/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4; fill-column: 100 -*- */
/*
 * This file is part of the LibreOffice project.
 *
 * 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/.
 */

#ifndef INCLUDED_O3TL_SPAN_HXX
#define INCLUDED_O3TL_SPAN_HXX

#include <sal/config.h>

#include <config_global.h>

#if HAVE_CPP_SPAN

#include <span>

namespace o3tl { using std::span; }

#else

#include <cassert>
#include <cstddef>
#include <iterator>
#include <type_traits>
#include <vector>

namespace o3tl {

/** A barebones approximation of C++20 <span>.
*/
template<typename T>
class span {
public:
    using value_type = T;
    using pointer = value_type *;
    using const_pointer = value_type const *;
    using reference = value_type &;
    using const_reference = value_type const &;
    using const_iterator = const_pointer;
    using iterator = pointer;
    using const_reverse_iterator = std::reverse_iterator<const_iterator>;
    using reverse_iterator = std::reverse_iterator<iterator>;
    using size_type = std::size_t;
    using difference_type = std::ptrdiff_t;

    constexpr span() noexcept : data_(nullptr), size_(0) {}

    template<std::size_t N>
    constexpr span (T (&a)[N]) noexcept : data_(a), size_(N) {}

    constexpr span (T *a, size_type len) noexcept
        : data_(a), size_(len)
    {
        // not terribly sure about this, might need to strengthen it
        assert(a != nullptr || len == 0);
    }

    template<typename T2>
    constexpr span(const std::vector<T2>& vec)
        : data_(vec.data()), size_(vec.size()) {}

    /** for assigning from span<T> to span<const T> */
    constexpr span (const span<typename std::remove_const<T>::type>& other) noexcept
        : data_(other.data()), size_(other.size()) {}

    constexpr bool empty() const noexcept { return size_ == 0; }

    constexpr iterator begin() const noexcept { return data_; }
    constexpr iterator end() const noexcept { return begin() + size(); }

    reverse_iterator rbegin() const noexcept
    { return reverse_iterator(end()); }
    reverse_iterator rend() const noexcept
    { return reverse_iterator(begin()); }

    constexpr size_type size() const noexcept { return size_; }

    constexpr reference operator [](size_type pos) const {
        assert(pos < size());
        return data_[pos];
    }

    constexpr pointer data() const noexcept { return data_; }

private:
    pointer    data_;
    size_type size_;
};

} // namespace o3tl

#endif

#endif

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