import { createServer } from 'node:http';
import { readFileSync, statSync, realpathSync } from 'node:fs';
import { extname, resolve, sep } from 'node:path';
import { fileURLToPath } from 'node:url';

import {
  estimateEntropy,
  generateMemorizable,
  generateRandom,
} from './src/generator.js';
import { listMeta } from './src/words.js';

const PUBLIC_DIR = resolve(fileURLToPath(new URL('./public/', import.meta.url)));
const NOT_FOUND_PAGE = resolve(PUBLIC_DIR, '404.html');
const MAX_BODY_BYTES = 64 * 1024;
const PORT = Number.parseInt(process.env.PORT || '3000', 10);
const HOST = '0.0.0.0';

const SECURITY_HEADERS = {
  'X-Content-Type-Options': 'nosniff',
  'Referrer-Policy': 'no-referrer',
  'X-Frame-Options': 'DENY',
  'Content-Security-Policy': "default-src 'self'; script-src 'self'; style-src 'self'; img-src 'self' data:; connect-src 'self'; base-uri 'none'; form-action 'self'",
};

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

function sendBuffer(req, res, status, body, headers) {
  res.writeHead(status, {
    ...SECURITY_HEADERS,
    'Content-Length': body.length,
    ...headers,
  });
  if (req.method === 'HEAD') {
    res.end();
    return;
  }
  res.end(body);
}

function sendJson(req, res, status, payload) {
  const body = Buffer.from(JSON.stringify(payload));
  sendBuffer(req, res, status, body, {
    'Content-Type': 'application/json; charset=utf-8',
    'Cache-Control': 'no-store',
  });
}

function sendError(req, res, status, message) {
  sendJson(req, res, status, { error: message });
}

function sendNotFoundPage(req, res) {
  let body;
  try {
    body = readFileSync(NOT_FOUND_PAGE);
  } catch {
    body = Buffer.from('<!doctype html><title>Not found</title><h1>Not found</h1>');
  }
  sendBuffer(req, res, 404, body, {
    'Content-Type': 'text/html; charset=utf-8',
    'Cache-Control': 'no-store',
  });
}

function contentTypeFor(filePath) {
  return CONTENT_TYPES[extname(filePath).toLowerCase()] || 'application/octet-stream';
}

function resolveStaticPath(pathname) {
  let decoded;
  try {
    decoded = decodeURIComponent(pathname);
  } catch {
    return null;
  }
  if (decoded.includes('\0')) return null;

  const relative = decoded === '/' ? 'index.html' : decoded.replace(/^\/+/, '');
  const target = resolve(PUBLIC_DIR, relative);
  if (target !== PUBLIC_DIR && !target.startsWith(PUBLIC_DIR + sep)) {
    return null;
  }
  return target;
}

function serveStatic(req, res, pathname) {
  const target = resolveStaticPath(pathname);
  if (!target) {
    sendNotFoundPage(req, res);
    return;
  }

  let stats;
  let real;
  try {
    stats = statSync(target);
    real = realpathSync(target);
  } catch {
    sendNotFoundPage(req, res);
    return;
  }

  if (!stats.isFile() || (real !== PUBLIC_DIR && !real.startsWith(PUBLIC_DIR + sep))) {
    sendNotFoundPage(req, res);
    return;
  }

  let body;
  try {
    body = readFileSync(real);
  } catch {
    sendNotFoundPage(req, res);
    return;
  }

  sendBuffer(req, res, 200, body, {
    'Content-Type': contentTypeFor(real),
    'Cache-Control': 'no-cache',
  });
}

function readJsonBody(req) {
  return new Promise((resolvePromise, rejectPromise) => {
    const chunks = [];
    let size = 0;
    let tooLarge = false;

    req.on('data', (chunk) => {
      size += chunk.length;
      if (size > MAX_BODY_BYTES) {
        tooLarge = true;
        chunks.length = 0;
        if (size > MAX_BODY_BYTES * 8) {
          req.destroy();
        }
        return;
      }
      chunks.push(chunk);
    });

    req.on('error', (err) => {
      rejectPromise(Object.assign(err, { statusCode: 400 }));
    });

    req.on('end', () => {
      if (tooLarge) {
        rejectPromise(Object.assign(new Error('request body too large (limit 64 KB)'), { statusCode: 413 }));
        return;
      }
      const raw = Buffer.concat(chunks).toString('utf8');
      if (raw.trim() === '') {
        resolvePromise({});
        return;
      }
      try {
        const parsed = JSON.parse(raw);
        if (parsed === null || typeof parsed !== 'object' || Array.isArray(parsed)) {
          rejectPromise(Object.assign(new Error('request body must be a JSON object'), { statusCode: 400 }));
          return;
        }
        resolvePromise(parsed);
      } catch {
        rejectPromise(Object.assign(new Error('malformed JSON body'), { statusCode: 400 }));
      }
    });
  });
}

function countOption(body) {
  const raw = body.count === undefined || body.count === null ? 1 : Number(body.count);
  if (!Number.isInteger(raw) || raw < 1 || raw > 10) {
    throw Object.assign(new Error('count must be an integer between 1 and 10'), { statusCode: 400 });
  }
  return raw;
}

async function handleGenerate(req, res, body) {
  const mode = body.mode === undefined || body.mode === null ? 'memorable' : String(body.mode);
  if (mode !== 'memorable' && mode !== 'random') {
    sendError(req, res, 400, `unknown mode "${mode}"`);
    return;
  }

  let count;
  try {
    count = countOption(body);
  } catch (err) {
    sendError(req, res, err.statusCode || 400, err.message);
    return;
  }

  let entropy;
  try {
    entropy = estimateEntropy(mode, body);
  } catch (err) {
    sendError(req, res, 400, err.message);
    return;
  }

  const passwords = [];
  for (let i = 0; i < count; i += 1) {
    let value;
    try {
      value = mode === 'memorable' ? generateMemorizable(body) : generateRandom(body);
    } catch (err) {
      sendError(req, res, 400, err.message);
      return;
    }
    passwords.push({ value, mode, entropy });
  }

  sendJson(req, res, 200, { mode, count, passwords, entropy });
}

async function handleApi(req, res, pathname) {
  if (pathname === '/api/meta') {
    if (req.method !== 'GET' && req.method !== 'HEAD') {
      sendError(req, res, 405, 'method not allowed');
      return;
    }
    sendJson(req, res, 200, { lists: listMeta() });
    return;
  }

  if (pathname === '/api/generate') {
    if (req.method !== 'POST') {
      sendError(req, res, 405, 'method not allowed');
      return;
    }
    let body;
    try {
      body = await readJsonBody(req);
    } catch (err) {
      sendError(req, res, err.statusCode || 400, err.message);
      return;
    }
    await handleGenerate(req, res, body);
    return;
  }

  sendError(req, res, 404, 'not found');
}

const server = createServer((req, res) => {
  let pathname = '/';
  try {
    pathname = new URL(req.url || '/', 'http://localhost').pathname;
  } catch {
    sendError(req, res, 400, 'bad request');
    return;
  }

  if (pathname === '/healthz') {
    if (req.method !== 'GET' && req.method !== 'HEAD') {
      sendError(req, res, 405, 'method not allowed');
      return;
    }
    sendJson(req, res, 200, { status: 'ok' });
    return;
  }

  if (pathname.startsWith('/api/')) {
    handleApi(req, res, pathname).catch((err) => {
      sendError(req, res, 500, err && err.message ? err.message : 'internal error');
    });
    return;
  }

  if (req.method !== 'GET' && req.method !== 'HEAD') {
    sendError(req, res, 405, 'method not allowed');
    return;
  }

  serveStatic(req, res, pathname);
});

server.listen(PORT, HOST, () => {
  console.log(`reze-test listening on http://${HOST}:${PORT}`);
});