import type { Book, BookShelf } from '#lib/content';

export interface BookSeriesGroup {
	name: string;
	url: string;
	books: Book[];
	counts: Record<BookShelf, number>;
}

export interface GroupedBooks {
	series: BookSeriesGroup[];
	standalone: Book[];
}

const positionGroups = { single: 0, range: 1, none: 2 };

function seriesOrder(first: Book, second: Book): number {
	const [firstGroup, firstNumber] = positionKey(first);
	const [secondGroup, secondNumber] = positionKey(second);
	return firstGroup - secondGroup || firstNumber - secondNumber;
}

function positionKey(book: Book): [number, number] {
	const position = book.series?.position ?? '';
	const match = position.match(/\d+(?:\.\d+)?/);
	if (!match) return [positionGroups.none, 0];
	const isRange = /\d\s*[-–]\s*\d/.test(position);
	return [isRange ? positionGroups.range : positionGroups.single, Number(match[0])];
}

function shelfCounts(books: Book[]): Record<BookShelf, number> {
	return {
		read: books.filter((book) => book.shelf === 'read').length,
		reading: books.filter((book) => book.shelf === 'reading').length,
		'want-to-read': books.filter((book) => book.shelf === 'want-to-read').length
	};
}

export function groupBySeries(books: Book[]): GroupedBooks {
	const groups = new Map<string, Book[]>();
	const standalone: Book[] = [];

	for (const book of books) {
		if (!book.series) {
			standalone.push(book);
			continue;
		}
		const key = book.series.url || book.series.name;
		groups.set(key, [...(groups.get(key) ?? []), book]);
	}

	const series = [...groups.values()]
		.map((seriesBooks) => {
			const ordered = [...seriesBooks].sort(seriesOrder);
			return { name: ordered[0].series!.name, url: ordered[0].series!.url, books: ordered, counts: shelfCounts(ordered) };
		})
		.sort((first, second) => second.counts.read - first.counts.read || first.name.localeCompare(second.name));

	return { series, standalone };
}