pagination.hpp

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#pragma once
 
#include "kalshi/error.hpp"
 
#include <cstddef>
#include <limits>
#include <optional>
#include <string>
#include <string_view>
#include <type_traits>
#include <utility>
#include <vector>
 
namespace kalshi {
 
template <class Fetch, class Response, class Items>
[[nodiscard]] Result<std::vector<typename Items::value_type>>
collect_pages(Fetch&& fetch, Items Response::*items,
              std::size_t max_pages = std::numeric_limits<std::size_t>::max()) {
    std::vector<typename Items::value_type> all;
    std::string cursor;
    for (std::size_t page = 0; page < max_pages; ++page) {
        Result<Response> response = fetch(std::string_view{cursor});
        if (!response) {
            return std::unexpected(std::move(response.error()));
        }
        Items& batch = (*response).*items;
        all.insert(all.end(), std::make_move_iterator(batch.begin()),
                   std::make_move_iterator(batch.end()));
        std::string next;
        if constexpr (std::is_same_v<decltype(response->cursor), std::optional<std::string>>) {
            next = response->cursor.value_or("");
        } else {
            next = std::move(response->cursor);
        }
        if (next.empty()) {
            break;
        }
        if (next == cursor) {
            return std::unexpected(
                Error{ErrorCode::ParseError, "Pagination cursor did not advance: " + next, 0, {}});
        }
        cursor = std::move(next);
    }
    return all;
}
 
} // namespace kalshi