/*
Copyright (c) 2014 Microsoft Corporation. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.

Author: Leonardo de Moura
*/
#include "kernel/type_checker.h"
#include "library/reducible.h"
#include "library/tactic/tactic.h"
#include "library/tactic/elaborate.h"
#include "library/tactic/expr_to_tactic.h"

namespace lean {
tactic exact_tactic(elaborate_fn const & elab, expr const & e) {
    return tactic01([=](environment const & env, io_state const & ios, proof_state const & s) {
            proof_state new_s = s;
            if (auto new_e = elaborate_with_respect_to(env, ios, elab, new_s, e)) {
                name_generator ngen = new_s.get_ngen();
                substitution subst  = new_s.get_subst();
                goals const & gs    = new_s.get_goals();
                goal const & g      = head(gs);
                auto tc     = mk_type_checker(env, ngen.mk_child());
                auto e_t_cs = tc->infer(*new_e);
                expr t      = subst.instantiate(g.get_type());
                auto dcs    = tc->is_def_eq(e_t_cs.first, t);
                if (dcs.first && !dcs.second && !e_t_cs.second) {
                    expr new_p = g.abstract(*new_e);
                    check_has_no_local(new_p, e, "exact");
                    subst.assign(g.get_name(), new_p);
                    return some(proof_state(new_s, tail(gs), subst, ngen));
                }
            }
            return none_proof_state();
        });
}

static expr * g_exact_tac_fn      = nullptr;
expr const & get_exact_tac_fn() { return *g_exact_tac_fn; }
void initialize_exact_tactic() {
    name exact_tac_name({"tactic", "exact"});
    g_exact_tac_fn      = new expr(Const(exact_tac_name));
    register_tac(exact_tac_name,
                 [](type_checker &, elaborate_fn const & fn, expr const & e, pos_info_provider const *) {
                     check_tactic_expr(app_arg(e), "invalid 'exact' tactic, invalid argument");
                     return exact_tactic(fn, get_tactic_expr_expr(app_arg(e)));
                 });
}
void finalize_exact_tactic() {
    delete g_exact_tac_fn;
}
}