/**
 *  @file operator-authenticate.cc
 *  @brief Implementation of the AUTHENTICATE command, incl. CRAM-MD5.
 *  @author Andreas Aardal Hanssen, Erwin Hoffmann
 *  @date 2002-2005, 2023
 */

#include "authenticate.h"
#include "base64.h"
#include "convert.h"
#include "depot.h"
#include "globals.h"
#include "iodevice.h"
#include "iofactory.h"
#include "operators.h"
#include "recursivedescent.h"
#include "session.h"

#include <cstring>
#include <string>

using namespace Binc;
using std::endl;
using std::string;

AuthenticateOperator::AuthenticateOperator(void) {}

AuthenticateOperator::~AuthenticateOperator(void) {}

const string AuthenticateOperator::getName(void) const
{
  return "AUTHENTICATE";
}

int AuthenticateOperator::getState(void) const
{
  return Session::NONAUTHENTICATED;
}

Operator::ProcessResult AuthenticateOperator::Login(string &username, string &password)
{
  Session &session = Session::getInstance();

  bincClient << "+ " << base64encode("User Name") << endl;
  bincClient.flush();

  // Read user name
  string b64usr;
  for (;;) {
    char c;
    if (!bincClient.readChar(&c)) {
      session.setLastError("unexpected EOF");
      return BAD;
    }
    if (c == '\n') break;
    b64usr += c;
  }

  if (b64usr != "" && b64usr[0] == '*') {
    session.setLastError("Authentication cancelled by user");
    return NO;
  }

  bincClient << "+ " << base64encode("Password") << endl;
  bincClient.flush();

  // Read password
  string b64pwd;
  for (;;) {
    char c;
    if (!bincClient.readChar(&c)) {
      session.setLastError("unexpected EOF");
      return BAD;
    }
    if (c == '\n') break;
    b64pwd += c;
  }

  if (b64pwd != "" && b64pwd[0] == '*') {
    session.setLastError("Authentication cancelled by user");
    return NO;
  }

  username = base64decode(b64usr);
  password = base64decode(b64pwd);

  return OK;
}

Operator::ProcessResult AuthenticateOperator::Plain(string &username, string &password)
{
  Session &session = Session::getInstance();

  bincClient << "+ " << endl;
  bincClient.flush();

  string b64;
  for (;;) {
    char c;
    if (!bincClient.readChar(&c)) {
      session.setLastError("unexpected EOF");
      return BAD;
    }
    if (c == '\n') break;

    b64 += c;
  }

  if (b64.size() >= 1 && b64[0] == '*') {
    session.setLastError("Authentication cancelled by user");
    return NO;
  }

  string plain = base64decode(b64);
  string::size_type pos = 0;

  if ((pos = plain.find('\0')) == string::npos) {
    session.setLastError("Authentication failed. In PLAIN mode, "
                         "there must be at least two null characters "
                         "in the input string, but none were found");
    return NO;
  }

  plain = plain.substr(pos + 1);
  if ((pos = plain.find('\0')) == string::npos) {
    session.setLastError("Authentication failed. In PLAIN mode, "
                         "there must be at least two null characters "
                         "in the input string, but only one was found");
    return NO;
  }

  username = plain.substr(0, pos);
  password = plain.substr(pos + 1);

  return OK;
}

Operator::ProcessResult AuthenticateOperator::Cram(string &username, string &password, string &challenge)
{
  Session &session = Session::getInstance();

  // generate challenge first: <pid.time@fqdn> and deploy it to authenticator
  time_t timer;
  struct tm y2k = {};
  int timestamp;
  y2k.tm_hour = 0;
  y2k.tm_min = 0;
  y2k.tm_sec = 0;
  y2k.tm_year = 100;
  y2k.tm_mon = 0;
  y2k.tm_mday = 1;

  time(&timer); /* get current time; same as: timer = time(NULL)  */
  timestamp = difftime(timer, mktime(&y2k));

  challenge += "<";
  challenge += std::to_string(session.getPid());
  challenge += ".";
  challenge += std::to_string(timestamp);
  challenge += "@";
  challenge += session.getEnv("TCPLOCALHOST");
  challenge += ">";

  bincClient << "+ " << base64encode(challenge) << endl;
  bincClient.flush();

  // Read response
  string b64;
  for (;;) {
    char c;
    if (!bincClient.readChar(&c)) return BAD;
    if (c == '\n') break;
    b64 += c;
  }

  // Disentangle response
  string response = base64decode(b64);
  string::size_type pos = 0;

  if ((pos = response.find(' ')) == string::npos) {
    session.setLastError("Authentication failed. In CRAM-MD5 mode, "
                         "there must be a white space in the "
                         "input string between username and digest");
    return NO;
  }

  username = response.substr(0, pos);
  password = response.substr(pos + 1);

  return OK;
}

Operator::ProcessResult AuthenticateOperator::process(Depot &depot, Request &command)
{
  Session &session = Session::getInstance();

  string authtype = command.getAuthType();
  uppercase(authtype);

  string username;
  string password;
  string challenge;
  ProcessResult r = NOTHING;

  if (authtype == "LOGIN") {
    // we only allow this type of authentication over an unencryted connection
    // if it is explicitely commanded
    if (!session.command.ssl && !session.hasEnv("ALLOW_NONSSL_PLAINTEXT_LOGINS")) {
      session.setLastError("Plain text password authentication is disallowd. "
                           "Please enable StartTLS or TLS in your mail client.");
      return NO;
    }
    if ((r = Login(username, password)) != OK) return r;

  } else if (authtype == "PLAIN") {
    // we only allow this type of authentication over an TLS encrypted connection.
    if (!session.command.ssl && !session.hasEnv("ALLOW_NONSSL_PLAINTEXT_LOGINS")) {
      session.setLastError("Plain text password authentication is disallowd. "
                           "Please enable StartTLS or TLS in your mail client.");
      return NO;
    }
    if ((r = Plain(username, password)) != OK) return r;

  } else if (authtype == "CRAM-MD5") {
    // this type can be used even over unencrypted connections
    if ((r = Cram(username, password, challenge)) != OK) return r;

  } else {  // Any other disallowed
    session.setLastError("The authentication method " + toImapString(authtype)
                         + " is not supported. "
                           "Please try again with a different method. "
                           "There is built in support for \"PLAIN\" "
                           "and \"LOGIN\".");
    return NO;
  }

  putenv(strdup(("BINCIMAP_LOGIN=AUTHENTICATE+" + command.getTag()).c_str()));

  // put the username in the environment for logging purpose

  session.setEnv("USER", username.c_str());

  // the authenticate function calls a stub which does the actual
  // authentication. the function returns 0 (success), 1 (internal
  // error) or 2 (failed)

  switch (authenticate(depot, username, password, challenge)) {
  case 1:
    session.setLastError("An internal error occurred when you attempted "
                         "to log in to the IMAP server. Please contact "
                         "your system administrator.");
    return NO;
  case 2:
    session.setLastError("Login failed. Either your user name "
                         "or your password was wrong. Please try again, "
                         "and if the problem persists, please contact "
                         "your system administrator.");
    return NO;
  case 3:
    bincClient << "* BYE Timeout after " << IDLE_TIMEOUT << " seconds of inactivity." << endl;
    break;
  case -1:
    bincClient << "* BYE The server died unexpectedly. Please contact "
                  "your system administrator for more information."
               << endl;
    break;
  default:
    //       bincLog << "<" << username.c_str() << "> authenticated" << endl;
    break;
  }

  // auth was ok. go to logout state
  session.setState(Session::LOGOUT);
  return NOTHING;
}

Operator::ParseResult AuthenticateOperator::parse(Request &c_in) const
{
  Session &session = Session::getInstance();

  if (c_in.getUidMode()) return REJECT;

  Operator::ParseResult res;

  if ((res = expectSPACE()) != ACCEPT) {
    session.setLastError("Expected single SPACE after AUTHENTICATE");
    return res;
  }

  string authtype;
  if ((res = expectAtom(authtype)) != ACCEPT) {
    session.setLastError("Expected auth_type after AUTHENTICATE SPACE");
    return ERROR;
  }

  if ((res = expectCRLF()) != ACCEPT) {
    session.setLastError("Expected CRLF after AUTHENTICATE SPACE auth_type");
    return res;
  }

  c_in.setAuthType(authtype);

  c_in.setName("AUTHENTICATE");
  return ACCEPT;
}