PDF4QT/PdfForQtLib/sources/pdfflatarray.h

//    Copyright (C) 2019 Jakub Melka
//
//    This file is part of PdfForQt.
//
//    PdfForQt is free software: you can redistribute it and/or modify
//    it under the terms of the GNU Lesser General Public License as published by
//    the Free Software Foundation, either version 3 of the License, or
//    (at your option) any later version.
//
//    PdfForQt 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 Lesser General Public License for more details.
//
//    You should have received a copy of the GNU Lesser General Public License
//    along with PDFForQt.  If not, see <https://www.gnu.org/licenses/>.


#ifndef PDFFLATARRAY_H
#define PDFFLATARRAY_H

#include <QtGlobal>

#include <array>
#include <vector>
#include <algorithm>

namespace pdf
{

/// This represents a fast array, consisting of "fast" block of fixed size \p FlatSize,
/// and "slow" block of variable size. Usually, this array is used when vast majority
/// of usage size is below FlatSize, only minority is above FlatSize. Typical example
/// of use of this class:
///
/// We have colors in PDF, which can have usually 1, 3 or 4 color components. But in some
/// rare cases, we have much more components, for example for DeviceN color spaces.
/// For this reason, we will set FlatSize to 4 (so Gray, RGB and CMYK colors will not
/// use slow "variable" part).
template<typename T, size_t FlatSize>
class PDFFlatArray
{
public:
    explicit PDFFlatArray() :
        m_flatBlock(),
        m_flatBlockEndIterator(m_flatBlock.begin()),
        m_variableBlock()
    {

    }

    template<typename... Arguments, typename std::enable_if<sizeof...(Arguments) < FlatSize, int>::type = 0>
    explicit inline PDFFlatArray(Arguments... arguments) :
        m_flatBlock(arguments...),
        m_flatBlockEndIterator(std::next(m_flatBlock.begin(), sizeof...(Arguments))),
        m_variableBlock()
    {

    }

    /// Returns the size of the array
    size_t size() const { return getFlatBlockSize() + m_variableBlock.size(); }

    /// Returns true, if array is empty
    bool empty() const { return size() == 0; }

    template<size_t index>
    const T& get() const
    {
        if constexpr (index < FlatSize)
        {
            return m_flatBlock[size];
        }
        else
        {
            return m_variableBlock[size - FlatSize];
        }
    }

    template<size_t index>
    T& get()
    {
        if constexpr (index < FlatSize)
        {
            return m_flatBlock[size];
        }
        else
        {
            return m_variableBlock[size - FlatSize];
        }
    }

    const T& operator[] (size_t index) const
    {
        Q_ASSERT(index < size());

        if (index < FlatSize)
        {
            return m_flatBlock[index];
        }
        else
        {
            return m_variableBlock[index - FlatSize];
        }
    }

    void clear()
    {
        m_flatBlockEndIterator = m_flatBlock.begin();
        m_variableBlock.clear();
    }

    void push_back(T object)
    {
        if (m_flatBlockEndIterator != m_flatBlock.cend())
        {
            *m_flatBlockEndIterator++ = std::move(object);
        }
        else
        {
            m_variableBlock.emplace_back(std::move(object));
        }
    }

private:
    size_t getFlatBlockSize() const { return std::distance(m_flatBlock.cbegin(), std::array<T, FlatSize>::const_iterator(m_flatBlockEndIterator)); }

    std::array<T, FlatSize> m_flatBlock;
    typename std::array<T, FlatSize>::iterator m_flatBlockEndIterator; ///< Pointer to the end of flat block
    std::vector<T> m_variableBlock;
};

}   // namespace pdf

#endif // PDFFLATARRAY_H