import MarkdownIt from "markdown-it";
import { type Html, trusted } from "./html.ts";
import { pathUrl } from "./layout.ts";

/**
 * Where a Markdown file lives, so its relative links and images can point at the repo's raw files.
 * `own` marks the operator's words, whose `/static/assets/media/` uploads stay as written.
 */
export type MarkdownBase = { repo: string; dir: string; at: string | null; own?: boolean };

const MEDIA_PREFIX = "/static/assets/media/";
const VIDEO = /\.(mp4|webm)$/i;
const WIDTHS = [25, 33, 50, 66, 75, 100];
const OPTION = /^(width=\d{1,3}|left|center|right|loop)$/;

const SCHEME = /^([a-z][a-z0-9+.-]*):/i;
const ALLOWED_SCHEMES = ["http", "https", "mailto"];

// §25: raw HTML is off, so markdown-it's own escaping is the whole sanitizer.
const md = new MarkdownIt({ html: false, linkify: true });
md.validateLink = (url) => {
	const scheme = SCHEME.exec(url.trim());
	return !scheme || ALLOWED_SCHEMES.includes((scheme[1] as string).toLowerCase());
};
md.core.ruler.push("kepr_raw_links", (state) => {
	const base = state.env as MarkdownBase;
	// Kepr's own pages (docs, support) have no repo, so their links stay as written.
	if (!base.repo) return;
	const visit = (tokens: typeof state.tokens) => {
		for (const token of tokens) {
			const attr = token.type === "link_open" ? "href" : token.type === "image" ? "src" : null;
			const url = attr && token.attrGet(attr);
			if (attr && typeof url === "string") token.attrSet(attr, rawUrl(url, base));
			if (token.children) visit(token.children);
		}
	};
	visit(state.tokens);
});

function rawUrl(url: string, base: MarkdownBase): string {
	if (SCHEME.test(url) || url.startsWith("#") || url.startsWith("//")) return url;
	if (base.own && url.startsWith(MEDIA_PREFIX)) return url;
	// A leading `/` means the repo root, as it does on a code host.
	const resolved = new URL(url, `http://repo/${base.dir ? `${pathUrl(base.dir)}/` : ""}`);
	const at = base.at ? `?at=${base.at}` : "";
	return `/${base.repo}/raw${resolved.pathname}${at}${resolved.hash}`;
}

// A title made only of options sizes and places a picture or video: `![demo](x.mp4 "width=50
// left loop")`. They become classes, since the page's policy allows no inline style. A video
// plays with controls, or, with `loop`, silently on repeat like a GIF.
const image = md.renderer.rules.image;
md.renderer.rules.image = (tokens, idx, options, env, self) => {
	const token = tokens[idx] as (typeof tokens)[number];
	const words = String(token.attrGet("title") ?? "")
		.split(/\s+/)
		.filter(Boolean);
	const styled = words.length > 0 && words.every((word) => OPTION.test(word));
	const src = String(token.attrGet("src") ?? "");
	const video = VIDEO.test(src.split(/[?#]/)[0] as string);
	if (!styled && !video) return image ? image(tokens, idx, options, env, self) : "";
	const asked = Number(words.find((word) => word.startsWith("width="))?.slice(6) ?? 100);
	const width = WIDTHS.find((w) => w >= asked) ?? 100;
	const align = words.find((word) => /^(left|center|right)$/.test(word)) ?? "center";
	const classes = `media media-w${width} media-${align}`;
	if (!video) {
		token.attrs = (token.attrs ?? []).filter(([name]) => name !== "title");
		token.attrSet("class", classes);
		return image ? image(tokens, idx, options, env, self) : "";
	}
	const alt = md.utils.escapeHtml(token.content);
	const play = words.includes("loop")
		? "autoplay muted loop playsinline"
		: 'controls preload="metadata"';
	return `<video class="${classes}" src="${md.utils.escapeHtml(src)}" ${play} aria-label="${alt}"></video>`;
};

export function renderMarkdown(source: string, base: MarkdownBase): Html {
	return trusted(md.render(source, base));
}

/** One of Kepr's own Markdown pages, such as the docs (§21.10), with an anchor on each section. */
export function renderSiteMarkdown(source: string): {
	html: Html;
	sections: { id: string; title: string }[];
} {
	const tokens = md.parse(source, {});
	const sections = tokens.flatMap((token, i) => {
		if (token.type !== "heading_open" || token.tag !== "h2") return [];
		const title = tokens[i + 1]?.content ?? "";
		const id = title.toLowerCase().replace(/[^a-z0-9]+/g, "-");
		token.attrSet("id", id);
		return [{ id, title }];
	});
	return { html: trusted(md.renderer.render(tokens, md.options, {})), sections };
}

/**
 * A paragraph of Markdown source (the README's first paragraph, found as the Atlas finds it) as
 * inline markup, and as plain text for link previews.
 */
export function renderParagraph(source: string, base: MarkdownBase): { html: Html; text: string } {
	const children = md.parseInline(source, base)[0]?.children ?? [];
	const text = children
		.map((token) =>
			token.type === "text" || token.type === "code_inline"
				? token.content
				: token.type === "softbreak"
					? " "
					: "",
		)
		.join("");
	return { html: trusted(md.renderer.renderInline(children, md.options, base)), text };
}

/** One line of Markdown with links and images flattened away, for a row that is itself a link. */
export function renderLine(source: string, base: MarkdownBase): Html {
	const tokens = md.parseInline(source, base)[0]?.children ?? [];
	const kept = tokens.filter((token) => !/^(link_open|link_close|image)$/.test(token.type));
	return trusted(md.renderer.renderInline(kept, md.options, base));
}