/*
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 "library/unifier.h"
#include "library/tactic/elaborate.h"

namespace lean {
optional<expr> elaborate_with_respect_to(environment const & env, io_state const & ios, elaborate_fn const & elab,
                                         proof_state & s, expr const & e) {
    name_generator ngen = s.get_ngen();
    substitution subst  = s.get_subst();
    goals const & gs    = s.get_goals();
    if (empty(gs))
        return none_expr();
    auto ecs = elab(head(gs), ngen.mk_child(), e);
    expr new_e = ecs.first;
    buffer<constraint> cs;
    to_buffer(ecs.second, cs);
    if (cs.empty()) {
        // easy case: no constraints to be solved
        s = proof_state(s, ngen);
        return some_expr(new_e);
    } else {
        to_buffer(s.get_postponed(), cs);
        unifier_config cfg(ios.get_options());
        unify_result_seq rseq = unify(env, cs.size(), cs.data(), ngen.mk_child(), subst, cfg);
        if (auto p = rseq.pull()) {
            substitution new_subst     = p->first.first;
            constraints  new_postponed = p->first.second;
            new_e = new_subst.instantiate(new_e);
            s = proof_state(gs, new_subst, ngen, new_postponed);
            return some_expr(new_e);
        } else {
            return none_expr();
        }
    }
}
}