import { useEffect } from 'react';
import { getAppConfig } from '@/lib/config';

const SCRIPT_ELEMENT_ID = 'umami-analytics-script';

/**
 * Injects the self-hosted Umami tracking script when both the script URL and the website ID are
 * configured at build time. Renders nothing.
 *
 * A component rather than a tag in index.html, because the website ID is a build-time variable
 * and index.html cannot read import.meta.env. It also makes the "never in development" and "once
 * only" rules testable.
 *
 * `Do Not Track` is deliberately not consulted: Umami sets no cookies and collects no personal
 * data, and this SPA's audience is a known set of operators, so honouring DNT would reduce data
 * without protecting anyone. A conscious choice rather than an omission.
 */
export function UmamiAnalytics() {
    useEffect(() => {
        const { umamiScriptUrl, umamiWebsiteId } = getAppConfig();

        // Never in local development, regardless of configuration, so local testing does not
        // pollute the real visitor analytics.
        if (import.meta.env.DEV || !umamiScriptUrl || !umamiWebsiteId) {
            return;
        }

        if (document.getElementById(SCRIPT_ELEMENT_ID) !== null) {
            return;
        }

        const script = document.createElement('script');
        script.id = SCRIPT_ELEMENT_ID;
        script.src = umamiScriptUrl;
        script.defer = true;
        script.setAttribute('data-website-id', umamiWebsiteId);
        document.head.appendChild(script);

        // Deliberately no cleanup removing the script. Under StrictMode the double-invocation
        // would become inject -> remove -> inject, and removing the element does not unregister
        // the listeners Umami already installed — so the first page view can be counted twice.
        // This component lives for the application's lifetime and has nothing to clean up; the
        // duplicate guard above handles re-invocation on its own.
    }, []);

    return null;
}