/**
 * Default handler for returning HTML with SSI support
 * @module
 */

import * as fs from "@std/fs";
import * as path from "@std/path";
import { md_to_html } from "./markdown.ts";

// https://stackoverflow.com/a/75205316
const replaceAsync = async (
	str: string,
	regex: RegExp,
	asyncFn: (match: any, ...args: any) => Promise<any>,
) => {
	const promises: Promise<any>[] = [];
	str.replace(regex, (match, ...args) => {
		promises.push(asyncFn(match, ...args));
		return match;
	});
	const data = await Promise.all(promises);
	return str.replace(regex, () => data.shift());
};

export async function load_html_with_ssi(html_file: string): Promise<string> {
	const directory = path.dirname(html_file);
	const html_file_content: string = await Deno.readTextFile(html_file);
	const processed: string = await replaceAsync(
		html_file_content,
		/\<\!--\s+#include\s+(?<directive>.*?)\s*-->/gm,
		async (_match, directive, index): Promise<string | undefined> => {
			const file_include_options = Array.from(
				directive.matchAll(/(?<option>(?<op>or)?\s*["'](?<location>[^"']*?)['"])+/gm),
			).map((match) => match?.groups?.location);

			let include_location;
			for (const location of file_include_options) {
				const resolved = path.resolve(path.join(directory, location));
				if (!resolved.startsWith(Deno.cwd())) {
					console.error(
						`Cannot include files above the working directory (${Deno.cwd()}): ${location} ${html_file}:${index}`,
					);
					break;
				}

				const exists = await fs.exists(resolved);
				if (!exists) {
					continue;
				}

				include_location = resolved;
				break;
			}

			if (!include_location) {
				console.error(
					`Cannot locate any of these files to include: ${file_include_options}`,
				);
				return;
			}

			const HANDLERS: Record<string, (include_path: string) => Promise<string> | string> = {
				default: async (include_path: string) => {
					try {
						return await Deno.readTextFile(include_path);
					} catch (error) {
						console.dir({ error });
						throw error;
					}
				},

				".md": async (include_path: string) => {
					const markdown_content = await Deno.readTextFile(include_path);
					return md_to_html(markdown_content);
				},

				".html": load_html_with_ssi,
			};

			const extension = path.extname(include_location);
			const handler = extension
				? (HANDLERS[extension.toLowerCase()] ?? HANDLERS.default)
				: HANDLERS.default;

			const result = await handler(include_location);
			return result;
		},
	);

	return processed;
}

/**
 * Handles requests for HTML files, processing any server-side includes
 *
 * @param request The incoming HTTP request
 * @returns Either a response (an HTML file was requested and returned properly) or undefined if unhandled.
 */
export default async function handle_html(request: Request): Promise<Response | undefined> {
	const url = new URL(request.url);
	const normalized_path = path.resolve(path.normalize(url.pathname).replace(/^\/+/, ""));
	if (!normalized_path.startsWith(Deno.cwd())) {
		return;
	}

	const initial_extension = path.extname(normalized_path)?.slice(1)?.toLowerCase() ?? "";
	const target_path: string =
		initial_extension.length === 0 ? path.join(normalized_path, "index.html") : normalized_path;
	const extension = path.extname(target_path).slice(1).toLowerCase();

	if (extension !== "html") {
		return;
	}

	try {
		const stat = await Deno.stat(target_path);
		if (!stat.isFile) {
			return;
		}

		const processed: string = await load_html_with_ssi(target_path);

		const accepts: string = request.headers.get("accept") ?? "text/html";
		const headers: Record<string, string> = {};
		switch (accepts) {
			case "text/plain":
				headers["Content-Type"] = "text/plain";
				break;

			case "text/html":
			default:
				headers["Content-Type"] = "text/html";
				break;
		}

		return new Response(processed, {
			headers,
		});
	} catch (error) {
		if (error instanceof Deno.errors.NotFound) {
			return;
		}

		if (error instanceof Deno.errors.PermissionDenied) {
			return new Response("Permission Denied", {
				status: 400,
				headers: {
					"Content-Type": "text/plain",
				},
			});
		}

		throw error;
	}
}