Build a simple but effective API rate limiter using plain PHP.

<blockquote><b>Scenario:</b><b></b></blockquote>
<blockquote>You’re building a small SaaS or public API and want to prevent abuse.</blockquote>
<blockquote><b>Requirements:</b><b></b></blockquote>
<ul>
<li>
<blockquote>Limit requests per IP (e.g. 100 requests per hour)</blockquote>
</li>
<li>
<blockquote>Return proper HTTP status codes (429, etc.)</blockquote>
</li>
<li>
<blockquote>Track requests using:</blockquote>
<ul>
<li>
<blockquote>Either files or MySQL (choose one and explain why)</blockquote>
</li>
</ul>
</li>
<li>
<blockquote>Include a reset window</blockquote>
</li>
</ul>
<blockquote><b>Deliverables:</b><b></b></blockquote>
<ul>
<li>
<blockquote>PHP code</blockquote>
</li>
<li>
<blockquote>Clear explanation of the logic</blockquote>
</li>
<li>
<blockquote>One improvement idea for scaling later</blockquote>
</li>
</ul>
<blockquote>Do not use frameworks or external libraries.</blockquote>