#pragma once

/** A peer of a bound (server) instance of UdpVpn */

#include <netinet/in.h>
#include <bitset>
#include <chrono>
#include "util.hpp"
#include "VpnPacket.hpp"
#include "congestion_control.hpp"

class UdpVpn;

const int PACKET_LOSS_WINDOW = 128, PACKET_LOST_AFTER = 8;

class PacketLossLogger {
    public:
        PacketLossLogger();
        void log_packet(uint32_t seqno);
        double get_loss_rate() const {
            return (double)(_win_start_losses - _last_window_losses)
                / (double)PACKET_LOSS_WINDOW;
        }

        const std::bitset<PACKET_LOST_AFTER> get_received_ahead() const {
            return _received_ahead;
        }

        uint32_t get_cur_seqno() const { return _cur_seqno; }
        unsigned int get_tot_losses() const { return _tot_losses; }

    private:
        void reboot(); ///< completely reset the internal state

        /// roll loss window values if `_cur_seqno + offs` is a window start.
        void maybe_start_window(int offs=0);

        std::bitset<PACKET_LOST_AFTER> _received_ahead;
        uint32_t _cur_seqno;
        unsigned int _tot_losses;
        unsigned int _last_window_losses, _win_start_losses;
};

/** Round-trip time logger. All timestamps/delays are in microseconds. */
class RTTLogger {
    public:
        RTTLogger();
        uint32_t avg_rtt() const { return _avg_rtt; }
        uint32_t cur_rtt() const { return _cur_rtt; }
        std::chrono::steady_clock::time_point get_last_update() const {
            return _last_update;
        }

        /** Checks whether an update is due.
         * If soon is true, divides the inter-update delay by 2.
         */
        bool update_due(bool soon=false) const;

        void log(const VpnTlvRTTA& rtt_answer);

    private:
        uint32_t _avg_rtt, _cur_rtt;
        static const double EXP_AVG_FACTOR;

        unsigned int _update_delay; // in ms
        static const unsigned int BASE_UPDATE_DELAY; // in ms
        std::chrono::steady_clock::time_point _last_update;
};

class VpnPeer {
    public:
        class NetError : public MsgException {
            public:
                NetError(
                        const std::string& msg,
                        int code=0,
                        bool is_perror=false)
                    : MsgException(msg, code, is_perror) {}
        };

        /// Logs the loss reports sent by the remote peer
        struct LossReports {
            uint32_t prev_seqno, last_seqno;
            uint32_t prev_losses, last_losses;

            double loss_rate() const {
                return (double)(last_losses - prev_losses)
                    / (double)(last_seqno - prev_seqno);
            }
        };

        VpnPeer(UdpVpn* vpn, const sockaddr_in6& ext_addr,
                const in6_addr& int_addr);

        const sockaddr_in6& get_ext_addr() const { return _ext_addr; }
        const in6_addr& get_int_addr() const { return _int_addr; }

        void set_int_addr(const in6_addr& int_addr);

        const PacketLossLogger& get_loss_logger() const { return _packet_loss; }
        const RTTLogger& get_rtt() const { return _rtt; }
        const LossReports& get_loss_reports() const { return _loss_reports; }
        const CongestionController& get_congestion_controller() const {
            return _congestion_controller; }

        void tick(); ///< periodic actions, triggered every UdpVpn tick

        void log_rtta(const VpnTlvRTTA& rtta) { _rtt.log(rtta); }
        void log_loss_report(const VpnTlvLossReport& loss_rep);

        size_t write(const char* data, size_t len);
        size_t write(const VpnPacket& packet);

        uint32_t peek_next_seqno() const { return _next_send_seqno; }
        uint32_t next_seqno() { return _next_send_seqno++; }

        uint64_t get_tot_bytes_sent() const { return _tot_bytes_sent; }
        double get_outbound_byte_rate() const { return _outbound_byte_rate; }

        void got_inbound_packet(const VpnPacket& packet);

        /* === Control protocol === */
        /// Send a control packet if there is data to be sent
        bool send_control_packet();

        /// Append a RTTA for the given RTTQ to the next control packet
        void make_rtta_for(const VpnTlvRTTQ& rttq);

    private: // meth
        void make_loss_report(); ///< Add a loss report to the next control packet
        void cycle_next_control(); ///< Generate a fresh next control packet

    private:
        UdpVpn* _vpn;
        sockaddr_in6 _ext_addr;
        in6_addr _int_addr;
        uint32_t _next_send_seqno;

        uint64_t _tot_bytes_sent, _prev_tot_bytes_sent;
        double _outbound_byte_rate;

        std::chrono::steady_clock::time_point _prev_tick_time;

        PacketLossLogger _packet_loss;
        LossReports _loss_reports;
        RTTLogger _rtt;
        CongestionController _congestion_controller;

        std::unique_ptr<VpnControlPacket> _next_control_packet;
};