/**
 * WordPress dependencies
 */
import apiFetch from '@safe-wordpress/api-fetch';
import { dispatch, select } from '@safe-wordpress/data';
import { addQueryArgs } from '@safe-wordpress/url';

/**
 * External dependencies
 */
import { logError } from '@nelio-content/utils';
import type { Author, AuthorId } from '@nelio-content/types';

/**
 * Internal dependencies
 */
import { store as NC_DATA } from '../../../store';

export async function loadAuthors(
	authorIds: ReadonlyArray< AuthorId >
): Promise< void > {
	const ids = unique( authorIds ).filter(
		( authorId ) => ! select( NC_DATA ).hasAuthor( authorId )
	);
	ids.forEach( ( id ) => pendingAuthorIds.add( id ) );

	if ( ! pendingAuthorIds.size ) {
		return;
	}

	pendingAuthorRequest = pendingAuthorRequest ?? flushPendingAuthorIds();
	await pendingAuthorRequest;
}

async function flushPendingAuthorIds(): Promise< void > {
	try {
		await waitForBatchWindow();

		while ( pendingAuthorIds.size ) {
			const ids = Array.from( pendingAuthorIds ).filter(
				( authorId ) => ! select( NC_DATA ).hasAuthor( authorId )
			);
			pendingAuthorIds.clear();

			if ( ! ids.length ) {
				continue;
			}

			const authors = await apiFetch< ReadonlyArray< Author > >( {
				path: addQueryArgs( '/nelio-content/v1/author/batch', {
					ids: ids.join( ',' ),
				} ),
			} );
			await dispatch( NC_DATA ).receiveAuthors( authors );
		}
	} catch ( e ) {
		logError( e );
	} finally {
		pendingAuthorRequest = undefined;
	}
}

const unique = < T >( values: ReadonlyArray< T > ): ReadonlyArray< T > =>
	Array.from( new Set( values ) );

const waitForBatchWindow = () =>
	new Promise< void >( ( resolve ) => setTimeout( resolve, 50 ) );

const pendingAuthorIds = new Set< AuthorId >();
let pendingAuthorRequest: Promise< void > | undefined;