/* ************************************************************************** */
/*                                                                            */
/*                                                        :::      ::::::::   */
/*   EventToken.hpp                                     :+:      :+:    :+:   */
/*                                                    +:+ +:+         +:+     */
/*   By: acossari <acossari@student.codam.nl>       +#+  +:+       +#+        */
/*                                                +#+#+#+#+#+   +#+           */
/*   Created: 2026/08/25 13:26:42 by acossari          #+#    #+#             */
/*   Updated: 2026/08/25 19:06:13 by acossari         ###   ########.fr       */
/*                                                                            */
/* ************************************************************************** */

#pragma once

#include <cstdint>

namespace webserv {

enum class EndpointKind {
  ClientSocket,
  CgiStdin,
  CgiStdout,
  Listener,
};

// Identifies which registered endpoint produced an epoll event without storing
// a pointer. For Listener, index selects a listener; for every other kind it
// selects a connection slot, while kind identifies its client socket or CGI
// pipe. epoll_wait() returns a batch in which an old event may remain after its
// endpoint has been retired and re-registered. generation distinguishes that
// old registration from the current one even when index and kind are equal.
//
// Packed layout in epoll_event.data.u64:
// bits  0-29 | index      | 30 bits
// bits 30-31 | kind       |  2 bits
// bits 32-63 | generation | 32 bits
struct EventToken {
    static constexpr std::uint64_t INDEX_BITS = 30;
    static constexpr std::uint64_t KIND_BITS = 2;

    // List-initialization gives 1 the exact std::uint32_t type before shifting.
    // std::uint32_t{1} << INDEX_BITS       = 1,073,741,824
    // (std::uint32_t{1} << INDEX_BITS) - 1 = 1,073,741,823
    // Binary: 100...000 (30 zeros) - 1 = 011...111 (30 ones).
    static constexpr std::uint32_t MAX_INDEX =
        (std::uint32_t{1} << INDEX_BITS) - 1;

    std::uint32_t index;
    EndpointKind kind;
    std::uint32_t generation;
};

std::uint64_t pack(EventToken token);
EventToken unpack(std::uint64_t token);

}  // namespace webserv