<?php

// First we'll look at basic rate limiting. Suppose
// we want to limit our handling of incoming requests.
// We'll serve these requests from an array.
$requests = [1, 2, 3, 4, 5];

// This $limiter variable will be used to ensure we process
// a request only every 200 milliseconds.
$limiter = microtime(true);

foreach ($requests as $req) {
    // By checking the time before processing each request,
    // we limit ourselves to 1 request every 200 milliseconds.
    while (microtime(true) - $limiter < 0.2) {
        usleep(1000); // Sleep for 1ms to avoid busy waiting
    }
    
    echo "request $req " . date('Y-m-d H:i:s') . PHP_EOL;
    $limiter = microtime(true);
}

// Now let's look at bursty rate limiting. We may want to allow
// short bursts of requests in our rate limiting scheme while
// preserving the overall rate limit.

// This burstyLimiter array will allow bursts of up to 3 events.
$burstyLimiter = [microtime(true), microtime(true), microtime(true)];
$burstyRequests = [1, 2, 3, 4, 5];

foreach ($burstyRequests as $req) {
    // Use the oldest timestamp in the burstyLimiter
    $oldestTime = min($burstyLimiter);
    
    // If the oldest timestamp is less than 200ms ago, we need to wait
    $timeToWait = 0.2 - (microtime(true) - $oldestTime);
    if ($timeToWait > 0) {
        usleep($timeToWait * 1000000);
    }
    
    echo "request $req " . date('Y-m-d H:i:s') . PHP_EOL;
    
    // Update the oldest timestamp with the current time
    $burstyLimiter[array_search($oldestTime, $burstyLimiter)] = microtime(true);
}