import { lstat, readFile } from 'node:fs/promises';
import { constants } from 'node:fs';
import { open } from 'node:fs/promises';
import { X509Certificate } from 'node:crypto';
import type { PoolConfig } from 'pg';

export function custodyStorage(env: NodeJS.ProcessEnv = process.env): 'sqlite' | 'postgres' {
  const value = env.WIKIDECK_CUSTODY_STORAGE ?? 'sqlite';
  if (value !== 'sqlite' && value !== 'postgres') throw new Error('Invalid custody storage backend');
  return value;
}
async function secretFile(path: string | undefined): Promise<string> {
  if (!path) throw new Error('Custody PostgreSQL secret file is required');
  const info = await lstat(path);
  if (!info.isFile() || info.isSymbolicLink() || info.size > 16384 || info.size === 0) throw new Error('Invalid PostgreSQL secret file');
  if (process.platform !== 'win32' && (info.mode & 0o077) !== 0) throw new Error('PostgreSQL secret file permissions are too broad');
  return (await readFile(path, 'utf8')).trim();
}
function derLength(bytes: Buffer, offset: number): { length: number; next: number } {
  if (offset >= bytes.length) throw new Error('Invalid certificate DER length');
  const first = bytes[offset];
  if (first < 0x80) return { length: first, next: offset + 1 };
  const count = first & 0x7f;
  if (count === 0 || count > 4 || offset + count >= bytes.length) throw new Error('Invalid certificate DER length');
  let length = 0;
  for (let i = 1; i <= count; i++) length = length * 256 + bytes[offset + i];
  return { length, next: offset + count + 1 };
}
function derElement(bytes: Buffer, offset: number): { tag: number; start: number; end: number; next: number } {
  if (offset >= bytes.length) throw new Error('Invalid certificate DER');
  const tag = bytes[offset], size = derLength(bytes, offset + 1), end = size.next + size.length;
  if (end > bytes.length) throw new Error('Invalid certificate DER');
  return { tag, start: size.next, end, next: end };
}
function validateCaCertificate(pem: Buffer): string {
  const certificate = new X509Certificate(pem);
  const now = Date.now();
  if (!Number.isFinite(Date.parse(certificate.validFrom)) || !Number.isFinite(Date.parse(certificate.validTo)) ||
      now < Date.parse(certificate.validFrom) || now > Date.parse(certificate.validTo)) {
    throw new Error('PostgreSQL CA certificate is not currently valid');
  }
  if (certificate.subject !== certificate.issuer || !certificate.verify(certificate.publicKey)) {
    throw new Error('PostgreSQL CA certificate must be a valid self-signed trust anchor');
  }
  const key = certificate.publicKey;
  if (key.asymmetricKeyType !== 'rsa' || (key.asymmetricKeyDetails?.modulusLength ?? 0) < 2048) {
    throw new Error('PostgreSQL CA certificate key must be RSA-2048 or stronger');
  }
  const der = certificate.raw;
  const outer = derElement(der, 0);
  if (outer.tag !== 0x30) throw new Error('Invalid PostgreSQL CA certificate DER');
  const tbs = derElement(der, outer.start);
  const signatureAlgorithm = derElement(der, tbs.next);
  if (signatureAlgorithm.tag !== 0x30) throw new Error('Invalid PostgreSQL CA signature algorithm');
  const oid = derElement(der, signatureAlgorithm.start);
  if (oid.tag !== 0x06) throw new Error('Invalid PostgreSQL CA signature algorithm');
  const signatureOid = der.subarray(oid.start, oid.end).toString('hex');
  const weakSignatureOids = new Set(['2a864886f70d010104', '2b0e03021a', '2b0e03021b']);
  if (weakSignatureOids.has(signatureOid)) throw new Error('PostgreSQL CA certificate uses a weak signature algorithm');
  return pem.toString('utf8');
}
async function publicCaFile(path: string | undefined): Promise<string | undefined> {
  if (!path) return undefined;
  const file = await open(path, constants.O_RDONLY | constants.O_NOFOLLOW);
  try {
    const info = await file.stat();
    if (!info.isFile() || info.size < 1 || info.size > 64 * 1024) throw new Error('Invalid PostgreSQL CA file');
    // A CA certificate is public trust material; mode 0644 is expected. It is not a database credential.
    const bytes = await file.readFile();
    return validateCaCertificate(bytes);
  } finally { await file.close(); }
}
/** No URL logging, no TLS options in a connection string overriding verified transport. */
export async function postgresConfig(env: NodeJS.ProcessEnv = process.env): Promise<PoolConfig> {
  try {
    const url = new URL(await secretFile(env.WIKIDECK_CUSTODY_PG_URL_FILE));
    if (!['postgres:', 'postgresql:'].includes(url.protocol) || !url.hostname || url.search || url.hash ||
      !/^\/[a-zA-Z0-9_-]+$/.test(url.pathname)) throw new Error('Invalid PostgreSQL URL');
    const insecure = env.WIKIDECK_CUSTODY_PG_LOCAL_TEST === '1';
    const transport = env.WIKIDECK_CUSTODY_PG_TRANSPORT ?? 'tls';
    if (transport !== 'tls' && transport !== 'infrastructure') throw new Error('Invalid PostgreSQL transport');
    const infrastructure = transport === 'infrastructure';
    const acknowledgement = env.WIKIDECK_CUSTODY_PG_INFRASTRUCTURE_ACK;
    if (infrastructure) {
      if (acknowledgement !== 'encrypted-authenticated-path-enforced' || insecure || env.WIKIDECK_CUSTODY_PG_CA_FILE) {
        throw new Error('Infrastructure transport requires explicit acknowledgement without conflicting TLS/test settings');
      }
    } else if (acknowledgement !== undefined) throw new Error('Infrastructure acknowledgement without infrastructure transport');
    if (env.WIKIDECK_CUSTODY_PG_LOCAL_TEST !== undefined && !insecure) throw new Error('Invalid local-test switch');
    if (insecure && !['127.0.0.1', 'localhost', '[::1]'].includes(url.hostname)) throw new Error('Non-TLS test connections must be loopback');
    if (!insecure && (!url.username || !url.password)) throw new Error('PostgreSQL credentials required');
    if (url.port && (!/^\d+$/.test(url.port) || Number(url.port) < 1 || Number(url.port) > 65535)) throw new Error('Invalid PostgreSQL port');
    const ca = await publicCaFile(env.WIKIDECK_CUSTODY_PG_CA_FILE);
    return { host: url.hostname.replace(/^\[|\]$/g, ''), port: url.port ? Number(url.port) : 5432,
      database: url.pathname.slice(1), user: decodeURIComponent(url.username), password: decodeURIComponent(url.password),
      // Infrastructure mode is explicit plaintext on the driver's hop. It does NOT configure or
      // verify a service mesh, peer identity, network policy, or encryption outside this process.
      ssl: insecure || infrastructure ? false : { rejectUnauthorized: true, ...(ca ? { ca } : {}) },
      max: 4, connectionTimeoutMillis: 5000, idleTimeoutMillis: 10000,
      statement_timeout: 10000, lock_timeout: 3000, idle_in_transaction_session_timeout: 10000,
      application_name: 'wikideck-custody', options: '-c search_path=wk_custody,pg_catalog' };
  } catch { throw new Error('Invalid or inaccessible custody PostgreSQL configuration; check secret files and explicit transport policy'); }
}