import { Log } from '@servicetitan/log-service';
import { useOptionalDependencies } from '@servicetitan/react-ioc';
import { EXPOSED_DEPENDENCIES_TOKEN, EXPOSED_INSTANCE_DEPENDENCIES_TOKEN } from './common';
import { LoaderProps } from './loader';
import { getBundleInfo, supportsPrefetch } from './utils';

/**
 * Prefetch and cache bundle info for a given MFE, so that Loader can load it faster later.
 * @param src - The main package URL for the MFE
 * @returns Promise resolving to the BundleInfo
 */
export function usePrefetch() {
    const [logService, exposedDependencies = EXPOSED_DEPENDENCIES] = useOptionalDependencies(
        Log,
        EXPOSED_DEPENDENCIES_TOKEN
    );
    const [exposedInstanceDependencies = EXPOSED_INSTANCE_DEPENDENCIES] = useOptionalDependencies(
        EXPOSED_INSTANCE_DEPENDENCIES_TOKEN
    );
    const prefetch = async (src: string, { cache = -1 }: Pick<LoaderProps<any>, 'cache'> = {}) => {
        try {
            const bundleInfo = await getBundleInfo({
                exposedDependencies,
                exposedInstanceDependencies,
                mainPackageUrl: src,
                cache,
                retries: 0,
            });

            if (bundleInfo.cacheHit) {
                return;
            }

            const { css, js } = bundleInfo.urls;
            if (supportsPrefetch()) {
                addLinks([
                    ...css.map(href => ({ href, as: 'style' })),
                    ...js.map(href => ({ href, as: 'script' })),
                ]);
            } else {
                await Promise.all([...css, ...js].map(url => fetch(url, { priority: 'low' })));
            }
        } catch (e: any) {
            logService?.warning({
                category: 'Microfrontends.Prefetch',
                message: `Failed to prefetch ${src}`,
                data: e,
            });
        }
    };

    return { prefetch };
}

interface Link {
    as: string;
    href: string;
}

function addLinks(links: Link[]) {
    const existingLinks = document.head.getElementsByTagName('link');
    const existingHrefs = new Set(Array.from(existingLinks).map(({ href }) => href));

    links.forEach(({ as, href }) => {
        if (!existingHrefs.has(href)) {
            const link = document.createElement('link');
            link.as = as;
            link.crossOrigin = 'anonymous';
            link.href = href;
            link.rel = 'prefetch';
            document.head.append(link);
        }
    });
}