standard.hh

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#pragma once

#include <set>

#include <vcsn/algos/copy.hh>
#include <vcsn/algos/transpose.hh>
#include <vcsn/core/join-automata.hh>
#include <vcsn/core/mutable-automaton.hh>
#include <vcsn/core/rat/visitor.hh>
#include <vcsn/ctx/fwd.hh>
#include <vcsn/ctx/traits.hh>
#include <vcsn/dyn/automaton.hh>
#include <vcsn/dyn/value.hh>
#include <vcsn/misc/memory.hh>
#include <vcsn/misc/raise.hh>
#include <vcsn/misc/tuple.hh>
#include <vcsn/misc/vector.hh> // make_vector

namespace vcsn
{
  /*-------------------------.
  | is_standard(automaton).  |
  `-------------------------*/

  template <Automaton Aut>
  bool
  is_standard(const Aut& a)
  {
    auto inis = initial_transitions(a);
    return
      inis.size() == 1
      && a->weightset()->is_one(a->weight_of(inis.front()))
      // No arrival on the initial state.
      && in(a, a->dst_of(inis.front())).empty();
  }

  template <Automaton Aut>
  bool
  is_costandard(const Aut& a)
  {
    return is_standard(transpose(a));
  }


  namespace dyn
  {
    namespace detail
    {
      template <Automaton Aut>
      bool
      is_standard(const automaton& aut)
      {
        const auto& a = aut->as<Aut>();
        return is_standard(a);
      }

      template <Automaton Aut>
      bool
      is_costandard(const automaton& aut)
      {
        const auto& a = aut->as<Aut>();
        return is_costandard(a);
      }
    }
  }

  /*----------------------.
  | standard(automaton).  |
  `----------------------*/

  template <Automaton Aut>
  void
  standard_here(Aut& aut)
  {
    if (is_standard(aut))
      return;

    const auto& ws = *aut->weightset();
    const auto& inits = initial_transitions(aut);
    std::vector<transition_t_of<Aut>> initials{begin(inits), end(inits)};

    // See Tools documentation for the implementation details.
    //
    // (i.a) Add a new state s...
    auto ini = aut->new_state();
    for (auto ti: initials)
      {
        // The initial state.
        auto i = aut->dst_of(ti);
        auto wi = aut->weight_of(ti);
        for (auto t: all_out(aut, i))
          // Cannot use new_transition.
          aut->add_transition(ini, aut->dst_of(t), aut->label_of(t),
                              ws.mul(wi, aut->weight_of(t)));
        aut->del_transition(ti);

        // (iv) Remove the former initial states of A that are the
        // destination of no incoming transition.
        if (all_in(aut, i).empty())
          aut->del_state(i);
      }
    // (i.b) Make [state s] initial, with initial multiplicity equal
    // to the unit of the multiplicity semiring.
    aut->set_initial(ini);
  }

  template <Automaton Aut>
  auto
  standard(const Aut& aut)
  {
    auto res = copy(aut);
    standard_here(res);
    return res;
  }

  template <Automaton Aut>
  auto
  costandard(const Aut& aut)
    -> decltype(copy(aut))
  {
    return transpose(standard(transpose(aut)));
  }


  namespace dyn
  {
    namespace detail
    {
      template <Automaton Aut>
      automaton
      standard(const automaton& aut)
      {
        const auto& a = aut->as<Aut>();
        return ::vcsn::standard(a);
      }

      template <Automaton Aut>
      automaton
      costandard(const automaton& aut)
      {
        const auto& a = aut->as<Aut>();
        return costandard(a);
      }
    }
  }


  /*------------------------.
  | standard(expression).   |
  `------------------------*/

  namespace rat
  {
    template <Automaton Aut,
              typename ExpSet>
    class standard_visitor
      : public ExpSet::const_visitor
    {
    public:
      using automaton_t = Aut;
      using expressionset_t = ExpSet;
      using expression_t = typename expressionset_t::value_t;
      using weightset_t = weightset_t_of<expressionset_t>;
      using weight_t = weight_t_of<expressionset_t>;
      using state_t = state_t_of<automaton_t>;

      using super_t = typename expressionset_t::const_visitor;

      constexpr static const char* me() { return "standard"; }

      standard_visitor(const expressionset_t& rs)
        : rs_(rs)
        , res_(make_shared_ptr<automaton_t>(rs_.context()))
      {}

      automaton_t operator()(const expression_t& v)
      {
        try
          {
            v->accept(*this);
            res_->set_initial(initial_);
            return std::move(res_);
          }
        catch (const std::runtime_error& e)
          {
            raise(e,
                  "  while computing standard automaton of: ",
                  to_string(rs_, v));
          }
      }

    private:
      VCSN_RAT_UNSUPPORTED(complement)
      VCSN_RAT_UNSUPPORTED(compose)
      VCSN_RAT_UNSUPPORTED(conjunction)
      VCSN_RAT_UNSUPPORTED(infiltrate)
      VCSN_RAT_UNSUPPORTED(ldivide)
      VCSN_RAT_UNSUPPORTED(shuffle)
      VCSN_RAT_UNSUPPORTED(transposition)
      using tuple_t = typename super_t::tuple_t;
      void visit(const tuple_t&, std::true_type) override
      {
        raise(me(), ": tuple is not supported");
      }

      VCSN_RAT_VISIT(zero,)
      {
        initial_ = res_->new_state();
      }

      VCSN_RAT_VISIT(one,)
      {
        auto i = res_->new_state();
        initial_ = i;
        res_->set_final(i);
      }

      VCSN_RAT_VISIT(atom, e)
      {
        auto i = res_->new_state();
        auto f = res_->new_state();
        initial_ = i;
        res_->new_transition(i, f, e.value());
        res_->set_final(f);
      }

      using states_t = std::set<state_t>;
      states_t finals() const
      {
        states_t res;
        for (auto t: final_transitions(res_))
          res.insert(res_->src_of(t));
        return res;
      }

      VCSN_RAT_VISIT(add, e)
      {
        states_t other_finals = finals();
        e.head()->accept(*this);
        state_t initial = initial_;
        for (const auto& c: e.tail())
          {
            c->accept(*this);
            for (auto t: all_out(res_, initial_))
              // Not set_transition: for instance 'a*+a*' will make
              // "initial" go twice to post().
              res_->add_transition(initial,
                                  res_->dst_of(t),
                                  res_->label_of(t),
                                  res_->weight_of(t));
            res_->del_state(initial_);
          }
        initial_ = initial;
      }

      VCSN_RAT_VISIT(mul, e)
      {
        // The set of the final states that were introduced in pending
        // parts of the automaton (for instance if we are in the rhs
        // of "a+bc", recording the final state for "a").
        states_t other_finals = finals();

        // Traverse the first part of the product, handle left_weight.
        e.head()->accept(*this);
        state_t initial = initial_;

        // Then the remainder.
        for (const auto& c: e.tail())
          {
            // The set of the current (left-hand side) final transitions.
            auto ftr = detail::make_vector(final_transitions(res_));

            // Visit the next member of the product.
            c->accept(*this);

            // Branch all the previously added final transitions to
            // the successors of the new initial state.
            for (auto t1: ftr)
              if (!has(other_finals, res_->src_of(t1)))
                {
                  // Remove the previous final transition first, as we
                  // might add a final transition for the same state
                  // later.
                  //
                  // For instance on "<2>a+(<3>\e+<5>a)", the final
                  // state s1 of <2>a will be made final thanks to
                  // <3>\e.  So if we compute the new transitions from
                  // s1 and then remove t1, we will have removed the
                  // fact that s1 is final thanks to <3>\e.
                  //
                  // Besides, s1 will become final with weight <3>, which
                  // might interfere with <5>a too.
                  auto s1 = res_->src_of(t1);
                  auto w1 = res_->weight_of(t1);
                  res_->del_transition(t1);
                  for (auto t2: all_out(res_, initial_))
                    res_->set_transition(s1,
                                        res_->dst_of(t2),
                                        res_->label_of(t2),
                                        ws_.mul(w1, res_->weight_of(t2)));
                }
            res_->del_state(initial_);
          }
        initial_ = initial;
      }

      // See star_here().
      VCSN_RAT_VISIT(star, e)
      {
        states_t other_finals = finals();
        e.sub()->accept(*this);
        // The "final weight of the initial state", starred.
        weight_t w = ws_.star(res_->get_final_weight(initial_));
        // Branch all the final states (but initial) to the successors
        // of initial.
        for (auto ti: out(res_, initial_))
          {
            res_->lweight(ti, w);
            for (auto tf: final_transitions(res_))
              if (res_->src_of(tf) != initial_
                  && !has(other_finals, res_->src_of(tf)))
                // Note that the weight of ti has already been
                // multiplied, on the left, by w.
                //
                // Not set_transition, as for instance with "a**", the
                // second star modifies many existing transitions.
                res_->add_transition
                  (res_->src_of(tf),
                   res_->dst_of(ti),
                   res_->label_of(ti),
                   ws_.mul(res_->weight_of(tf), res_->weight_of(ti)));
          }
        for (auto tf: final_transitions(res_))
          res_->rweight(tf, w);
        res_->set_final(initial_, w);
      }

      VCSN_RAT_VISIT(lweight, e)
      {
        e.sub()->accept(*this);
        for (auto t: all_out(res_, initial_))
          res_->lweight(t, e.weight());
      }

      VCSN_RAT_VISIT(rweight, e)
      {
        states_t other_finals = finals();
        e.sub()->accept(*this);
        for (auto t: final_transitions(res_))
          if (! has(other_finals, res_->src_of(t)))
            res_->rweight(t, e.weight());
      }

    private:
      const expressionset_t& rs_;
      const weightset_t& ws_ = *rs_.weightset();
      automaton_t res_;
      state_t initial_ = automaton_t::element_type::null_state();
    };

  } // rat::


  template <Automaton Aut,
            typename ExpSet>
  Aut
  standard(const ExpSet& rs, const typename ExpSet::value_t& r)
  {
    auto std = rat::standard_visitor<Aut, ExpSet>{rs};
    return std(r);
  }

  namespace dyn
  {
    namespace detail
    {
      template <typename ExpSet>
      automaton
      standard_expression(const expression& exp)
      {
        // FIXME: So far, there is a single implementation of expressions,
        // but we should actually be parameterized by its type too.
        using expressionset_t = ExpSet;
        using automaton_t
          = vcsn::mutable_automaton<context_t_of<expressionset_t>>;
        const auto& e = exp->as<expressionset_t>();
        return ::vcsn::standard<automaton_t>(e.valueset(), e.value());
      }
    }
  }

} // vcsn::