// etabench
// Copyright (C) 2022 xaizek <xaizek@posteo.net>
//
// This file is part of etabench.
//
// etabench is free software: you can redistribute it and/or modify
// it under the terms of version 3 of the GNU General Public License
// as published by the Free Software Foundation.
//
// etabench 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.
//
// You should have received a copy of the GNU General Public License
// along with etabench.  If not, see <https://www.gnu.org/licenses/>.

#ifndef ETABENCH__UTILS__PREDICATE_HPP__
#define ETABENCH__UTILS__PREDICATE_HPP__

namespace guts {

template <typename T>
struct Predicate;

template <typename C, typename T>
struct Predicate<T C::*>
{
    Predicate(T C::*p) : p(p)
    { }

    bool
    operator()(const C &a, const C &b) const
    { return a.*p < b.*p; }

    bool
    operator()(const C *a, const C *b) const
    { return operator()(*a, *b); }

    T C::*p;
};

template <typename C, typename R, typename... Args>
struct Predicate<R (C::*)(Args...) const>
{
    Predicate(R (C::*p)(Args...) const) : p(p)
    { }

    bool
    operator()(const C &a, const C &b) const
    { return (a.*p)() < (b.*p)(); }

    bool
    operator()(const C *a, const C *b) const
    { return operator()(*a, *b); }

    R (C::*p)(Args...) const;
};

template <typename P>
struct RPredicate
{
    RPredicate(P p) : p(p)
    { }

    template <typename T>
    bool
    operator()(const T &a, const T &b) const
    { return p(b, a); }

    P p;
};

}

// Usage example with a field:
//     std::sort(..., ..., makePredicate(&Entry::original));
//
// Usage example with a member function:
//     makePredicate(&Collection::getName));
template <typename T>
guts::Predicate<T>
makePredicate(T p)
{ return guts::Predicate<T>(p); }

// Same as makePredicate(), but in descending order.
template <typename T>
guts::RPredicate<guts::Predicate<T>>
makeRPredicate(T p)
{ return guts::RPredicate(guts::Predicate<T>(p)); }

#endif // ETABENCH__UTILS__PREDICATE_HPP__