/*
Copyright (c) 2013 Microsoft Corporation. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.

Author: Leonardo de Moura
*/
#pragma once
#include <algorithm>
#include <utility>
#include <memory>
#include <mutex>
#include "util/lazy_list.h"
#include "library/io_state.h"
#include "library/tactic/proof_state.h"

namespace lean {
typedef lazy_list<proof_state> proof_state_seq;

class tactic_cell {
    void dealloc() { delete this; }
    MK_LEAN_RC();
public:
    tactic_cell():m_rc(0) {}
    virtual ~tactic_cell() {}
    virtual proof_state_seq operator()(environment const & env, io_state const & io, proof_state const & s) = 0;
};

class tactic {
protected:
    tactic_cell * m_ptr;
public:
    explicit tactic(tactic_cell * ptr):m_ptr(ptr) { if (m_ptr) m_ptr->inc_ref(); }
    tactic(tactic const & s):m_ptr(s.m_ptr) { if (m_ptr) m_ptr->inc_ref(); }
    tactic(tactic && s):m_ptr(s.m_ptr) { s.m_ptr = nullptr; }
    ~tactic() { if (m_ptr) m_ptr->dec_ref(); }
    friend void swap(tactic & a, tactic & b) { std::swap(a.m_ptr, b.m_ptr); }
    tactic & operator=(tactic const & s);
    tactic & operator=(tactic && s);

    proof_state_seq operator()(environment const & env, io_state const & io, proof_state const & s) { return m_ptr->operator()(env, io, s); }

    expr solve(environment const & env, io_state const & io, proof_state const & s);
    expr solve(environment const & env, io_state const & io, context const & ctx, expr const & t);
};

template<typename F>
class simple_tactic_cell : public tactic_cell {
    F m_f;
public:
    simple_tactic_cell(F && f):m_f(f) {}
    virtual proof_state_seq operator()(environment const & env, io_state const & io, proof_state const & s) {
        return m_f(env, io, s);
    }
};

/**
   \brief Create a tactic using the given functor.
   The functor must contain the operator:

   <code>
   proof_state_seq operator()(environment const & env, io_state const & io, proof_state const & s)
   </code>
*/
template<typename F>
tactic mk_tactic(F && f) { return tactic(new simple_tactic_cell<F>(std::forward<F>(f))); }

/**
   \brief Return a "do nothing" tactic (aka skip).
*/
tactic id_tactic();
/**
   \brief Return a tactic the always fails.
*/
tactic fail_tactic();
/**
   \brief Return a tactic that fails if there are unsolved goals.
*/
tactic now_tactic();
/**
   \brief Return a tactic that solves any goal of the form  <tt>..., H : A, ... |- A</tt>.
*/
tactic assumption_tactic();
/**
   \brief Return a tactic that performs \c t1 followed by \c t2.
*/
tactic then(tactic t1, tactic t2);
/**
   \brief Return a tactic that applies \c t1, and if \c t1 returns the empty sequence of states,
   then applies \c t2.
*/
tactic orelse(tactic t1, tactic t2);
/**
   \brief Return a tactic that tries the tactic \c t for at most \c ms milliseconds.
   If the tactic does not terminate in \c ms milliseconds, then the empty
   sequence is returned.

   \remark the tactic \c t is executed in a separate execution thread.

   \remark \c check_ms is how often the main thread checks whether the child
   thread finished.
*/
tactic try_for(tactic t, unsigned ms, unsigned check_ms = 1);
/**
   \brief Execute both tactics and and combines their results.
   The results produced by tactic \c t1 are listed before the ones
   from tactic \c t2.
*/
tactic append(tactic t1, tactic t2);
/**
   \brief Execute both tactics and and combines their results.
   The results produced by tactics \c t1 and \c t2 are interleaved
   to guarantee fairness.
*/
tactic interleave(tactic t1, tactic t2);
/**
   \brief Return a tactic that executs \c t1 and \c t2 in parallel.
   It returns the sequence produced by the first to terminate.

   \remark \c check_ms is how often the main thread checks whether the children
   threads finished.
*/
tactic par(tactic t1, tactic t2, unsigned check_ms = 1);
/**
   \brief Return a tactic that keeps applying \c t until it fails.
*/
tactic repeat(tactic t);
/**
   \brief Similar to \c repeat, but execute \c t at most \c k times.

   \remark The value \c k is the depth of the recursion.
   For example, if tactic \c t always produce a sequence of size 2,
   then tactic \c t will be applied 2^k times.
*/
tactic repeat_at_most(tactic t, unsigned k);
}