prelude.h

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/**********************************************************************
 * LeechCraft - modular cross-platform feature rich internet client.
 * Copyright (C) 2006-2014  Georg Rudoy
 *
 * Distributed under the Boost Software License, Version 1.0.
 * (See accompanying file LICENSE or copy at https://www.boost.org/LICENSE_1_0.txt)
 **********************************************************************/
 
#pragma once
 
#include <functional>
#include <type_traits>
#include <iterator>
#include <QPair>
#include <QStringList>
 
namespace boost
{
    template<typename>
    class iterator_range;
}
 
namespace LC
{
namespace Util
{
    template<typename T>
    struct WrapType
    {
        using type = T;
    };
 
    template<typename T>
    using WrapType_t = typename WrapType<T>::type;
 
    template<>
    struct WrapType<QList<QString>>
    {
        using type = QStringList;
    };
 
    template<template<typename U> class Container, typename T1, typename T2, typename F>
    auto ZipWith (const Container<T1>& c1, const Container<T2>& c2, F f) -> WrapType_t<Container<std::decay_t<std::result_of_t<F (T1, T2)>>>>
    {
        WrapType_t<Container<std::decay_t<std::result_of_t<F (T1, T2)>>>> result;
 
        using std::begin;
        using std::end;
 
        auto i1 = begin (c1), e1 = end (c1);
        auto i2 = begin (c2), e2 = end (c2);
        for ( ; i1 != e1 && i2 != e2; ++i1, ++i2)
            result.push_back (f (*i1, *i2));
        return result;
    }
 
    template<typename T1, typename T2,
        template<typename U> class Container,
        template<typename U1, typename U2> class Pair = QPair>
    auto Zip (const Container<T1>& c1, const Container<T2>& c2) -> Container<Pair<T1, T2>>
    {
        return ZipWith (c1, c2,
                [] (const T1& t1, const T2& t2) -> Pair<T1, T2>
                    { return { t1, t2}; });
    }
 
    namespace detail
    {
        template<typename Res, typename T>
        void Append (Res& result, T&& val) noexcept
        {
            if constexpr (requires { result.push_back (std::forward<T> (val)); })
                result.push_back (std::forward<T> (val));
            else
                result.insert (std::forward<T> (val));
        }
 
        template<typename>
        struct CountArgs
        {
            static const size_t ArgsCount = 0;
        };
 
        template<template<typename...> class Container, typename... Args>
        struct CountArgs<Container<Args...>>
        {
            static const size_t ArgsCount = sizeof... (Args);
        };
 
        template<typename C>
        constexpr bool IsSimpleContainer ()
        {
            return CountArgs<std::decay_t<C>>::ArgsCount == 1;
        }
 
        template<typename Container, typename T>
        struct Replace
        {
            using Type = struct Fail;
        };
 
        template<template<typename> class Container, typename U, typename T>
        struct Replace<Container<U>, T>
        {
            using Type = Container<T>;
        };
 
        template<typename>
        struct IsNotBrokenSFINAE : std::false_type {};
 
        template<typename T>
        struct IsNotBrokenSFINAE<boost::iterator_range<T>> : std::true_type {};
 
        template<typename T>
        constexpr bool IsNotBrokenSFINAE_v = IsNotBrokenSFINAE<T> {};
 
        template<template<typename...> class Fallback, bool ForceFallback, typename Container, typename F>
        auto MapImpl (Container&& c, F f)
        {
            using FRet_t = std::decay_t<decltype (std::invoke (f, *c.begin ()))>;
            static_assert (!std::is_same<void, FRet_t> {}, "The function shall not return void.");
 
            using DecayContainer_t = std::decay_t<Container>;
 
            using ResultCont_t = std::conditional_t<
                    !ForceFallback &&
                        detail::IsSimpleContainer<DecayContainer_t> () &&
                        !detail::IsNotBrokenSFINAE_v<DecayContainer_t>,
                    typename detail::Replace<DecayContainer_t, FRet_t>::Type,
                    Fallback<FRet_t>>;
 
            WrapType_t<ResultCont_t> cont;
            for (auto&& t : c)
                Append (cont, std::invoke (f, t));
            return cont;
        }
    }
 
    // NOTE
    // The noexcept specifier here is somewhat misleading:
    // this function indeed _might_ throw if the underlying container throws
    // when appending an element, for any reason,
    // (be it a copy/move ctor throwing or failure to allocate memory).
    // Due to how LC is written and intended to be used,
    // such exceptions are not and should not be handled,
    // so they are fatal anyway.
    // Thus we're totally fine with std::unexpected() and the likes.
    template<typename Container, typename F>
    auto Map (Container&& c, F&& f) noexcept (noexcept (std::is_nothrow_invocable_v<F, decltype (*c.begin ())>))
    {
        return detail::MapImpl<QList, false> (std::forward<Container> (c), std::forward<F> (f));
    }
 
    template<template<typename...> class Fallback, typename Container, typename F>
    auto MapAs (Container&& c, F&& f) noexcept (noexcept (std::is_nothrow_invocable_v<F, decltype (*c.begin ())>))
    {
        return detail::MapImpl<Fallback, true> (std::forward<Container> (c), std::forward<F> (f));
    }
 
    template<typename T, template<typename U> class Container, typename F>
    Container<T> Filter (const Container<T>& c, F f)
    {
        Container<T> result;
        for (const auto& item : c)
            if (std::invoke (f, item))
                detail::Append (result, item);
        return result;
    }
 
    template<template<typename> class Container, typename T>
    Container<T> Concat (const Container<Container<T>>& containers)
    {
        Container<T> result;
        for (const auto& cont : containers)
            std::copy (cont.begin (), cont.end (), std::back_inserter (result));
        return result;
    }
 
    template<template<typename...> class Container, typename... ContArgs>
    auto Concat (const Container<ContArgs...>& containers) -> std::decay_t<decltype (*containers.begin ())>
    {
        std::decay_t<decltype (*containers.begin ())> result;
        for (const auto& cont : containers)
            for (const auto& item : cont)
                detail::Append (result, item);
        return result;
    }
 
    template<typename Cont, typename F>
    auto ConcatMap (Cont&& c, F&& f)
    {
        return Concat (Map (std::forward<Cont> (c), std::forward<F> (f)));
    }
 
    template<template<typename> class Container, typename T>
    Container<Container<T>> SplitInto (size_t numChunks, const Container<T>& container)
    {
        Container<Container<T>> result;
 
        const size_t chunkSize = container.size () / numChunks;
        for (size_t i = 0; i < numChunks; ++i)
        {
            Container<T> subcont;
            const auto start = container.begin () + chunkSize * i;
            const auto end = start + chunkSize;
            std::copy (start, end, std::back_inserter (subcont));
            result.push_back (subcont);
        }
 
        const auto lastStart = container.begin () + chunkSize * numChunks;
        const auto lastEnd = container.end ();
        std::copy (lastStart, lastEnd, std::back_inserter (result.front ()));
 
        return result;
    }
 
    template<typename Cont>
    decltype (auto) Sorted (Cont&& cont)
    {
        std::sort (cont.begin (), cont.end ());
        return std::forward<Cont> (cont);
    }
 
    constexpr auto Id = [] (auto&& t) -> decltype (auto) { return std::forward<decltype (t)> (t); };
 
    template<typename R>
    auto ComparingBy (R r)
    {
        return [r] (const auto& left, const auto& right) { return std::invoke (r, left) < std::invoke (r, right); };
    }
 
    template<typename R>
    auto EqualityBy (R r)
    {
        return [r] (const auto& left, const auto& right) { return std::invoke (r, left) == std::invoke (r, right); };
    }
 
    constexpr auto Apply = [] (const auto& t) { return t (); };
 
    constexpr auto Fst = [] (const auto& pair) { return pair.first; };
 
    constexpr auto Snd = [] (const auto& pair) { return pair.second; };
 
    template<typename F>
    auto First (F&& f)
    {
        return [f = std::forward<F> (f)] (const auto& pair) { return std::invoke (f, pair.first); };
    }
 
    template<typename F>
    auto Second (F&& f)
    {
        return [f = std::forward<F> (f)] (const auto& pair) { return std::invoke (f, pair.second); };
    }
}
}