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package com.cunningdj.grokJava;

import java.time.Duration;

import java.time.LocalDateTime;

import java.time.Month;

import java.util.HashMap;

import java.util.LinkedList;

/*

* RATE LIMITER - SLIDING WINDOW PER-USER ALGORITHM

*/

class RateLimiter {

// user ID : queue of request DTs (phased out of window as-you-go)

private HashMap<String, LinkedList<LocalDateTime>> dtQueue;

public final int MAX_REQS_PER_MINUTE;

// FOR TESTING ONLY (otherwise null)

private final LocalDateTime CURRENT_DT_OVERRIDE;

public RateLimiter(int maxReqsPerMinute) {

this.dtQueue = new HashMap<>();

this.MAX_REQS_PER_MINUTE = maxReqsPerMinute;

this.CURRENT_DT_OVERRIDE = null;

}

// MAIN

public static void main(String[] args) {

Tester tester = new Tester();

String testTitle="";

// TEST CLASS METHODS HERE USING TESTER CLASS

testTitle = "RATE_LIMITER";

String TEST_USER = "El Duderino";

String OTHER_TEST_USER = "Mr. Lebowski";

RateLimiter rl = new RateLimiter(3);

tester.isTrue(rl.newRequest(new Request(TEST_USER, RateLimiter.makeTestTime(10, 0))), testTitle);

tester.isTrue(rl.newRequest(new Request(TEST_USER, RateLimiter.makeTestTime(10, 20))), testTitle);

tester.isTrue(rl.newRequest(new Request(TEST_USER, RateLimiter.makeTestTime(10, 40))), testTitle);

// False, and doesn't add it to the queue

tester.isFalse(rl.newRequest(new Request(TEST_USER, RateLimiter.makeTestTime(10, 59))), testTitle);

// Different user; shouldn't fail

tester.isTrue(rl.newRequest(new Request(OTHER_TEST_USER, RateLimiter.makeTestTime(10, 59))), testTitle);

// True; Skipoed the 10:59 request, and 10:00 request is now > 60s old, leaving 2 within the window during check

tester.isTrue(rl.newRequest(new Request(TEST_USER, RateLimiter.makeTestTime(11, 01))), testTitle);

}

// PUBLIC

public boolean newRequest(Request req) {

if (dtQueue.containsKey(req.user)) {

if (dtQueue.get(req.user).size() == MAX_REQS_PER_MINUTE) {

while (dtQueue.get(req.user).size() > 0

&& Duration.between(dtQueue.get(req.user).peek(), req.dt).toMinutes() > 0) {

dtQueue.get(req.user).poll();

}

}

} else {

LinkedList<LocalDateTime> userRequestQ = new LinkedList<>();

dtQueue.put(req.user, userRequestQ);

}

if (dtQueue.get(req.user).size() < MAX_REQS_PER_MINUTE) {

dtQueue.get(req.user).add(req.dt);

return true;

} else {

return false;

}

}

// PRIVATE

// TEST ONLY

private static LocalDateTime makeTestTime(int minutes, int seconds) {

return LocalDateTime.of(2022, Month.MAY, 10, 10, minutes, seconds);

}

// Request

static class Request {

public LocalDateTime dt;

public String user;

public Request(String user) {

this.user = user;

this.dt = LocalDateTime.now();

}

// TESTING ONLY

private Request(String user, LocalDateTime dt) {

this.user = user;

this.dt = dt;

}

}

}