import { readFileSync, statSync } from "node:fs";
import { createSecureServer, constants as httpConstants } from "node:http2";
import path from "node:path";

const port = process.env.PORT ?? process.argv[2] ?? 8433;
const serverRoot = process.env.SERVER_ROOT ?? "./app";
const keyPath = process.env.KEY_PATH ?? "./server.key";
const certPath = process.env.CERT_PATH ?? "./server.pem";
const hstsMaxAge = process.env.HSTS_MAX_AGE ?? "31536000";
const corsOrigin = process.env.CORS_ORIGIN ?? "*";

const mimeType = {
	".css": "text/css",
	".doc": "application/msword",
	".eot": "application/vnd.ms-fontobject",
	".html": "text/html",
	".ico": "image/x-icon",
	".jpg": "image/jpeg",
	".js": "text/javascript",
	".json": "application/json",
	".mp3": "audio/mpeg",
	".pdf": "application/pdf",
	".png": "image/png",
	".svg": "image/svg+xml",
	".ttf": "application/x-font-ttf",
	".wav": "audio/wav",
	".zip": "application/zip",
};

const {
	HTTP2_HEADER_PATH: HEADER_PATH,
	HTTP2_HEADER_METHOD: HEADER_METHOD,
	HTTP_STATUS_NOT_FOUND: STATUS_NOT_FOUND,
	HTTP_STATUS_INTERNAL_SERVER_ERROR: STATUS_SERVER_ERROR,
} = httpConstants;

const HEADER_ORIGIN = "origin";

/**
 * HTTP/2 secure server instance
 * @type {import('node:http2').Http2SecureServer}
 */
let server;
try {
	server = createSecureServer({
		cert: readFileSync(certPath),
		key: readFileSync(keyPath),
	});
} catch (error) {
	if (error && "code" in error && error.code === "ENOENT") {
		console.error(`Certificate error: Could not find key or cert files at ${keyPath}, ${certPath}`);
		console.error("Please set KEY_PATH and CERT_PATH environment variables");
		process.exit(1);
	}
	throw error;
}

/**
 * Handles stream errors and sends appropriate HTTP responses
 * @param {unknown} err - The error object
 * @param {import('node:http2').ServerHttp2Stream} stream - The HTTP/2 stream to respond on
 * @param {string | undefined} origin - The request origin for CORS headers
 */
const handleStreamError = (err, stream, origin) => {
	console.error("Stream error:", err);
	let status = STATUS_SERVER_ERROR;
	if (err && "code" in err && typeof err.code === "string") {
		status = err.code === "ENOENT" ? STATUS_NOT_FOUND : STATUS_SERVER_ERROR;
	}
	const body = status === STATUS_NOT_FOUND ? "Not Found" : "Internal Server Error";
	stream.respond({
		":status": status,
		...getResponseHeaders("text/plain", origin),
		"content-length": body.length.toString(),
	});
	stream.end(body);
};

/**
 * Generates common response headers including HSTS and CORS
 * @param {string} mimeType - The MIME type for content-type header
 * @param {string|undefined} ro - The Origin header from the request
 * @returns {Object.<string, string>} Object containing response headers
 */
const getResponseHeaders = (mimeType, ro) => {
	let acao = "*";
	if (corsOrigin !== "*") {
		const allowed = corsOrigin.split(",").map((s) => s.trim());
		acao = ro && allowed.includes(ro) ? ro : allowed[0] || "";
	}
	return {
		"access-control-allow-credentials": "true",
		"access-control-allow-headers": "Content-Type, Authorization",
		"access-control-allow-methods": "GET, HEAD, OPTIONS",
		"access-control-allow-origin": acao,
		"content-type": mimeType,
		"strict-transport-security": `max-age=${hstsMaxAge}; includeSubDomains`,
	};
};

/**
 * Handles incoming HTTP/2 streams
 * @param {import('node:http2').ServerHttp2Stream} stream - The HTTP/2 stream
 * @param {import('node:http2').IncomingHttpHeaders} headers - Request headers
 * @param {number} flags - Stream flags
 */
server.on("stream", (stream, headers) => {
	const reqPath = headers[HEADER_PATH] || "/";
	const reqMethod = headers[HEADER_METHOD] || "GET";
	const requestOrigin =
		typeof headers[HEADER_ORIGIN] === "string" ? headers[HEADER_ORIGIN] : undefined;

	// Handle CORS preflight requests
	if (reqMethod === "OPTIONS") {
		stream.respond({
			":status": 204,
			...getResponseHeaders("text/plain", requestOrigin),
			"content-length": "0",
		});
		stream.end();
		return;
	}

	// Only allow GET and HEAD methods
	if (!["GET", "HEAD"].includes(reqMethod)) {
		stream.respond({
			":status": 405,
			allow: "GET, HEAD, OPTIONS",
			...getResponseHeaders("text/plain", requestOrigin),
		});
		stream.end("Method Not Allowed");
		return;
	}

	let fullPath = path.join(serverRoot, reqPath);

	try {
		const stats = statSync(fullPath);
		if (stats.isDirectory()) {
			fullPath = path.join(fullPath, "index.html");
		}
	} catch (error) {
		handleStreamError(error, stream, requestOrigin);
		return;
	}

	const ext = path.extname(fullPath);
	const responseMimeType = mimeType[ext] || "text/plain";

	stream.respondWithFile(
		fullPath,
		{ ...getResponseHeaders(responseMimeType, requestOrigin) },
		{ onError: (err) => handleStreamError(err, stream, requestOrigin) },
	);
});

/**
 * Handles graceful shutdown of the server
 * @param {string} signal - The signal that triggered shutdown (SIGTERM, SIGINT, etc.)
 */
const gracefulShutdown = (signal) => {
	console.log(`\nReceived ${signal}, shutting down gracefully...`);

	server.close((err) => {
		if (err) {
			console.error("Error during server shutdown:", err);
			process.exit(1);
		}
		console.log("Server closed successfully");
		process.exit(0);
	});

	// Force close after 10 seconds
	setTimeout(() => {
		console.error("Forcing server closure after timeout");
		process.exit(1);
	}, 2000);
};

process.on("SIGTERM", () => gracefulShutdown("SIGTERM"));
process.on("SIGINT", () => gracefulShutdown("SIGINT"));

/**
 * Handles uncaught exceptions
 * @param {Error} error - The uncaught error
 */
process.on("uncaughtException", (error) => {
	console.error("Uncaught Exception:", error);
	gracefulShutdown("uncaughtException");
});

/**
 * Handles unhandled promise rejections
 * @param {any} reason - The rejection reason
 * @param {Promise<unknown>} promise - The promise that was rejected
 */
process.on("unhandledRejection", (reason, promise) => {
	console.error("Unhandled Rejection at:", promise, "reason:", reason);
	gracefulShutdown("unhandledRejection");
});

/**
 * Starts the HTTP/2 server and begins listening for connections
 */
server.listen(parseInt(port, 10), "localhost", () => {
	console.log(`
Server running on https://localhost:${port}
Environment: ${process.env.NODE_ENV || "development"}
Server root: ${serverRoot}
CORS origin: ${corsOrigin}
HSTS max-age: ${hstsMaxAge}
  `);
});