/*
 * IptController.h — Inter-Packet Timing obfuscation for tgnet
 * Ported from telemt/tdlib-obf (MIT License, Copyright 2026 telemt community)
 * Adapted for tgnet: C++17, no tdlib dependencies.
 *
 * IPT uses a two-state Markov model (Burst / Idle) to add randomised delays
 * between TLS records, mimicking the inter-packet timing of interactive
 * browser sessions and defeating timing-based DPI correlation attacks.
 *
 * Burst state: lognormal delays (µ=3.5ms, σ=0.8), capped at 200ms
 * Idle  state: heavy-tail Pareto gaps (α=1.5, scale=500ms, max=3s)
 *
 * Bypass (zero delay) for: BulkData, Keepalive, AuthHandshake
 */

#ifndef IPT_CONTROLLER_H
#define IPT_CONTROLLER_H

#include <cstdint>
#include "DrsEngine.h"  // for TrafficHint

namespace stealth {

struct IptParams {
    double burst_mu_ms{3.5};
    double burst_sigma{0.8};
    double burst_max_ms{200.0};

    double idle_alpha{1.5};
    double idle_scale_ms{500.0};
    double idle_max_ms{3000.0};

    // Markov transition probabilities
    double p_burst_stay{0.95};    // P(stay Burst | was Burst)
    double p_idle_to_burst{0.30}; // P(go Burst  | was Idle)
};

class IptController {
public:
    explicit IptController(const IptParams &params = IptParams{});

    // Returns delay in microseconds before the next record should be sent.
    // has_pending_data: true if outgoing buffer is non-empty after this send.
    // hint: traffic type — BulkData/Keepalive/AuthHandshake bypass IPT (return 0).
    uint64_t next_delay_us(bool has_pending_data,
                           TrafficHint hint = TrafficHint::Interactive);

    // Sample an idle gap delay — used by ChaffScheduler.
    uint64_t sample_idle_delay_us();

private:
    enum class State : uint8_t { Idle = 0, Burst = 1 };

    static bool is_bypass(TrafficHint hint);
    State transition(bool has_pending_data);

    double sample_uniform01();
    double sample_normal();
    double sample_lognormal(double mu, double sigma);
    double sample_pareto(double u, double alpha, double scale, double max_val) const;

    IptParams params_;
    State state_{State::Idle};
    bool has_spare_normal_{false};
    double spare_normal_{0.0};
};

}  // namespace stealth

#endif  // IPT_CONTROLLER_H