#pragma once

#include <array>
#include <cassert>
#include <cstdint>
#include <string>
#include <vector>
#if __cpp_lib_ranges
#include <ranges>
#endif
#if __cpp_lib_string_view
#include <string_view>
#endif
#if __cpp_lib_span
#include <span>
#endif
#include <type_traits>

//! @file rust_types.hh
//! @brief This file contains matching C++ types for `ffi_types` crate.
//!
//! The types can be used for either bindgen, cbindgen or hand-crafted C/C++ code.
//! The types without C-prefixes are ownership-aware types compatible with Rust types.
//! The types with C-prefixes are C ABI compatible layout of its paired owned types.
//! C-prefixes types are very fragile! Please read the following warning to use it safe.
//!
//! @warning All types prefixed with `C` in this file are C ABI compatible layout of owned types without `C` prefix.
//!          To avoid memory leak, you must convert it to owned type or pass it to Rust side.
//!          You *MUST* run one of the following to avoid memory leak:
//!
//!          1. Calling operator() to convert to owned type.
//!             1.1 When used in bindgen generated functions' arguments.
//!             ```c++
//!             void foo(CBoxedSlice<uint32_t> ints) {
//!                 auto owned = ints();  // owned is managed as BoxedSlice<uint32_t>
//!             }
//!             ```
//!
//!             1.2 When used in cbindgen generated functions' return value.
//!             ```rust
//!             fn foo() -> CBoxedSlice<u32> { ... }
//!             ```
//!             ```c++
//!             auto owned = foo()();  // owned is managed as BoxedSlice<uint32_t>
//!             ```
//!
//!             1.3 Dropping in C++ side.
//!             The owned value in either 1.1 or 1.2 must be returned to Rust side or dropped.
//!             See 2.1 to return value.
//!             Implement template specialization for `_drop()` for the related type to drop it in C++ side.
//!             (e.g. BoxedSlice<uint32_t>::_drop() for BoxedSlice<uint32_t>)
//!             The _drop function must call `std::mem::drop()` from rust side.
//!
//!          2. Passing as an argument of Rust function.
//!             2.1 When used in cbindgen generated functions' arguments.
//!             ```rust
//!             fn foo() -> CBoxedSlice<u32> { ... }   // See 1.2 for this case
//!             fn bar(ints: CBoxedSlice<u32>) { ... }
//!             ```
//!             ```c++
//!             auto owned = foo()();  // owned is managed as BoxedSlice<uint32_t>
//!             bar(owned);  // BoxedSlice can be passed to CBoxedSlice
//!             ```
//!
//!          3. Returning from C++ function. Note that this case will be very unlikely to happen because Box must be
//!          created from Rust side.
//!
//! @note allocate or deallocate a boxed type in C++ side is not allowed.

namespace ffi_types {

/// Alias for Rust `std::usize`.
using usize = uintptr_t;

/// Alias for Rust `[T; N]`. Interpreted as std::array in C++ side.
template <typename T, usize N>
using Array = std::array<T, N>;

}  // namespace ffi_types

#if _MSC_VER
#define _COPY_DELETE default
#else
#define _COPY_DELETE delete
#endif
namespace ffi_types {

template <typename T>
struct CBox;

/// C++ counterpart for Rust `Option<Box<T>>` managed by C++ ownership model.
//
/// The API design is similar to `std::unique_ptr`, though construction and destruction
/// must be executed in Rust side.
///
/// @warning The underlying memory must be allocated from Rust side.
template <typename T>
struct OptionBox {
    using element_type = T;
    using pointer = T*;

    T* _ptr;

    // constructors
    OptionBox() = delete;
    OptionBox(OptionBox&) = delete;
    OptionBox(OptionBox&& b) noexcept : _ptr(b.release()) {}
    explicit OptionBox(std::nullptr_t) noexcept : _ptr(nullptr) {}

    explicit OptionBox(pointer p) noexcept : _ptr(p) {}

    // destructor and helper
    ~OptionBox() noexcept {
        if (this->get()) {
            this->_drop();
        }
    }
    void _drop() noexcept;

    // assignment
    OptionBox& operator=(OptionBox&& b) noexcept {
        this->_ptr = b.release();
        return *this;
    }

    /// Converts to `CBox<T>` by moving the value.
    /// The value of `this` will be invalidated to null.
    CBox<T> into() noexcept;

    /// Borrow as `CBox<T>`.
    /// This is safe because CBox is a reference.
    CBox<T>& as_c() noexcept {
        return *reinterpret_cast<CBox<T>*>(this);
    }

    /// Borrow as `CBox<T>`.
    /// This is safe because CBox is a reference.
    const CBox<T>& as_c() const noexcept {
        return *reinterpret_cast<const CBox<T>*>(this);
    }

    // observers
    typename std::add_lvalue_reference<element_type>::type operator*() const {
        return *get();
    }
    pointer operator->() const {
        return get();
    }
    pointer get() const {
        return this->_ptr;
    }
    explicit operator bool() const noexcept {
        return get() != nullptr;
    }

    // operators
    bool operator==(std::nullptr_t) const {
        return this->get() == nullptr;
    }
    bool operator!=(std::nullptr_t) const {
        return this->get() != nullptr;
    }

    // modifiers
    T* release() noexcept {
        auto* ptr = this->_ptr;
        this->_ptr = 0;
        return ptr;
    }
    void reset(pointer p) noexcept {
        if (this->get()) {
            this->_drop();
        }
        this->_ptr = p;
    }
};
static_assert(sizeof(OptionBox<int>) == sizeof(int*));
static_assert(std::is_standard_layout<OptionBox<int>>::value);

/// C++ counterpart for Rust `Box<T>` as alias of `OptionBox<T>`.
/// Since `Box<T>` can be moved or released, a value of this type is still not guaranteed to be non-null.
///
/// @warning The underlying memory must be allocated from Rust side.
template <typename T>
struct Box : public OptionBox<T> {
    explicit Box(T* p) noexcept : OptionBox<T>(p) {
        assert(p != nullptr);
    }
};

/// C++ wrapper for Rust `Box<T>` with C ABI compatible layout.
///
/// @warning This type does *NOT* implement a safe destructor.
///          To avoid leak, see general note about C-prefixed types at the top of module documentation.
template <typename T>
struct [[nodiscard]] CBox {
    CBox() = _COPY_DELETE;
    CBox(const CBox&) = _COPY_DELETE;
    CBox& operator=(const CBox& b) noexcept = _COPY_DELETE;

    T* _ptr;

#if _MSC_VER
    /// Creates a CBox from a `OptionBox<T>` by moving the value.
    /// This is a workaround for MSVC constructor limitation.
    static CBox from(OptionBox<T>&& box) noexcept {
        CBox cbox;
        cbox._ptr = box.release();
        return cbox;
    }
#else
    CBox(CBox&&) = default;
    CBox& operator=(CBox&& b) noexcept = default;
    CBox(OptionBox<T>&& box) noexcept : _ptr(box.release()) {}

    /// Creates a CBox from a `OptionBox<T>` by moving the value.
    /// This is a workaround for MSVC constructor limitation.
    static CBox from(OptionBox<T>&& box) noexcept {
        return CBox(std::move(box));
    }
#endif

    /// Conversion operator to check if the box is not null.
    explicit operator bool() const noexcept {
        return _ptr != nullptr;
    }

    /// Equality operator with nullptr.
    bool operator==(std::nullptr_t) noexcept {
        return _ptr == nullptr;
    }

    /// Conversion operator to `OptionBox<T>`.
    ///
    /// Though the creation of `CBox` is always expected to be non-null by Rust Side,
    /// `CBox` itself still can be a null due to move.
    ///
    /// @note This conversion *MUST* be called unless the value is going to be passed to Rust side.
    OptionBox<T> operator()() noexcept {
        auto box = OptionBox<T>(nullptr);
        box.reset(this->_ptr);
        this->_ptr = nullptr;
        return box;
    }

    T* release() noexcept {
        auto* ptr = this->_ptr;
        this->_ptr = nullptr;
        return ptr;
    }
};
static_assert(sizeof(CBox<int>) == sizeof(int*));
static_assert(std::is_trivial<CBox<int>>::value);
static_assert(std::is_standard_layout<CBox<int>>::value);

/// C++ wrapper for Rust `Option<Box<T>>` as alias of `CBox<T>`.
///
/// This is a cbindgen helper to pass `Option<Box<T>>` to C++ side.
///
/// @see CBox
template <typename T>
using COptionBox = CBox<T>;

template <typename T>
inline CBox<T> OptionBox<T>::into() noexcept {
    return CBox<T>::from(std::move(*this));
}

// specializations to prohibit void box drop
template struct CBox<void>;

template <>
inline void OptionBox<void>::_drop() noexcept {
    assert("void box doesn't support drop" && false);
}

}  // namespace ffi_types
namespace ffi_types {

#define EMPTY_SLICE_BEGIN(T) reinterpret_cast<T*>(1)

template<typename T>
T* _wrap_null(T* ptr) {
    return ptr ? ptr : reinterpret_cast<T*>(1);
}

// C++ std::ranges compatibility layer until C++17.
#if __cpp_lib_ranges
namespace ranges {
using std::ranges::data;
using std::ranges::size;
}  // namespace ranges
#define SAFE_R R&&
#else
namespace ranges {
template <typename C>
auto data(C& x) noexcept {
    auto begin = x.begin();

    using iterator_type = decltype(begin);
    using pointer_type = decltype(&*begin);

    if constexpr (std::is_same_v<iterator_type, pointer_type>) {
        // same type
        return begin;
    } else if constexpr (sizeof(iterator_type) == sizeof(uintptr_t)) {
        // likely to be a pointer
        return *reinterpret_cast<pointer_type*>(&begin);
    } else {
        if (begin != x.end()) {
            return &*begin;
        } else {
            return static_cast<pointer_type>(nullptr);
        }
    }
}

template <typename C>
size_t size(C& x) noexcept {
    return x.end() - x.begin();
}
}  // namespace ranges
// R&& is not safe without actual ranges
#define SAFE_R const R&
#endif

struct CharStrRef;
struct StrRef;
struct CStrRef;
struct CByteSliceRef;
class BoxedStr;

template <typename T>
struct CMutSliceRef;
template <typename T>
struct CSliceRef;
template <typename T>
struct CBoxedSlice;

/// A minimal range type of slices to be compatible with internal ranges.
template <typename T>
struct _SliceRange {
    T* _data;
    usize _size;

    auto* begin() const noexcept {
        return this->_data;
    }
    auto* end() const noexcept {
        return this->_data + _size;
    }
};

/// Common C++ STL-like interface for &[T] and &str.
/// @see std::span
template <typename T, template <typename _> typename I>
struct _SliceInterface {
    // constants and types
    using element_type = T;
    using value_type = typename std::remove_cv_t<T>;
    using size_type = uintptr_t;
    using difference_type = intptr_t;
    using pointer = element_type*;
    using const_pointer = const element_type*;
    using reference = element_type&;
    using const_reference = const element_type&;
#if __cpp_lib_span
    using iterator = typename std::span<element_type>::iterator;
#else
    using iterator = pointer;
#endif
    using reverse_iterator = std::reverse_iterator<iterator>;

    // observers
    size_type size() const noexcept {
        return static_cast<const I<T>*>(this)->_size;
    }
    size_type size_bytes() const noexcept {
        return this->size() * sizeof(element_type);
    }
    bool empty() const noexcept {
        return this->size() == 0;
    }

    // element access
    reference operator[](size_type idx) const noexcept {
        assert(idx < this->size());
        return this->data()[idx];
    }
    reference front() const noexcept {
        return this->data()[0];
    }
    reference back() const noexcept {
        return this->data()[size() - 1];
    }
    pointer data() const noexcept {
        return static_cast<const I<T>*>(this)->_data;
    }

    // iterator
#if __cpp_lib_span
    iterator begin() const noexcept {
        return span().begin();
    }
#else
    iterator begin() const noexcept {
        return data();
    }
#endif
    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());
    }

    _SliceRange<element_type> get() const noexcept {
        return {data(), size()};
    }

#if __cpp_lib_span
    /// Returns the slice as a `std::span`.
    std::span<element_type> span() const noexcept {
        return std::span<T>(data(), size());
    }
#endif
};

/// C++ counterpart of Rust `&mut [T]` and &[T]`.
/// The interface is following `std::span` design.
template <typename T>
struct MutSliceRef : public _SliceInterface<T, MutSliceRef> {
    T* _data;
    usize _size;

    MutSliceRef() noexcept : _data(EMPTY_SLICE_BEGIN(T)), _size(0) {}
    MutSliceRef(const MutSliceRef&) = default;
    MutSliceRef(MutSliceRef&&) = default;
    explicit MutSliceRef(T* head, usize size) noexcept : _data(_wrap_null(head)), _size(size) {}
    template <class R>
    MutSliceRef(SAFE_R range) noexcept : _data(_wrap_null(ranges::data(range))), _size(static_cast<usize>(ranges::size(range))) {}

    MutSliceRef& operator=(const MutSliceRef<T>&) = default;
    MutSliceRef& operator=(MutSliceRef<T>&&) = default;

    CMutSliceRef<T> into() const noexcept;

    /// Convert &[u8] to C++ string wrapper.
    /// This is &[u8] specialization as bytes
    template <typename U = T>
    std::enable_if_t<std::is_same_v<U, const uint8_t>, CharStrRef> as_char_str() const noexcept;

    /// Convert &[u8] to Rust string wrapper without UTF-8 checking.
    /// This is &[u8] specialization as bytes
    ///
    /// @warning Safety: Only when the data is a valid UTF-8 string.
    template <typename U = T>
    std::enable_if_t<std::is_same_v<U, const uint8_t>, StrRef> as_str_unchecked() const noexcept;
};
static_assert(std::is_trivially_copyable<MutSliceRef<usize>>::value);
static_assert(std::is_standard_layout<MutSliceRef<usize>>::value);

/// SliceRef<T> is a read-only slice `&[T]` in Rust and a conceptional alias to `MutSliceRef<const T>` in C++.
/// This is not a hard alias because:
/// - template alias doesn't support generic parameter deduction.
/// - bindgen resolve template alias to the original type, which we don't supposed to do.
template <typename T>
struct SliceRef : public MutSliceRef<const T> {
    SliceRef() noexcept : MutSliceRef<const T>(){};
    SliceRef(const SliceRef&) = default;
    SliceRef(SliceRef&&) = default;
    explicit SliceRef(const T* head, usize size) noexcept : MutSliceRef<const T>(head, size) {}
    template <class R>
    SliceRef(SAFE_R range) noexcept : MutSliceRef<const T>(range) {}

    SliceRef& operator=(const SliceRef<T>&) = default;
    SliceRef& operator=(SliceRef<T>&&) = default;

    typename std::conditional<std::is_same_v<T, uint8_t>, CByteSliceRef, CSliceRef<T>>::type into() const noexcept;

    template <typename B, typename U = T>
    static std::enable_if_t<std::is_same_v<U, uint8_t>, SliceRef<uint8_t>> from_buffer(const B& buffer) noexcept {
        return SliceRef<uint8_t>(reinterpret_cast<const uint8_t*>(&buffer), sizeof(B));
    }
};
static_assert(std::is_trivially_copyable<SliceRef<usize>>::value);
static_assert(std::is_standard_layout<SliceRef<usize>>::value);

/// C++ counterpart of `&[u8]` as alias for `SliceRef<uint8_t>`.
/// This alias is useful to pass `&[u8]` in cbindgen without configuration and boilerplate.
using ByteSliceRef = SliceRef<uint8_t>;

template <typename T>
struct CMutSliceRef {
    CMutSliceRef() = _COPY_DELETE;
    CMutSliceRef(const CMutSliceRef&) = default;
    CMutSliceRef& operator=(const CMutSliceRef<T>&) = default;

#if _MSC_VER
    /// Creates a `CMutSliceRef` from a `MutSliceRef`.
    /// This is a workaround for MSVC constructor limitation.
    static CMutSliceRef from(const MutSliceRef<T>& slice) noexcept {
        CMutSliceRef s;
        s._data = slice._data;
        s._size = slice._size;
        return s;
    }
#else
    CMutSliceRef(const MutSliceRef<T>& slice) noexcept {
        this->_data = slice._data;
        this->_size = slice._size;
    }
    /// Creates a `CMutSliceRef` from a `MutSliceRef`.
    /// This is a workaround for MSVC constructor limitation.
    static CMutSliceRef from(const MutSliceRef<T>& slice) noexcept {
        return CMutSliceRef(slice);
    }
#endif

    T* _data;
    usize _size;

    MutSliceRef<T> operator()() const noexcept {
        return MutSliceRef<T>(this->_data, this->_size);
    }
};
static_assert(std::is_trivial<CMutSliceRef<usize>>::value);
static_assert(std::is_standard_layout<CMutSliceRef<usize>>::value);

template <typename T>
struct CSliceRef {
    CSliceRef() = _COPY_DELETE;
    CSliceRef(const CSliceRef&) = default;
    CSliceRef& operator=(const CSliceRef<T>&) = default;

#if _MSC_VER
    /// Creates a `CSliceRef` from a `SliceRef`.
    /// This is a workaround for MSVC constructor limitation.
    static CSliceRef from(const SliceRef<T>& slice) noexcept {
        CSliceRef s;
        s._data = slice._data;
        s._size = slice._size;
        return s;
    }
#else
    CSliceRef(const SliceRef<T>& slice) noexcept {
        this->_data = slice._data;
        this->_size = slice._size;
    }
    /// Creates a `CSliceRef` from a `SliceRef`.
    /// This is a workaround for MSVC constructor limitation.
    static CSliceRef from(const SliceRef<T>& slice) noexcept {
        return CSliceRef(slice);
    }
#endif

    const T* _data;
    usize _size;

    SliceRef<T> operator()() const noexcept {
        return SliceRef<T>(this->_data, this->_size);
    }
};
static_assert(std::is_trivial<CSliceRef<usize>>::value);
static_assert(std::is_standard_layout<CSliceRef<usize>>::value);

// Alias is not a C type in MSVC, so this line doesn't work.
// ```c++
// using CByteSliceRef = CSliceRef<uint8_t>;
// ```
struct CByteSliceRef {
    CByteSliceRef() = _COPY_DELETE;
    CByteSliceRef(const CByteSliceRef&) = default;
    CByteSliceRef& operator=(const CByteSliceRef&) = default;

#if _MSC_VER
    /// Creates a `CByteSliceRef` from a `ByteSliceRef`.
    /// This is a workaround for MSVC constructor limitation.
    static CByteSliceRef from(const ByteSliceRef& slice) noexcept {
        CByteSliceRef s;
        s._data = slice._data;
        s._size = slice._size;
        return s;
    }
#else
    CByteSliceRef(const ByteSliceRef& slice) noexcept {
        this->_data = slice._data;
        this->_size = slice._size;
    }
    /// Creates a `CByteSliceRef` from a `ByteSliceRef`.
    /// This is a workaround for MSVC constructor limitation.
    static CByteSliceRef from(const ByteSliceRef& slice) noexcept {
        return CByteSliceRef(slice);
    }
#endif

    const uint8_t* _data;
    usize _size;

    ByteSliceRef operator()() const noexcept {
        ByteSliceRef slice;
        slice._data = this->_data;
        slice._size = this->_size;
        return slice;
    }
};
static_assert(std::is_trivial<CByteSliceRef>::value);
static_assert(std::is_standard_layout<CByteSliceRef>::value);

/// C++ counterpart of `Box<T>`
/// The ownership API is following `std::unique_ptr` design and the slice API is following `std::span` design.
template <typename T>
class BoxedSlice : public MutSliceRef<T> {
public:
    BoxedSlice() = delete;
    BoxedSlice(const BoxedSlice<T>&) = delete;
    BoxedSlice(BoxedSlice<T>&& s) noexcept : MutSliceRef<T>(s) {
        s._data = EMPTY_SLICE_BEGIN(T);
        s._size = 0;
    }
    BoxedSlice(std::nullptr_t) noexcept : MutSliceRef<T>() {}
    ~BoxedSlice() noexcept {
        if (this->_size > 0) {
            this->_drop();
        }
    }
    BoxedSlice<T>& operator=(BoxedSlice<T>&& b) noexcept {
        this->reset(b.release());
        return *this;
    }

    void _drop() noexcept;

    CBoxedSlice<T> into() noexcept;
    const CBoxedSlice<T>& as_c() const noexcept {
        return *reinterpret_cast<const CBoxedSlice<T>*>(this);
    }
    CBoxedSlice<T>& as_c() noexcept {
        return *reinterpret_cast<CBoxedSlice<T>*>(this);
    }

    void reset(_SliceRange<T> s) noexcept {
        if (this->_size > 0) {
            this->_drop();
        }
        this->_data = s._data;
        this->_size = s._size;
    }

    _SliceRange<T> release() noexcept {
        const auto range = this->get();
        this->_data = EMPTY_SLICE_BEGIN(T);
        this->_size = 0;
        return range;
    }

    /// Returns a mutable slice of the boxed slice.
    auto as_slice() noexcept {
        return MutSliceRef<T>(this->_data, this->_size);
    }

    /// Returns a read-only slice of the boxed slice.
    auto as_slice() const noexcept {
        return SliceRef<T>(this->_data, this->_size);
    }
};
static_assert(sizeof(usize) * 2 == sizeof(BoxedSlice<int>));
static_assert(std::is_standard_layout<BoxedSlice<usize>>::value);

/// C++ wrapper for a boxed slice with C ABI compatible layout.
///
/// @warning This type does *NOT* implement a safe destructor.
///          To avoid leak, see general note about C-prefixed types at the top of module documentation.
template <typename T>
struct [[nodiscard]] CBoxedSlice {
    CBoxedSlice() = _COPY_DELETE;
    CBoxedSlice(const CBoxedSlice&) = _COPY_DELETE;
    CBoxedSlice& operator=(const CBoxedSlice<T>&) = _COPY_DELETE;

#if _MSC_VER
    /// This is a workaround for MSVC constructor limitation.
    static CBoxedSlice from(BoxedSlice<T>&& slice) noexcept {
        auto r = slice.release();
        CBoxedSlice s;
        s._data = r._data;
        s._size = r._size;
        return s;
    }
#else
    CBoxedSlice(CBoxedSlice&&) = default;
    CBoxedSlice& operator=(CBoxedSlice<T>&&) = default;
    /// Constructs a `CBoxedSlice` by moving a `BoxedSlice`.
    CBoxedSlice(BoxedSlice<T>&& slice) noexcept {
        auto r = slice.release();
        this->_data = r._data;
        this->_size = r._size;
    }

    /// This is a workaround for MSVC constructor limitation.
    static CBoxedSlice from(BoxedSlice<T>&& slice) noexcept {
        return CBoxedSlice(std::move(slice));
    }
#endif

    T* _data;
    usize _size;

    /// Conversion operator to `BoxedSlice`.
    ///
    /// @note This conversion *MUST* be called unless the value is going to be passed to Rust side.
    BoxedSlice<T> operator()() noexcept {
        auto slice = BoxedSlice<T>(nullptr);
        auto r = this->release();
        slice._data = r._data;
        slice._size = r._size;
        return slice;
    }

    _SliceRange<T> get() const noexcept {
        return {this->_data, this->_size};
    }

    _SliceRange<T> release() noexcept {
        const auto range = this->get();
        this->_data = EMPTY_SLICE_BEGIN(T);
        this->_size = 0;
        return range;
    }
};
static_assert(std::is_trivial<CBoxedSlice<int>>::value);
static_assert(std::is_standard_layout<CBoxedSlice<int>>::value);

/// C++ unsafe counterpart of Rust `&str`.
///
/// Because `StrRef` in C++ side doesn't have any UTF-8 validation checking,
/// `CharStrRef` is an alternative of `StrRef` creation in C++ side.
/// The value can be converted to either `&[u8]` or `&str` with UTF-8 validation in Rust side.
struct CharStrRef {
    CharStrRef() = _COPY_DELETE;
    CharStrRef(const CharStrRef&) = default;
    CharStrRef& operator=(const CharStrRef&) = default;
    // #if !_MSC_VER
    CharStrRef(const char* head, usize size) noexcept : _data(_wrap_null(head)), _size(size) {}
    template <class R>
    CharStrRef(SAFE_R range) noexcept : _data(_wrap_null(ranges::data(range))), _size(ranges::size(range)) {}
    CharStrRef(std::nullptr_t) noexcept : _data(EMPTY_SLICE_BEGIN(const char)), _size(0) {}
    // #endif

    const char* _data;
    usize _size;

    // constants and types
    using element_type = const char;
    using value_type = typename std::remove_cv_t<const char>;
    using size_type = uintptr_t;
    using difference_type = intptr_t;
    using pointer = element_type*;
    using const_pointer = const element_type*;
    using reference = element_type&;
    using const_reference = const element_type&;
    using iterator = typename std::string_view::iterator;
    using reverse_iterator = std::reverse_iterator<iterator>;

    // observers
    size_type size() const noexcept {
        return this->_size;
    }
    size_type size_bytes() const noexcept {
        return this->size() * sizeof(element_type);
    }
    bool empty() const noexcept {
        return this->size() == 0;
    }

    // element access
    reference operator[](size_type idx) const noexcept {
        assert(idx < this->size());
        return this->data()[idx];
    }
    reference front() const noexcept {
        return this->data()[0];
    }
    reference back() const noexcept {
        return this->data()[size() - 1];
    }
    pointer data() const noexcept {
        return this->_data;
    }

    // iterator
    iterator begin() const noexcept {
        return view().begin();
    }
    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());
    }

    _SliceRange<element_type> get() const noexcept {
        return {data(), size()};
    }

#if __cpp_lib_span
    /// Returns the slice as a `std::span`.
    std::span<element_type> span() const noexcept {
        return std::span<element_type>(data(), size());
    }
#endif

    StrRef as_str_unchecked() const noexcept;

#if __cpp_lib_string_view
    /// Constructs a `CharStrRef` from a null-terminated string.
    CharStrRef(const char* s) noexcept : CharStrRef(std::string_view(s)) {}

    /// Returns a `std::string_view` of the string.
    std::string_view view() const noexcept {
        return std::string_view(this->data(), this->size());
    }

    /// Conversion operator to `std::string_view`.
    operator std::string_view() const noexcept {
        return this->view();
    }

    /// Create a `std::string` by copying data.
    /// @return The newly created `std::string`.
    std::string to_string() const noexcept {
        return std::string(this->view());
    }
#endif
};
static_assert(sizeof(SliceRef<char>) == sizeof(CharStrRef));
static_assert(std::is_trivial<CharStrRef>::value);
static_assert(std::is_standard_layout<CharStrRef>::value);

/// C++ counterpart of Rust `&str`.
///
/// Because `StrRef` in C++ side doesn't have any UTF-8 validation checking,
/// this type is highly recommended to be created from Rust side.
///
/// To create `StrRef` in C++ side, use `ByteSliceRef::as_str_unchecked()` or `CharStrRef::as_str_unchecked()`
/// at your own risk.
struct StrRef : public CharStrRef {
    StrRef() = delete;
    StrRef(const StrRef&) = default;
    StrRef(const BoxedStr&) noexcept;
    StrRef(std::nullptr_t) noexcept : CharStrRef(EMPTY_SLICE_BEGIN(const char), 0) {}

    StrRef& operator=(const StrRef&) = default;
};
static_assert(std::is_trivially_copyable<StrRef>::value);
static_assert(std::is_standard_layout<StrRef>::value);

/// C++ wrapper for a str with C ABI compatible layout.
struct CStrRef {
    CStrRef() = _COPY_DELETE;
    CStrRef(const CStrRef&) = default;
    CStrRef& operator=(const CStrRef&) = default;

#if !_MSC_VER
    CStrRef(const StrRef& slice) noexcept {
        this->_data = slice.data();
        this->_size = slice.size();
    }
#endif

    const char* _data;
    usize _size;

    StrRef operator()() const noexcept {
        auto s = StrRef(nullptr);
        s._data = this->_data;
        s._size = this->_size;
        return s;
    }
};
static_assert(std::is_trivial<CStrRef>::value);
static_assert(std::is_standard_layout<CStrRef>::value);

/// C++ counterpart of Rust `Box<str>`.
class BoxedStr : public StrRef {
public:
    BoxedStr() = delete;
    BoxedStr(BoxedStr&) = delete;
    BoxedStr(BoxedStr&& s) noexcept : StrRef(s) {
        s._data = EMPTY_SLICE_BEGIN(const char);
        s._size = 0;
    }
    BoxedStr(std::nullptr_t) noexcept : StrRef(nullptr) {}

    ~BoxedStr() noexcept {
        if (this->_size > 0) {
            this->_drop();
        }
    }

    BoxedStr& operator=(BoxedStr&& b) noexcept {
        this->reset(b.release());
        return *this;
    }

    void _drop() noexcept;

    void reset(_SliceRange<const char> s) noexcept {
        if (this->_size > 0) {
            this->_drop();
        }
        this->_data = s._data;
        this->_size = s._size;
    }

    _SliceRange<const char> release() noexcept {
        const auto range = this->get();
        this->_data = EMPTY_SLICE_BEGIN(const char);
        this->_size = 0;
        return range;
    }

    StrRef as_str() const noexcept {
        return this->as_str_unchecked();
    }
};
static_assert(sizeof(StrRef) == sizeof(BoxedStr));
static_assert(std::is_standard_layout<BoxedStr>::value);

/// C++ wrapper for Rust `Box<str>` with C ABI compatible layout.
///
/// @warning This type does *NOT* implement a safe destructor.
///          To avoid leak, see general note about C-prefixed types at the top of module documentation.
struct [[nodiscard]] CBoxedStr {
    CBoxedStr() = _COPY_DELETE;
    CBoxedStr(const CBoxedStr&) = _COPY_DELETE;
    CBoxedStr& operator=(const CBoxedStr&) = _COPY_DELETE;

    const char* _data;
    usize _size;

#if _MSC_VER
    /// This is a workaround for MSVC constructor limitation.
    static CBoxedStr from(BoxedStr&& str) noexcept {
        auto r = str.release();
        CBoxedStr s;
        s._data = r._data;
        s._size = r._size;
        return s;
    }
#else
    CBoxedStr(CBoxedStr&&) = default;
    CBoxedStr& operator=(CBoxedStr&&) = default;
    CBoxedStr(BoxedStr&& str) noexcept {
        auto r = str.release();
        this->_data = r._data;
        this->_size = r._size;
    }

    /// This is a workaround for MSVC constructor limitation.
    static CBoxedStr from(BoxedStr&& slice) noexcept {
        return CBoxedStr(std::move(slice));
    }
#endif

    BoxedStr operator()() noexcept {
        auto slice = BoxedStr(nullptr);
        auto r = this->release();
        slice._data = r._data;
        slice._size = r._size;
        return slice;
    }

    _SliceRange<const char> release() noexcept {
        const auto range = _SliceRange<const char>{_data, _size};
        this->_data = EMPTY_SLICE_BEGIN(const char);
        this->_size = 0;
        return range;
    }
};
static_assert(std::is_trivial<CBoxedStr>::value);
static_assert(std::is_standard_layout<CBoxedStr>::value);

template <typename T>
inline CMutSliceRef<T> MutSliceRef<T>::into() const noexcept {
    return CMutSliceRef<T>::from(*this);
}

template <typename T>
inline typename std::conditional<std::is_same_v<T, uint8_t>, CByteSliceRef, CSliceRef<T>>::type SliceRef<T>::into()
        const noexcept {
    if constexpr (std::is_same_v<T, uint8_t>) {
        return CByteSliceRef::from(*this);
    } else {
        return CSliceRef<T>::from(*this);
    }
}

template <typename T>
inline CBoxedSlice<T> BoxedSlice<T>::into() noexcept {
    return CBoxedSlice<T>::from(std::move(*this));
}

inline StrRef::StrRef(const BoxedStr& owned) noexcept : CharStrRef(owned._data, owned._size) {}

inline StrRef CharStrRef::as_str_unchecked() const noexcept {
    return *reinterpret_cast<const StrRef*>(this);
}
template <>
template <>
inline CharStrRef MutSliceRef<const uint8_t>::as_char_str<const uint8_t>() const noexcept {
    return CharStrRef(reinterpret_cast<const char*>(this->_data), this->_size);
}
template <>
template <>
inline StrRef MutSliceRef<const uint8_t>::as_str_unchecked<const uint8_t>() const noexcept {
    return as_char_str().as_str_unchecked();
}

#undef SAFE_R
#undef EMPTY_SLICE_BEGIN

}  // namespace ffi_types
#pragma once


//! This header is intended to be included in rust_types.hh file.
    

namespace ffi_types {

extern "C" {

void _rust_ffi_boxed_str_drop(ffi_types::CBoxedStr _string);

void _rust_ffi_boxed_bytes_drop(ffi_types::CBoxedSlice<uint8_t> _slice);

} // extern "C"

} // namespace ffi_types
namespace ffi_types {

inline void BoxedStr::_drop() noexcept {
    ffi_types::_rust_ffi_boxed_str_drop(CBoxedStr::from(std::move(*this)));
}

template <>
inline void BoxedSlice<uint8_t>::_drop() noexcept {
    ffi_types::_rust_ffi_boxed_bytes_drop(CBoxedSlice<uint8_t>::from(std::move(*this)));
}

}  // namespace ffi_types
#undef _COPY_DELETE

namespace rust {
using namespace ffi_types;
}