import { browser } from "$app/environment";
import { isMarkdownFile } from "$lib/markup/format";
import type { MarkupContext } from "$lib/markup/paths";

// hydration re-runs every load, so the browser hands back the server's render
// instead of loading the markdown pipeline again

const MARKUP_KEY = "data-markup-key";

// the key is only compared against markup already on this page, so stable and
// short is enough, not cryptographic
const digest = (value: string): string => {
	let hash = 5381;
	for (let i = 0; i < value.length; i += 1) hash = (hash * 33) ^ value.charCodeAt(i);
	return (hash >>> 0).toString(36);
};

const keyOf = (filename: string, contents: string, ctx: MarkupContext): string =>
	[
		digest(
			[
				ctx.host ?? "",
				ctx.repo,
				ctx.ref,
				ctx.dir ?? "",
				String(!!ctx.sourceLines),
				filename
			].join("\n")
		),
		contents.length.toString(36),
		digest(contents)
	].join(".");

const mark = (key: string, html: string): string => `<div ${MARKUP_KEY}="${key}">${html}</div>`;

// reads back a render this module wrote for the same contents and context
const rendered = (key: string): string | null => {
	if (!browser) return null;
	const node = document.querySelector(`[${MARKUP_KEY}="${key}"]`);
	return node instanceof HTMLElement ? node.innerHTML : null;
};

const render = async (
	key: string,
	contents: string,
	ctx: MarkupContext
): Promise<string | null> => {
	const reused = rendered(key);
	if (reused !== null) return mark(key, reused);

	const { SOURCE_LIMIT, renderMarkdown } = await import("./markdown");
	if (contents.length > SOURCE_LIMIT) return null;
	const html = await renderMarkdown(contents, ctx);
	return html === null ? null : mark(key, html);
};

export const renderDocument = async (
	filename: string,
	contents: string,
	ctx: MarkupContext
): Promise<string | null> =>
	isMarkdownFile(filename) ? render(keyOf(filename, contents, ctx), contents, ctx) : null;

// like renderDocument, but for content that is always markdown (issue and
// comment bodies) rather than a repo file with an extension to sniff
export const renderMarkup = (contents: string, ctx: MarkupContext): Promise<string | null> =>
	render(keyOf("", contents, ctx), contents, ctx);