libcruft-util/iterator/transform.hpp

/*
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 *
 * Copyright 2010-2018 Danny Robson <danny@nerdcruft.net>
 */

#pragma once

#include "../view.hpp"

#include <algorithm>
#include <utility>


namespace cruft::iterator {
    ///////////////////////////////////////////////////////////////////////////
    template <typename OutputIt, typename FunctionT>
    OutputIt
    _transform_by_block (
        const cruft::view<OutputIt> &,
        OutputIt cursor,
        FunctionT &&
    ) {
        return cursor;
    }


    //-------------------------------------------------------------------------
    template <typename OutputIt, typename FunctionT, typename InputT, typename ...TailT>
    OutputIt
    _transform_by_block (
        const cruft::view<OutputIt> &dst,
        OutputIt cursor,
        FunctionT &&func,
        const InputT &_src,
        TailT &&...tail
    ) {
        auto remain = _src;
        if (cursor != dst.begin ()) {
            auto infill = std::distance (cursor, dst.end ());
            if (remain.size () < static_cast<size_t> (infill)) {
                return _transform_by_block (
                    dst,
                    std::copy_n (remain.begin (), remain.size (), cursor),
                    std::forward<FunctionT> (func),
                    std::forward<TailT> (tail)...
                );
            }

            std::copy_n (remain.begin (), infill, cursor);
            func (dst);
            cursor = dst.begin ();
            remain = { remain.begin () + infill, remain.end () };
        }

        while (remain.size () >= dst.size ()) {
            std::copy_n (remain.begin (), dst.size (), dst.begin ());
            func (dst);
            remain = { remain.begin () + dst.size (), remain.end () };
        }

        return _transform_by_block (
            dst,
            std::copy (remain.begin (), remain.end (), cursor),
            std::forward<FunctionT> (func),
            std::forward<TailT> (tail)...
        );
    }


    //-------------------------------------------------------------------------
    template <typename OutputIt, typename FunctionT, typename ...Args>
    OutputIt
    transform_by_block (const cruft::view<OutputIt> &dst, FunctionT &&func, Args &&...src)
    {
        return _transform_by_block (
            dst,
            dst.begin (),
            std::forward<FunctionT> (func),
            std::forward<Args> (src)...
        );
    }
};