified labels already exists, a unique one is made"
                  "#  by appending ''_i'' where //i// is some small number."
                  "# @option Bool no_labels Do not create [[VERTEX_LABELS]]. default: 0"
                  "# @return SimplicialComplex"
                  "# @example The suspension of a 1-sphere is a 2-sphere:"
                  "# > $s = new SimplicialComplex(FACETS=>[[0,1],[1,2],[2,0]]);"
                  "# > print suspension($s)->HOMOLOGY;"
                  "# | ({} 0)"
                  "# | ({} 0)"
                  "# | ({} 1)",
                  &suspension, "suspension(SimplicialComplex; $=0, { apex_labels => undef, no_labels => 0 })");
} }

// Local Variables:
// mode:C++
// c-basic-offset:3
// indent-tabs-mode:nil
// End:
