//===-- LibCxxSpan.cpp ----------------------------------------------------===//

//

// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.

// See https://llvm.org/LICENSE.txt for license information.

// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

//

//===----------------------------------------------------------------------===//

#include "LibCxx.h"

#include "lldb/Core/ValueObject.h"

#include "lldb/DataFormatters/FormattersHelpers.h"

#include "lldb/Utility/ConstString.h"

#include "llvm/ADT/APSInt.h"

#include <optional>

using namespace lldb;

using namespace lldb_private;

using namespace lldb_private::formatters;

namespace lldb_private {

namespace formatters {

class LibcxxStdSpanSyntheticFrontEnd : public SyntheticChildrenFrontEnd {

public:

  LibcxxStdSpanSyntheticFrontEnd(lldb::ValueObjectSP valobj_sp);

  ~LibcxxStdSpanSyntheticFrontEnd() override = default;

  size_t CalculateNumChildren() override;

  lldb::ValueObjectSP GetChildAtIndex(size_t idx) override;

  /// Determines properties of the std::span<> associated with this object

  //

  // std::span can either be instantiated with a compile-time known

  // extent or a std::dynamic_extent (this is the default if only the

  // type template argument is provided). The layout of std::span

  // depends on whether the extent is dynamic or not. For static

  // extents (e.g., std::span<int, 9>):

  //

  // (std::__1::span<const int, 9>) s = {

  //   __data = 0x000000016fdff494

  // }

  //

  // For dynamic extents, e.g., std::span<int>, the layout is:

  //

  // (std::__1::span<const int, 18446744073709551615>) s = {

  //   __data = 0x000000016fdff494

  //   __size = 6

  // }

  //

  // This function checks for a '__size' member to determine the number

  // of elements in the span. If no such member exists, we get the size

  // from the only other place it can be: the template argument.

  bool Update() override;

  bool MightHaveChildren() override;

  size_t GetIndexOfChildWithName(ConstString name) override;

private:

  ValueObject *m_start = nullptr; ///< First element of span. Held, not owned.

  CompilerType m_element_type{};  ///< Type of span elements.

  size_t m_num_elements = 0;      ///< Number of elements in span.

  uint32_t m_element_size = 0;    ///< Size in bytes of each span element.

};

lldb_private::formatters::LibcxxStdSpanSyntheticFrontEnd::

    LibcxxStdSpanSyntheticFrontEnd(lldb::ValueObjectSP valobj_sp)

    : SyntheticChildrenFrontEnd(*valobj_sp) {

  if (valobj_sp)

    Update();

}

size_t lldb_private::formatters::LibcxxStdSpanSyntheticFrontEnd::

    CalculateNumChildren() {

  return m_num_elements;

}

lldb::ValueObjectSP

lldb_private::formatters::LibcxxStdSpanSyntheticFrontEnd::GetChildAtIndex(

    size_t idx) {

  if (!m_start)

    return {};

  uint64_t offset = idx * m_element_size;

  offset = offset + m_start->GetValueAsUnsigned(0);

  StreamString name;

  name.Printf("[%" PRIu64 "]", (uint64_t)idx);

  return CreateValueObjectFromAddress(name.GetString(), offset,

                                      m_backend.GetExecutionContextRef(),

                                      m_element_type);

}

bool lldb_private::formatters::LibcxxStdSpanSyntheticFrontEnd::Update() {

  // Get element type.

  ValueObjectSP data_type_finder_sp = GetChildMemberWithName(

      m_backend, {ConstString("__data_"), ConstString("__data")});

  if (!data_type_finder_sp)

    return false;

  m_element_type = data_type_finder_sp->GetCompilerType().GetPointeeType();

  // Get element size.

  if (std::optional<uint64_t> size = m_element_type.GetByteSize(nullptr)) {

    m_element_size = *size;

    // Get data.

    if (m_element_size > 0) {

      m_start = data_type_finder_sp.get();

    }

    // Get number of elements.

    if (auto size_sp = GetChildMemberWithName(

            m_backend, {ConstString("__size_"), ConstString("__size")})) {

      m_num_elements = size_sp->GetValueAsUnsigned(0);

    } else if (auto arg =

                   m_backend.GetCompilerType().GetIntegralTemplateArgument(1)) {

      m_num_elements = arg->value.getLimitedValue();

    }

  }

  return true;

}

bool lldb_private::formatters::LibcxxStdSpanSyntheticFrontEnd::

    MightHaveChildren() {

  return true;

}

size_t lldb_private::formatters::LibcxxStdSpanSyntheticFrontEnd::

    GetIndexOfChildWithName(ConstString name) {

  if (!m_start)

    return UINT32_MAX;

  return ExtractIndexFromString(name.GetCString());

}

lldb_private::SyntheticChildrenFrontEnd *

LibcxxStdSpanSyntheticFrontEndCreator(CXXSyntheticChildren *,

                                      lldb::ValueObjectSP valobj_sp) {

  if (!valobj_sp)

    return nullptr;

  CompilerType type = valobj_sp->GetCompilerType();

  if (!type.IsValid() || type.GetNumTemplateArguments() != 2)

    return nullptr;

  return new LibcxxStdSpanSyntheticFrontEnd(valobj_sp);

}

} // namespace formatters

} // namespace lldb_private