#pragma once

#include <xrpl/basics/base_uint.h>
#include <xrpl/ledger/ReadView.h>
#include <xrpl/protocol/Keylet.h>
#include <xrpl/protocol/STLedgerEntry.h>
#include <xrpl/protocol/STVector256.h>

#include <cstddef>
#include <iterator>
#include <optional>
#include <vector>

namespace xrpl {

/**
 * A class that simplifies iterating ledger directory pages
 *
 * The Dir class provides a forward iterator for walking through
 * the uint256 values contained in ledger directories.
 *
 * The Dir class also allows accelerated directory walking by
 * stepping directly from one page to the next using the next_page()
 * member function.
 *
 * As of July 2024, the Dir class is only being used with NFTokenOffer
 * directories and for unit tests.
 */
class Dir
{
private:
    ReadView const* view_ = nullptr;
    Keylet root_;
    SLE::const_pointer sle_;
    STVector256 const* indexes_ = nullptr;

public:
    class ConstIterator;
    using value_type = SLE::const_pointer;

    Dir(ReadView const&, Keylet const&);

    [[nodiscard]] ConstIterator
    begin() const;

    [[nodiscard]] ConstIterator
    end() const;
};

class Dir::ConstIterator
{
public:
    using value_type = Dir::value_type;
    using pointer = value_type const*;
    using reference = value_type const&;
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::forward_iterator_tag;

    bool
    operator==(ConstIterator const& other) const;

    bool
    operator!=(ConstIterator const& other) const
    {
        return !(*this == other);
    }

    reference
    operator*() const;

    pointer
    operator->() const
    {
        return &**this;
    }

    ConstIterator&
    operator++();

    ConstIterator
    operator++(int);

    ConstIterator&
    nextPage();

    std::size_t
    pageSize();

    Keylet const&
    page() const
    {
        return page_;
    }

    uint256
    index() const
    {
        return index_;
    }

private:
    friend class Dir;

    ConstIterator(ReadView const& view, Keylet const& root, Keylet const& page)
        : view_(&view), root_(root), page_(page)
    {
    }

    ReadView const* view_ = nullptr;
    Keylet root_;
    Keylet page_;
    uint256 index_;
    std::optional<value_type> mutable cache_;
    SLE::const_pointer sle_;
    STVector256 const* indexes_ = nullptr;
    std::vector<uint256>::const_iterator it_;
};

}  // namespace xrpl