// This file Copyright © Mnemosyne LLC.
// It may be used under GPLv2 (SPDX: GPL-2.0-only), GPLv3 (SPDX: GPL-3.0-only),
// or any future license endorsed by Mnemosyne LLC.
// License text can be found in the licenses/ folder.

#pragma once

#ifndef __TRANSMISSION__
#error only libtransmission should #include this header.
#endif

#include <cstddef> // size_t
#include <cstdint> // uint8_t, uint64_t
#include <ctime>
#include <limits>
#include <optional>
#include <string>
#include <vector>

#include "libtransmission/transmission.h" // tr_block_span_t (ptr only)

#include "libtransmission/blocklist.h"
#include "libtransmission/handshake.h"
#include "libtransmission/net.h" /* tr_address */
#include "libtransmission/tr-assert.h"
#include "libtransmission/utils.h" /* tr_compare_3way */

/**
 * @addtogroup peers Peers
 * @{
 */

class tr_peer_socket;
struct tr_peer;
struct tr_peerMgr;
struct tr_peer_stat;
struct tr_session;
struct tr_torrent;

/* added_f's bitwise-or'ed flags */
enum
{
    /* true if the peer supports encryption */
    ADDED_F_ENCRYPTION_FLAG = 1,
    /* true if the peer is a seed or partial seed */
    ADDED_F_UPLOAD_ONLY_FLAG = 2,
    /* true if the peer supports µTP */
    ADDED_F_UTP_FLAGS = 4,
    /* true if the peer has holepunch support */
    ADDED_F_HOLEPUNCH = 8,
    /* true if the peer telling us about this peer
     * initiated the connection (implying that it is connectible) */
    ADDED_F_CONNECTABLE = 16
};

/**
 * Peer information that should be retained even when not connected,
 * e.g. to help us decide which peers to connect to.
 */
class tr_peer_info
{
public:
    tr_peer_info(tr_socket_address socket_address, uint8_t pex_flags, tr_peer_from from)
        : listen_socket_address_{ socket_address }
        , from_first_{ from }
        , from_best_{ from }
    {
        TR_ASSERT(!std::empty(socket_address.port()));
        ++n_known_connectable;
        set_pex_flags(pex_flags);
    }

    tr_peer_info(tr_address address, uint8_t pex_flags, tr_peer_from from)
        : listen_socket_address_{ address, tr_port{} }
        , from_first_{ from }
        , from_best_{ from }
    {
        set_pex_flags(pex_flags);
    }

    tr_peer_info(tr_peer_info&&) = delete;
    tr_peer_info(tr_peer_info const&) = delete;
    tr_peer_info& operator=(tr_peer_info&&) = delete;
    tr_peer_info& operator=(tr_peer_info const&) = delete;

    ~tr_peer_info()
    {
        if (!std::empty(listen_socket_address_.port()))
        {
            [[maybe_unused]] auto const n_prev = n_known_connectable--;
            TR_ASSERT(n_prev > 0U);
        }
    }

    [[nodiscard]] static auto known_connectable_count() noexcept
    {
        return n_known_connectable;
    }

    // ---

    [[nodiscard]] constexpr auto const& listen_socket_address() const noexcept
    {
        return listen_socket_address_;
    }

    [[nodiscard]] constexpr auto const& listen_address() const noexcept
    {
        return listen_socket_address_.address();
    }

    [[nodiscard]] constexpr auto listen_port() const noexcept
    {
        return listen_socket_address_.port();
    }

    void set_listen_port(tr_port port_in) noexcept
    {
        if (!std::empty(port_in))
        {
            auto& port = listen_socket_address_.port_;
            if (std::empty(port)) // increment known connectable peers if we did not know the listening port of this peer before
            {
                ++n_known_connectable;
            }
            port = port_in;
        }
    }

    [[nodiscard]] auto display_name() const
    {
        return listen_socket_address_.display_name();
    }

    // ---

    [[nodiscard]] constexpr auto from_first() const noexcept
    {
        return from_first_;
    }

    [[nodiscard]] constexpr auto from_best() const noexcept
    {
        return from_best_;
    }

    constexpr void found_at(tr_peer_from from) noexcept
    {
        from_best_ = std::min(from_best_, from);
    }

    // ---

    constexpr void set_seed(bool seed = true) noexcept
    {
        is_seed_ = seed;
    }

    [[nodiscard]] constexpr auto is_seed() const noexcept
    {
        return is_seed_;
    }

    constexpr void set_upload_only(bool value = true) noexcept
    {
        is_upload_only_ = value;
    }

    [[nodiscard]] constexpr auto is_upload_only() const noexcept
    {
        return is_upload_only_ || is_seed();
    }

    // ---

    void set_connectable(bool value = true) noexcept
    {
        is_connectable_ = value;
    }

    [[nodiscard]] constexpr auto const& is_connectable() const noexcept
    {
        return is_connectable_;
    }

    // ---

    void set_utp_supported(bool value = true) noexcept
    {
        is_utp_supported_ = value;
    }

    [[nodiscard]] constexpr auto supports_utp() const noexcept
    {
        return is_utp_supported_;
    }

    // ---

    void set_encryption_preferred(bool value = true) noexcept
    {
        is_encryption_preferred_ = value;
    }

    [[nodiscard]] constexpr auto const& prefers_encryption() const noexcept
    {
        return is_encryption_preferred_;
    }

    // ---

    void set_holepunch_supported(bool value = true) noexcept
    {
        is_holepunch_supported_ = value;
    }

    [[nodiscard]] constexpr auto const& supports_holepunch() const noexcept
    {
        return is_holepunch_supported_;
    }

    // ---

    [[nodiscard]] constexpr auto compare_by_fruitless_count(tr_peer_info const& that) const noexcept
    {
        return tr_compare_3way(num_consecutive_fruitless_, that.num_consecutive_fruitless_);
    }

    [[nodiscard]] constexpr auto compare_by_piece_data_time(tr_peer_info const& that) const noexcept
    {
        return tr_compare_3way(piece_data_at_, that.piece_data_at_);
    }

    // ---

    constexpr auto set_connected(time_t now, bool is_connected = true, bool is_disconnecting = false) noexcept
    {
        if (is_connected_ == is_connected)
        {
            return;
        }

        connection_changed_at_ = now;

        is_connected_ = is_connected;

        if (is_connected_)
        {
            piece_data_at_ = {};
        }
        else if (has_transferred_piece_data())
        {
            num_consecutive_fruitless_ = {};
        }
        else if (is_disconnecting)
        {
            on_fruitless_connection();
        }
    }

    [[nodiscard]] constexpr auto is_connected() const noexcept
    {
        return is_connected_;
    }

    [[nodiscard]] auto has_handshake() const noexcept
    {
        return static_cast<bool>(outgoing_handshake_);
    }

    template<typename... Args>
    void start_handshake(Args&&... args)
    {
        TR_ASSERT(!outgoing_handshake_);
        if (!outgoing_handshake_)
        {
            outgoing_handshake_ = std::make_unique<tr_handshake>(std::forward<Args>(args)...);
        }
    }

    void destroy_handshake() noexcept
    {
        outgoing_handshake_.reset();
    }

    [[nodiscard]] auto is_in_use() const noexcept
    {
        return is_connected() || has_handshake();
    }

    // ---

    [[nodiscard]] bool is_blocklisted(libtransmission::Blocklists const& blocklist) const
    {
        if (!blocklisted_.has_value())
        {
            blocklisted_ = blocklist.contains(listen_address());
        }

        return *blocklisted_;
    }

    void set_blocklisted_dirty()
    {
        blocklisted_.reset();
    }

    // ---

    constexpr void ban() noexcept
    {
        is_banned_ = true;
    }

    [[nodiscard]] constexpr auto is_banned() const noexcept
    {
        return is_banned_;
    }

    // ---

    [[nodiscard]] constexpr auto connection_attempt_time() const noexcept
    {
        return connection_attempted_at_;
    }

    constexpr void set_connection_attempt_time(time_t value) noexcept
    {
        connection_attempted_at_ = value;
    }

    constexpr void set_latest_piece_data_time(time_t value) noexcept
    {
        piece_data_at_ = value;
    }

    [[nodiscard]] constexpr bool has_transferred_piece_data() const noexcept
    {
        return piece_data_at_ != time_t{};
    }

    [[nodiscard]] constexpr auto reconnect_interval_has_passed(time_t const now) const noexcept
    {
        auto const interval = now - std::max(connection_attempted_at_, connection_changed_at_);
        return interval >= get_reconnect_interval_secs(now);
    }

    [[nodiscard]] constexpr std::optional<time_t> idle_secs(time_t now) const noexcept
    {
        if (!is_connected_)
        {
            return {};
        }

        return now - std::max(piece_data_at_, connection_changed_at_);
    }

    [[nodiscard]] auto is_inactive(time_t const now) const noexcept
    {
        return !is_in_use() && now > 0 && connection_changed_at_ > 0 && now - connection_changed_at_ >= InactiveThresSecs;
    }

    // ---

    constexpr void on_fruitless_connection() noexcept
    {
        if (num_consecutive_fruitless_ != std::numeric_limits<decltype(num_consecutive_fruitless_)>::max())
        {
            ++num_consecutive_fruitless_;
        }
    }

    [[nodiscard]] constexpr auto fruitless_connection_count() const noexcept
    {
        return num_consecutive_fruitless_;
    }

    // ---

    constexpr void set_pex_flags(uint8_t pex_flags) noexcept
    {
        pex_flags_ = pex_flags;

        if ((pex_flags & ADDED_F_CONNECTABLE) != 0U)
        {
            set_connectable();
        }

        if ((pex_flags & ADDED_F_UTP_FLAGS) != 0U)
        {
            set_utp_supported();
        }

        if ((pex_flags & ADDED_F_ENCRYPTION_FLAG) != 0U)
        {
            set_encryption_preferred();
        }

        if ((pex_flags & ADDED_F_HOLEPUNCH) != 0U)
        {
            set_holepunch_supported();
        }

        if ((pex_flags & ADDED_F_UPLOAD_ONLY_FLAG) != 0U)
        {
            set_upload_only();
        }
    }

    [[nodiscard]] constexpr uint8_t pex_flags() const noexcept
    {
        auto ret = pex_flags_;

        if (is_connectable_)
        {
            if (*is_connectable_)
            {
                ret |= ADDED_F_CONNECTABLE;
            }
            else
            {
                ret &= ~ADDED_F_CONNECTABLE;
            }
        }

        if (is_utp_supported_)
        {
            if (*is_utp_supported_)
            {
                ret |= ADDED_F_UTP_FLAGS;
            }
            else
            {
                ret &= ~ADDED_F_UTP_FLAGS;
            }
        }

        if (is_encryption_preferred_)
        {
            if (*is_encryption_preferred_)
            {
                ret |= ADDED_F_ENCRYPTION_FLAG;
            }
            else
            {
                ret &= ~ADDED_F_ENCRYPTION_FLAG;
            }
        }

        if (is_holepunch_supported_)
        {
            if (*is_holepunch_supported_)
            {
                ret |= ADDED_F_HOLEPUNCH;
            }
            else
            {
                ret &= ~ADDED_F_HOLEPUNCH;
            }
        }

        if (is_upload_only())
        {
            ret |= ADDED_F_UPLOAD_ONLY_FLAG;
        }
        else
        {
            ret &= ~ADDED_F_UPLOAD_ONLY_FLAG;
        }

        return ret;
    }

    // ---

    // merge two peer info objects that supposedly describes the same peer
    void merge(tr_peer_info& that) noexcept;

private:
    [[nodiscard]] constexpr time_t get_reconnect_interval_secs(time_t const now) const noexcept
    {
        // if we were recently connected to this peer and transferring piece
        // data, try to reconnect to them sooner rather that later -- we don't
        // want network troubles to get in the way of a good peer.
        auto const unreachable = is_connectable_ && !*is_connectable_;
        if (!unreachable && now - piece_data_at_ <= MinimumReconnectIntervalSecs * 2)
        {
            return MinimumReconnectIntervalSecs;
        }

        // otherwise, the interval depends on how many times we've tried
        // and failed to connect to the peer. Penalize peers that were
        // unreachable the last time we tried
        auto step = num_consecutive_fruitless_;
        if (unreachable)
        {
            step += 2;
        }

        switch (step)
        {
        case 0:
            return 0U;
        case 1:
            return 10U;
        case 2:
            return 60U * 2U;
        case 3:
            return 60U * 15U;
        case 4:
            return 60U * 30U;
        case 5:
            return 60U * 60U;
        default:
            return 60U * 120U;
        }
    }

    // the minimum we'll wait before attempting to reconnect to a peer
    static auto constexpr MinimumReconnectIntervalSecs = time_t{ 5U };
    static auto constexpr InactiveThresSecs = time_t{ 60 * 60 };

    static auto inline n_known_connectable = size_t{};

    // if the port is 0, it SHOULD mean we don't know this peer's listen socket address
    tr_socket_address listen_socket_address_;

    time_t connection_attempted_at_ = {};
    time_t connection_changed_at_ = {};
    time_t piece_data_at_ = {};

    mutable std::optional<bool> blocklisted_;
    std::optional<bool> is_connectable_;
    std::optional<bool> is_utp_supported_;
    std::optional<bool> is_encryption_preferred_;
    std::optional<bool> is_holepunch_supported_;

    tr_peer_from const from_first_; // where the peer was first found
    tr_peer_from from_best_; // the "best" place where this peer was found

    uint8_t num_consecutive_fruitless_ = {};
    uint8_t pex_flags_ = {};

    bool is_banned_ = false;
    bool is_connected_ = false;
    bool is_seed_ = false;
    bool is_upload_only_ = false;

    std::unique_ptr<tr_handshake> outgoing_handshake_;
};

struct tr_pex
{
    tr_pex() = default;

    explicit tr_pex(tr_socket_address socket_address_in, uint8_t flags_in = {})
        : socket_address{ socket_address_in }
        , flags{ flags_in }
    {
    }

    template<typename OutputIt>
    OutputIt to_compact(OutputIt out) const
    {
        return socket_address.to_compact(out);
    }

    template<typename OutputIt>
    static OutputIt to_compact(OutputIt out, tr_pex const* pex, size_t n_pex)
    {
        for (size_t i = 0; i < n_pex; ++i)
        {
            out = pex[i].to_compact(out);
        }
        return out;
    }

    [[nodiscard]] static std::vector<tr_pex> from_compact_ipv4(
        void const* compact,
        size_t compact_len,
        uint8_t const* added_f,
        size_t added_f_len);

    [[nodiscard]] static std::vector<tr_pex> from_compact_ipv6(
        void const* compact,
        size_t compact_len,
        uint8_t const* added_f,
        size_t added_f_len);

    [[nodiscard]] std::string display_name() const
    {
        return socket_address.display_name();
    }

    [[nodiscard]] int compare(tr_pex const& that) const noexcept // <=>
    {
        return socket_address.compare(that.socket_address);
    }

    [[nodiscard]] bool operator==(tr_pex const& that) const noexcept
    {
        return compare(that) == 0;
    }

    [[nodiscard]] bool operator<(tr_pex const& that) const noexcept
    {
        return compare(that) < 0;
    }

    [[nodiscard]] bool is_valid() const noexcept
    {
        return socket_address.is_valid();
    }

    [[nodiscard]] bool is_valid_for_peers(tr_peer_from from) const noexcept
    {
        return socket_address.is_valid_for_peers(from);
    }

    tr_socket_address socket_address;

    uint8_t flags = 0;
};

constexpr bool tr_isPex(tr_pex const* pex)
{
    return pex != nullptr && pex->socket_address.is_valid();
}

[[nodiscard]] tr_peerMgr* tr_peerMgrNew(tr_session* session);

void tr_peerMgrFree(tr_peerMgr* manager);

[[nodiscard]] std::vector<tr_block_span_t> tr_peerMgrGetNextRequests(tr_torrent* torrent, tr_peer const* peer, size_t numwant);

void tr_peerMgrAddIncoming(tr_peerMgr* manager, tr_peer_socket&& socket);

size_t tr_peerMgrAddPex(tr_torrent* tor, tr_peer_from from, tr_pex const* pex, size_t n_pex);

enum
{
    TR_PEERS_CONNECTED,
    TR_PEERS_INTERESTING
};

[[nodiscard]] std::vector<tr_pex> tr_peerMgrGetPeers(
    tr_torrent const* tor,
    uint8_t address_type,
    uint8_t peer_list_mode,
    size_t max_peer_count);

void tr_peerMgrAddTorrent(tr_peerMgr* manager, struct tr_torrent* tor);

// return the number of connected peers that have `piece`, or -1 if we already have it
[[nodiscard]] int8_t tr_peerMgrPieceAvailability(tr_torrent const* tor, tr_piece_index_t piece);

void tr_peerMgrTorrentAvailability(tr_torrent const* tor, int8_t* tab, unsigned int n_tabs);

[[nodiscard]] uint64_t tr_peerMgrGetDesiredAvailable(tr_torrent const* tor);

[[nodiscard]] struct tr_peer_stat* tr_peerMgrPeerStats(tr_torrent const* tor, size_t* setme_count);

[[nodiscard]] tr_webseed_view tr_peerMgrWebseed(tr_torrent const* tor, size_t i);

/* @} */