import { mkdir, open, readdir, stat } from "node:fs/promises";
import path from "node:path";

export type AnnotationPageInfo = {
	name: string;
	title: string;
	size: number;
	modifiedAt: string;
	href: string;
};

const annotationPagesRoot = path.resolve(
	process.env.ANNOTATION_PAGES_DIR?.trim() || "/home/mi/annotation-pages",
);

export async function listAnnotationPages(): Promise<AnnotationPageInfo[]> {
	await mkdir(annotationPagesRoot, { recursive: true });
	const entries = await readdir(annotationPagesRoot, { withFileTypes: true });
	const pages = await Promise.all(
		entries
			.filter((entry) => entry.isFile() && isSafeHtmlName(entry.name))
			.map(async (entry) => {
				const filePath = path.join(annotationPagesRoot, entry.name);
				const [fileStat, title] = await Promise.all([
					stat(filePath),
					readHtmlTitle(filePath, entry.name),
				]);
				return {
					name: entry.name,
					title,
					size: fileStat.size,
					modifiedAt: fileStat.mtime.toISOString(),
					href: `/annotations/${encodeURIComponent(entry.name)}`,
				};
			}),
	);

	return pages.sort(
		(left, right) =>
			Date.parse(right.modifiedAt) - Date.parse(left.modifiedAt) ||
			left.name.localeCompare(right.name, "zh-CN"),
	);
}

export function resolveAnnotationPage(name: string): string | null {
	if (!isSafeHtmlName(name)) return null;
	const resolved = path.resolve(annotationPagesRoot, name);
	if (path.dirname(resolved) !== annotationPagesRoot) return null;
	return resolved;
}

function isSafeHtmlName(name: string): boolean {
	return (
		name === path.basename(name) &&
		!name.startsWith(".") &&
		/\.html?$/i.test(name)
	);
}

async function readHtmlTitle(filePath: string, fileName: string) {
	const handle = await open(filePath, "r");
	try {
		const buffer = Buffer.alloc(16 * 1024);
		const { bytesRead } = await handle.read(buffer, 0, buffer.length, 0);
		const head = buffer.subarray(0, bytesRead).toString("utf8");
		const match = head.match(/<title[^>]*>([\s\S]*?)<\/title>/i);
		const title = match?.[1]
			?.replace(/<[^>]+>/g, " ")
			.replace(/\s+/g, " ")
			.trim();
		return title ? decodeHtmlEntities(title) : stripHtmlExtension(fileName);
	} finally {
		await handle.close();
	}
}

function stripHtmlExtension(fileName: string) {
	return fileName.replace(/\.html?$/i, "");
}

function decodeHtmlEntities(value: string) {
	return value
		.replaceAll("&amp;", "&")
		.replaceAll("&lt;", "<")
		.replaceAll("&gt;", ">")
		.replaceAll("&quot;", '"')
		.replaceAll("&#39;", "'");
}