import { X509Certificate } from 'crypto';
import * as http from 'http';
import * as https from 'https';
import * as net from 'net';
import * as tls from 'tls';

/**
 * The one HTTP client both accounting drivers use.
 *
 * Built on node:http(s) rather than global fetch because a self-hosted
 * Tahesab/Zarrin often serves a self-signed certificate, and fetch cannot be
 * given a CA without an extra dependency. The reference "solved" that with
 * `Http::withoutVerifying()` (SEC-17); here verification is ALWAYS on and the
 * admin can paste the installation's certificate instead.
 *
 * A pasted certificate is trusted two ways: as a CA (the normal chain and
 * hostname checks), and as a pin — when the server presents exactly that
 * certificate it is accepted whatever name it was issued for. Tahesab's own
 * certificate is self-signed for `localhost`, so a remote install reached by
 * IP can only be verified by the pin.
 *
 * Errors say whether the request may have reached the server. That decides
 * what the outbox may do next: a refused connection is safe to retry, a
 * timeout after the request went out is not (Zarrin has no idempotency key).
 */

export interface HttpRequest {
  method: 'GET' | 'POST';
  url: string;
  headers?: Record<string, string>;
  body?: string;
  timeoutMs: number;
  /** PEM CA certificate(s) to trust in addition to the system store. */
  ca?: string | null;
}

export interface HttpResponse {
  status: number;
  body: string;
}

export class AccountingHttpError extends Error {
  constructor(
    message: string,
    /** True when the request may have been received and acted on. */
    readonly ambiguous: boolean,
    readonly code?: string,
  ) {
    super(message);
    this.name = 'AccountingHttpError';
  }
}

const MAX_BODY_BYTES = 20 * 1024 * 1024;

const TLS_CERT_ERRORS = /CERT|SELF_SIGNED|UNABLE_TO_VERIFY|UNABLE_TO_GET_ISSUER/;

/** The PEM blocks in a pasted bundle, parsed; unparsable blocks are skipped. */
export function parsePemCertificates(pem: string | null | undefined): X509Certificate[] {
  const blocks = (pem ?? '').match(/-----BEGIN CERTIFICATE-----[\s\S]+?-----END CERTIFICATE-----/g) ?? [];
  const out: X509Certificate[] = [];
  for (const block of blocks) {
    try {
      out.push(new X509Certificate(block));
    } catch {
      // not a certificate — the CA list below will reject it too
    }
  }
  return out;
}

/** SHA-256 fingerprints, as Node prints them (`AB:CD:…`), of the pasted certificates. */
export function pinnedFingerprints(pem: string | null | undefined): Set<string> {
  return new Set(parsePemCertificates(pem).map((c) => c.fingerprint256));
}

function tlsErrorMessage(err: NodeJS.ErrnoException, pinned: boolean): string {
  if (err.code === 'ERR_TLS_CERT_ALTNAME_INVALID') {
    return pinned
      ? `گواهی سرور برای این آدرس صادر نشده و با گواهی ثبت‌شده در تنظیمات هم یکی نیست (${err.code}) — اگر گواهی سرور عوض شده، در بخش «گواهی امنیتی سرور» «بررسی دوباره» را بزنید`
      : `گواهی TLS سرور برای این آدرس صادر نشده (${err.code}) — در تب «اتصال»، بخش «گواهی امنیتی سرور»، «بررسی گواهی سرور» را بزنید و پس از تطبیق اثرانگشت تأیید و ذخیره کنید`;
  }
  return pinned
    ? `گواهی فعلی سرور با گواهی ثبت‌شده در تنظیمات یکی نیست (${err.code}) — اگر گواهی سرور عوض شده، در بخش «گواهی امنیتی سرور» «بررسی دوباره» را بزنید`
    : `گواهی TLS سرور قابل‌اعتماد نیست (${err.code}) — در تب «اتصال»، بخش «گواهی امنیتی سرور»، «بررسی گواهی سرور» را بزنید و پس از تطبیق اثرانگشت تأیید و ذخیره کنید`;
}

export function httpRequest(req: HttpRequest): Promise<HttpResponse> {
  return send(req, false);
}

/**
 * One attempt. `fresh` = on a new connection: a server that closes idle
 * kept-alive connections (Zarrin v228 does) makes the next request on a pooled
 * one fail with ECONNRESET / "socket hang up" before it was received. That one
 * case is repeated once on a fresh connection; nothing else is ever retried.
 */
function send(req: HttpRequest, fresh: boolean): Promise<HttpResponse> {
  let url: URL;
  try {
    url = new URL(req.url);
  } catch {
    return Promise.reject(new AccountingHttpError('آدرس سرور حسابداری نامعتبر است', false, 'BAD_URL'));
  }
  const isHttps = url.protocol === 'https:';
  if (!isHttps && url.protocol !== 'http:') {
    return Promise.reject(new AccountingHttpError('آدرس باید با http یا https شروع شود', false, 'BAD_URL'));
  }

  const headers: Record<string, string | number> = { ...(req.headers ?? {}) };
  if (req.body !== undefined) headers['Content-Length'] = Buffer.byteLength(req.body);

  const options: https.RequestOptions = {
    method: req.method,
    hostname: url.hostname,
    port: url.port || (isHttps ? 443 : 80),
    path: `${url.pathname}${url.search}`,
    headers,
    ...(fresh ? { agent: false } : {}),
  };
  const pins = isHttps ? pinnedFingerprints(req.ca) : new Set<string>();
  if (isHttps) {
    options.rejectUnauthorized = true;
    if (req.ca && req.ca.trim()) {
      // Extra CA on top of the system store, never instead of verification.
      options.ca = [...tls.rootCertificates, req.ca];
      // Runs only after the chain verified. The exact pasted certificate is
      // accepted under any name; anything else gets the normal name check.
      // (Pooled sockets are keyed by `ca`, so a reused one had the same pins.)
      options.checkServerIdentity = (host, cert) =>
        pins.has(cert.fingerprint256) ? undefined : tls.checkServerIdentity(host, cert);
    }
  }

  return new Promise<HttpResponse>((resolve, reject) => {
    let connected = false;
    let settled = false;
    const finish = (fn: () => void) => {
      if (settled) return;
      settled = true;
      clearTimeout(timer);
      fn();
    };

    const client = isHttps ? https : http;
    const request = client.request(options, (res) => {
      const chunks: Buffer[] = [];
      let size = 0;
      res.on('data', (chunk: Buffer) => {
        size += chunk.length;
        if (size > MAX_BODY_BYTES) {
          request.destroy();
          finish(() => reject(new AccountingHttpError('پاسخ سرور حسابداری بیش از حد بزرگ است', true, 'TOO_LARGE')));
          return;
        }
        chunks.push(chunk);
      });
      res.on('end', () =>
        finish(() => resolve({ status: res.statusCode ?? 0, body: Buffer.concat(chunks).toString('utf8') })),
      );
      res.on('error', (err) => finish(() => reject(new AccountingHttpError(err.message, true, 'RESPONSE'))));
    });

    request.on('socket', (socket) => {
      // A kept-alive socket is already connected; listening on it again would
      // pile up a listener per request.
      if (!(socket as { connecting?: boolean }).connecting) {
        connected = true;
        return;
      }
      socket.once(isHttps ? 'secureConnect' : 'connect', () => {
        connected = true;
      });
    });

    const timer = setTimeout(() => {
      request.destroy();
      finish(() =>
        reject(
          new AccountingHttpError(
            connected ? 'پاسخ سرور حسابداری در زمان مقرر نرسید' : 'اتصال به سرور حسابداری برقرار نشد (timeout)',
            connected,
            'TIMEOUT',
          ),
        ),
      );
    }, req.timeoutMs);

    request.on('error', (err: NodeJS.ErrnoException) => {
      if (!fresh && request.reusedSocket && err.code === 'ECONNRESET') {
        finish(() => resolve(send(req, true)));
        return;
      }
      // Node's own text for these suggests flags that do not apply here.
      const text = isHttps && err.code && TLS_CERT_ERRORS.test(err.code) ? tlsErrorMessage(err, pins.size > 0) : err.message;
      finish(() => reject(new AccountingHttpError(text, connected, err.code)));
    });

    if (req.body !== undefined) request.write(req.body);
    request.end();
  });
}

export interface ServerCertificate {
  pem: string;
  subject: string;
  issuer: string;
  subjectAltName: string | null;
  validFrom: string;
  validTo: string;
  expired: boolean;
  fingerprint256: string;
  selfSigned: boolean;
  /** Valid chain to a system CA and issued for this host: no pin needed. */
  trustedBySystem: boolean;
}

/**
 * Reads the certificate an https server presents, WITHOUT trusting it, so the
 * admin can compare its fingerprint with the one on the accounting server and
 * pin it. Nothing but the TLS handshake is sent.
 */
export function fetchServerCertificate(baseUrl: string, timeoutMs: number): Promise<ServerCertificate> {
  let url: URL;
  try {
    url = new URL(baseUrl);
  } catch {
    return Promise.reject(new AccountingHttpError('آدرس سرور حسابداری نامعتبر است', false, 'BAD_URL'));
  }
  if (url.protocol !== 'https:') {
    return Promise.reject(new AccountingHttpError('این آدرس https نیست؛ گواهی ندارد', false, 'NOT_HTTPS'));
  }
  const host = url.hostname.replace(/^\[|\]$/g, '');
  return new Promise<ServerCertificate>((resolve, reject) => {
    const socket = tls.connect({
      host,
      port: Number(url.port || 443),
      servername: net.isIP(host) ? undefined : host,
      rejectUnauthorized: false,
    });
    const timer = setTimeout(() => {
      socket.destroy();
      reject(new AccountingHttpError('اتصال به سرور حسابداری برقرار نشد (timeout)', false, 'TIMEOUT'));
    }, timeoutMs);
    socket.once('secureConnect', () => {
      clearTimeout(timer);
      const peer = socket.getPeerCertificate();
      const chainOk = socket.authorized;
      socket.end();
      if (!peer?.raw) {
        reject(new AccountingHttpError('سرور گواهی ارسال نکرد', false, 'NO_CERT'));
        return;
      }
      const cert = new X509Certificate(peer.raw);
      const nameOk = net.isIP(host) ? !!cert.checkIP(host) : !!cert.checkHost(host);
      const b64 = peer.raw.toString('base64').match(/.{1,64}/g)!.join('\n');
      resolve({
        pem: `-----BEGIN CERTIFICATE-----\n${b64}\n-----END CERTIFICATE-----`,
        subject: cert.subject,
        issuer: cert.issuer,
        subjectAltName: cert.subjectAltName ?? null,
        validFrom: cert.validFrom,
        validTo: cert.validTo,
        expired: new Date(cert.validTo).getTime() < Date.now(),
        fingerprint256: cert.fingerprint256,
        // checkIssued() also wants keyCertSign, which Tahesab's certificate lacks.
        selfSigned: cert.subject === cert.issuer && cert.verify(cert.publicKey),
        trustedBySystem: chainOk && nameOk,
      });
    });
    socket.once('error', (err: NodeJS.ErrnoException) => {
      clearTimeout(timer);
      reject(new AccountingHttpError(err.message, false, err.code));
    });
  });
}

/**
 * Parses a JSON body that may carry junk around it. Tahesab replies have been
 * seen with a BOM, raw control characters and unescaped backslashes inside
 * strings (henza_server TahesabController::test had to scrub them the same
 * way before json_decode would accept the body).
 */
export function parseLooseJson(body: string): unknown {
  try {
    return JSON.parse(body);
  } catch {
    // fall through to the scrubbed attempt
  }
  let raw = body.replace(/^/, '');
  raw = raw.replace(/[\x00-\x08\x0B\x0C\x0E-\x1F\x7F]/g, '');
  raw = raw.replace(/\\(?!["\\/bfnrtu])/g, '-');
  const start = raw.search(/[{[]/);
  if (start > 0) raw = raw.slice(start);
  return JSON.parse(raw);
}