import { readFile, stat } from 'node:fs/promises';
import { createServer } from 'node:http';
import path from 'node:path';
import { fileURLToPath } from 'node:url';
import { validateNetworkData } from './src/lib/shared/networkSchemaCore.mjs';
import {
	getWritableState,
	readNetworkFile,
	writeNetworkFile
} from './src/lib/shared/networkPersistenceCore.mjs';

const currentFilePath = fileURLToPath(import.meta.url);
const currentDirPath = path.dirname(currentFilePath);
const buildDir = path.resolve(currentDirPath, 'build');

const HOST = process.env.HOST ?? '0.0.0.0';
const PORT = Number(process.env.PORT ?? 3000);
const MAX_BODY_BYTES = 1024 * 1024;

const contentTypeByExtension = {
	'.html': 'text/html; charset=utf-8',
	'.js': 'text/javascript; charset=utf-8',
	'.css': 'text/css; charset=utf-8',
	'.json': 'application/json; charset=utf-8',
	'.png': 'image/png',
	'.jpg': 'image/jpeg',
	'.jpeg': 'image/jpeg',
	'.svg': 'image/svg+xml; charset=utf-8',
	'.ico': 'image/x-icon',
	'.webp': 'image/webp',
	'.txt': 'text/plain; charset=utf-8'
};

function sendJson(response, status, payload, extraHeaders = {}) {
	const body = JSON.stringify(payload);
	response.writeHead(status, {
		'Content-Type': 'application/json; charset=utf-8',
		'Content-Length': Buffer.byteLength(body),
		'Cache-Control': 'no-store',
		...extraHeaders
	});
	response.end(body);
}

function badRequest(response, message, details) {
	sendJson(response, 400, {
		error: message,
		...(details ? { details } : {})
	});
}

function resolveReadOnlyErrorMessage(reason) {
	if (!reason) {
		return 'Write API unavailable in current deployment.';
	}
	return `Write API unavailable: ${reason}`;
}

async function serveApi(request, response) {
	if (request.method === 'GET') {
		try {
			const [payload, writableState] = await Promise.all([readNetworkFile(), getWritableState()]);
			const validation = validateNetworkData(payload.data);
			if (!validation.valid) {
				sendJson(response, 500, {
					error: 'Stored network data is invalid',
					details: validation.errors
				});
				return;
			}

			sendJson(response, 200, {
				data: validation.data,
				writable: writableState.writable,
				writableReason: writableState.reason,
				source: payload.source,
				updatedAt: payload.updatedAt
			});
		} catch (error) {
			sendJson(response, 500, {
				error: error instanceof Error ? error.message : 'Failed to read network data'
			});
		}
		return;
	}

	if (request.method === 'PUT') {
		const writableStateBeforeWrite = await getWritableState();
		if (!writableStateBeforeWrite.writable) {
			sendJson(response, 403, {
				error: resolveReadOnlyErrorMessage(writableStateBeforeWrite.reason),
				writable: false,
				writableReason: writableStateBeforeWrite.reason
			});
			return;
		}

		let raw = '';
		let accumulatedSize = 0;
		for await (const chunk of request) {
			const chunkSize = Buffer.isBuffer(chunk) ? chunk.length : Buffer.byteLength(chunk);
			accumulatedSize += chunkSize;
			if (accumulatedSize > MAX_BODY_BYTES) {
				raw = '';
				accumulatedSize = 0;
				sendJson(
					response,
					413,
					{ error: `Payload too large. Max body size is ${MAX_BODY_BYTES} bytes.` },
					{ Connection: 'close' }
				);
				request.destroy();
				return;
			}
			raw += typeof chunk === 'string' ? chunk : chunk.toString('utf8');
		}

		let parsed;
		try {
			parsed = JSON.parse(raw);
		} catch {
			badRequest(response, 'Request body must be valid JSON');
			return;
		}

		const validation = validateNetworkData(parsed);
		if (!validation.valid) {
			badRequest(response, 'Network data validation failed', validation.errors);
			return;
		}

		try {
			const metadata = await writeNetworkFile(validation.data);
			const writableStateAfterWrite = await getWritableState();
			sendJson(response, 200, {
				data: validation.data,
				writable: writableStateAfterWrite.writable,
				writableReason: writableStateAfterWrite.reason,
				source: metadata.source,
				updatedAt: metadata.updatedAt
			});
		} catch (error) {
			sendJson(response, 500, {
				error: error instanceof Error ? error.message : 'Failed to persist network data'
			});
		}
		return;
	}

	sendJson(response, 405, { error: 'Method not allowed' });
}

function safeRelativePath(requestPath) {
	const decoded = decodeURIComponent(requestPath);
	const normalized = path.posix.normalize(decoded);
	if (normalized.startsWith('..')) {
		return null;
	}
	return normalized;
}

async function serveStatic(requestPath, response) {
	const relativePath = safeRelativePath(requestPath);
	if (relativePath === null) {
		response.writeHead(400);
		response.end('Bad request');
		return;
	}

	const requestedFilePath = path.join(
		buildDir,
		relativePath === '/' ? 'index.html' : relativePath.slice(1)
	);

	const sendFile = async (filePath) => {
		const ext = path.extname(filePath).toLowerCase();
		const contentType = contentTypeByExtension[ext] ?? 'application/octet-stream';
		const content = await readFile(filePath);
		response.writeHead(200, {
			'Content-Type': contentType,
			'Cache-Control': ext === '.html' ? 'no-store' : 'public, max-age=31536000, immutable'
		});
		response.end(content);
	};

	try {
		const fileInfo = await stat(requestedFilePath);
		if (fileInfo.isDirectory()) {
			await sendFile(path.join(requestedFilePath, 'index.html'));
			return;
		}
		await sendFile(requestedFilePath);
		return;
	} catch {
		// continue with SPA fallback
	}

	try {
		await sendFile(path.join(buildDir, 'index.html'));
	} catch {
		response.writeHead(404);
		response.end('Not found');
	}
}

const server = createServer(async (request, response) => {
	try {
		const requestUrl = new URL(request.url ?? '/', `http://${request.headers.host ?? 'localhost'}`);
		if (requestUrl.pathname === '/api/network-data') {
			await serveApi(request, response);
			return;
		}
		await serveStatic(requestUrl.pathname, response);
	} catch (error) {
		// eslint-disable-next-line no-console
		console.error('[OpenNetworkDiagram] request handling failed', error);
		if (response.headersSent || response.writableEnded) {
			response.destroy();
			return;
		}
		const body = JSON.stringify({ error: 'Internal server error' });
		response.statusCode = 500;
		response.setHeader('Content-Type', 'application/json; charset=utf-8');
		response.setHeader('Content-Length', Buffer.byteLength(body));
		response.setHeader('Cache-Control', 'no-store');
		response.end(body);
	}
});

server.listen(PORT, HOST, () => {
	// eslint-disable-next-line no-console
	console.log(`[OpenNetworkDiagram] listening on http://${HOST}:${PORT}`);
});