LootLockerRateLimiter.h

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// Copyright (c) 2021 LootLocker
 
#pragma once
 
#include "CoreMinimal.h"

class LOOTLOCKERSDK_API FLootLockerRateLimiter
{
public:
    // -------------------------------------------------------------------------
    // Algorithm constants (all match the Unity SDK values)
    // -------------------------------------------------------------------------

    static constexpr int32 TripWireTimeFrameSeconds = 60;

    static constexpr int32 MaxRequestsPerTripWireTimeFrame = 280;

    static constexpr int32 SecondsPerBucket = 5;

    static constexpr float AllowXPercentOfTripWireMaxForMovingAverage = 0.8f;

    static constexpr int32 CountMovingAverageAcrossNTripWireTimeFrames = 3;
 
    // -------------------------------------------------------------------------
    // Derived constants
    // -------------------------------------------------------------------------

    static constexpr int32 BucketsPerTimeFrame = TripWireTimeFrameSeconds / SecondsPerBucket;

    static constexpr int32 RateLimitMovingAverageBucketCount = CountMovingAverageAcrossNTripWireTimeFrames * BucketsPerTimeFrame;

    static constexpr int32 MaxRequestsPerBucketOnMovingAverage =
        (MaxRequestsPerTripWireTimeFrame * 4) / (BucketsPerTimeFrame * 5);
 
    // -------------------------------------------------------------------------
    // Lifecycle
    // -------------------------------------------------------------------------
 
    FLootLockerRateLimiter();
    virtual ~FLootLockerRateLimiter() = default;

    void Reset();
 
    // -------------------------------------------------------------------------
    // Public API
    // -------------------------------------------------------------------------

    virtual bool AddRequestAndCheckIfRateLimitHit();

    int32 GetSecondsLeftOfRateLimit() const;
 
protected:
    // -------------------------------------------------------------------------
    // Testability hook
    // -------------------------------------------------------------------------

    virtual FDateTime GetTimeNow() const;
 
    // -------------------------------------------------------------------------
    // State (protected for test-subclass access)
    // -------------------------------------------------------------------------

    bool bEnableRateLimiter = true;

    bool bFirstRequestSent = false;

    int32 Buckets[RateLimitMovingAverageBucketCount];

    int32 LastBucket = -1;

    FDateTime LastBucketChangeTime;

    int32 TotalRequestsInBuckets = 0;

    int32 TotalRequestsInBucketsInTripWireTimeFrame = 0;

    bool bIsRateLimited = false;

    FDateTime RateLimitResolvesAt;
 
private:
    int32 MoveCurrentBucket(const FDateTime& Now);
};