import crypto from 'node:crypto';
import express, { type Request, type Response } from 'express';
import { StreamableHTTPServerTransport } from '@modelcontextprotocol/sdk/server/streamableHttp.js';
import { isInitializeRequest } from '@modelcontextprotocol/sdk/types.js';
import type { Config } from '../config.ts';
import { createServer } from '../mcp/server.ts';
import type { Services } from '../services.ts';
import { createApiRouter } from './api.ts';
import { createAppRouter } from './app-page.ts';
import { bearerAuth, pathSecret } from './auth.ts';
import { tokenPage, tokenScript } from './token-page.ts';

/**
 * Streamable-HTTP front end, for use as a remote MCP connector.
 *
 * Sessions are stateful: a client POSTs `initialize`, gets an
 * `Mcp-Session-Id` back, and reuses it for subsequent POSTs, an optional GET
 * (the SSE channel for server-initiated messages), and a DELETE to close.
 * Each session owns one McpServer instance, which keeps per-session caches
 * (the `/me` lookup) from leaking between callers.
 */

const MCP_PATH = '/mcp';
/** The CLI's surface: file bytes, sync manifest, on-demand re-crawl. */
const API_PATH = '/api';
/** Sessions are dropped after this long without traffic, in case DELETE never arrives. */
const SESSION_IDLE_MS = 30 * 60 * 1000;

interface Session {
	transport: StreamableHTTPServerTransport;
	close: () => Promise<void>;
	lastSeen: number;
}

export function createHttpApp(config: Config, services?: Services): express.Express {
	const app = express();
	app.disable('x-powered-by');
	// Caddy sits in front and terminates TLS; trust its forwarding headers so
	// logged client IPs are real rather than the proxy's.
	app.set('trust proxy', true);

	const sessions = new Map<string, Session>();

	const sweep = setInterval(() => {
		const cutoff = Date.now() - SESSION_IDLE_MS;
		for (const [id, session] of sessions) {
			if (session.lastSeen < cutoff) {
				sessions.delete(id);
				void session.close().catch(() => {});
			}
		}
	}, 60_000);
	sweep.unref();

	// Liveness probe for Docker/Caddy. Deliberately before auth and free of any
	// detail about the instance or the account.
	app.get('/healthz', (_req, res) => {
		res.json({ status: 'ok', sessions: sessions.size, index: services?.store ? 'on' : 'off' });
	});

	// MCP_AUTH_TOKEN opens both surfaces: the MCP endpoint and the CLI's API. The
	// connector token opens /mcp alone. claude.ai stores it as a request header,
	// and a credential held by a third party should reach the read-only tools,
	// not /api, which can replace the Schulcloud token and stream the file mirror.
	// The web app, when a password is configured. Mounted before the token gate
	// so its login screen is reachable without one — it is the thing that issues
	// the session everything else then accepts.
	const appSurface = services ? createAppRouter(config) : undefined;
	if (appSurface) app.use('/app', appSurface.router);

	const loggedIn = appSurface ? (req: Request) => appSurface.auth.verify(req.get('cookie')) : undefined;

	if (config.authToken) {
		app.use(MCP_PATH, bearerAuth(config.connectorToken ? [config.authToken, config.connectorToken] : config.authToken));
		app.use(API_PATH, bearerAuth(config.authToken, loggedIn));
	} else {
		console.warn(
			'[schulcloud-mcp] MCP_AUTH_TOKEN is not set — the endpoint is UNAUTHENTICATED. ' +
				'Only acceptable when bound to localhost or an otherwise private network.',
		);
	}

	if (services) {
		app.use(API_PATH, createApiRouter(services));
		// The page to paste a fresh Schulcloud token into. It holds no secret: what
		// it sends goes to /api/token, behind the bearer check above.
		app.get('/token', tokenPage);
		app.get('/token.js', tokenScript);
	}

	const handlePost = async (req: Request, res: Response): Promise<void> => {
		const sessionId = req.get('mcp-session-id');

		try {
			if (sessionId) {
				const session = sessions.get(sessionId);
				if (!session) {
					res.status(404).json(rpcError(-32001, 'Unknown or expired session. Re-initialize.'));
					return;
				}
				session.lastSeen = Date.now();
				await session.transport.handleRequest(req, res, req.body);
				return;
			}

			if (!isInitializeRequest(req.body)) {
				res.status(400).json(rpcError(-32000, 'Missing Mcp-Session-Id header; send an initialize request first.'));
				return;
			}

			const { server } = createServer(config, services);
			const transport = new StreamableHTTPServerTransport({
				sessionIdGenerator: () => crypto.randomUUID(),
				onsessioninitialized: (id) => {
					sessions.set(id, {
						transport,
						close: async () => {
							await transport.close().catch(() => {});
							await server.close().catch(() => {});
						},
						lastSeen: Date.now(),
					});
					console.log(`[schulcloud-mcp] session ${id} initialized`);
				},
			});

			transport.onclose = () => {
				if (transport.sessionId) {
					sessions.delete(transport.sessionId);
					console.log(`[schulcloud-mcp] session ${transport.sessionId} closed`);
				}
			};

			await server.connect(transport);
			await transport.handleRequest(req, res, req.body);
		} catch (error) {
			console.error('[schulcloud-mcp] POST failed:', error);
			if (!res.headersSent) res.status(500).json(rpcError(-32603, 'Internal server error'));
		}
	};

	app.post(MCP_PATH, express.json({ limit: '4mb' }), handlePost);

	// GET opens the server→client SSE stream; DELETE ends the session.
	const bySession = async (req: Request, res: Response): Promise<void> => {
		const sessionId = req.get('mcp-session-id');
		const session = sessionId ? sessions.get(sessionId) : undefined;
		if (!session) {
			res.status(404).json(rpcError(-32001, 'Unknown or expired session.'));
			return;
		}
		session.lastSeen = Date.now();
		try {
			await session.transport.handleRequest(req, res);
		} catch (error) {
			console.error('[schulcloud-mcp] session request failed:', error);
			if (!res.headersSent) res.status(500).json(rpcError(-32603, 'Internal server error'));
		}
	};

	app.get(MCP_PATH, bySession);
	app.delete(MCP_PATH, bySession);

	// The same endpoint without a bearer token, for clients that cannot send one:
	// claude.ai's connector dialog takes only a URL. The path is the credential
	// here, so nothing in this server logs request paths — keep it that way — and
	// the Caddy snippet redacts it from the access log. A stopgap until the
	// endpoint speaks OAuth, which is what connectors are meant to use.
	if (config.mcpPathSecret) {
		const secretMcpPath = '/:secret/mcp';
		const gate = pathSecret(config.mcpPathSecret);
		app.post(secretMcpPath, gate, express.json({ limit: '4mb' }), handlePost);
		app.get(secretMcpPath, gate, bySession);
		app.delete(secretMcpPath, gate, bySession);
	}

	app.use((_req, res) => res.status(404).json({ error: 'not_found' }));

	return app;
}

function rpcError(code: number, message: string) {
	return { jsonrpc: '2.0' as const, error: { code, message }, id: null };
}