//////////////////
// skrewt.c
//
// scrutinize email
//

#include <iostream>
#include <stdlib.h>             /* for exit() */
#include <string>               /* for strcmp() */
#include <ctype.h>              /* toupper */
#include <signal.h>

#include <stdio.h>              /* perror */
#include <sstream>
#include <vector>
#include <list>

using namespace std;

void usage(const int sts){
  (sts ? cerr : cout) <<
"Usage: skrewt [options]\n"
"\n"
"  Scrutinizes email.  Reads stdin, copies it to stdout.\n"
"  Exit result 0 means good, 21 means rejection (spam).\n"
"  Writes reason for rejection to stderr.\n"
"\n"
"  Typically used as a filter in a pipeline, along with spamc -E\n"
"  Options\n"
"    -help              print this msg (and exit immediately).\n"
"    -maxsize ii        msg size in bytes; anything bigger will be rejected.\n"
"    -error-exit        exit early if errors have been detected.\n"
"\n"
"  Messages containing the string '-please-bounce-this-' will be rejected.\n"
"  Messages with no date will be rejected.\n"
;
  exit(sts);
}

#include "qq_exit_codes.h"
#include "utils.h"

/////////////////////////////////////////////////////////
// Case insensitive comparison of strings

class lessthan_foldcase{
public:
  bool operator() (const std::string& a, const std::string& b) const {
    size_t a_len = a.length();
    size_t b_len = b.length();

    size_t lim = a_len < b_len ? a_len : b_len;

    for (size_t i=0; i<lim; ++i)
    {
            char cha = toupper(a[i]);
            char chb = toupper(b[i]);

            if (cha < chb) return true;
            if (cha > chb) return false;
    }
    // here if one is an extension of the other
    if ( a_len < b_len ) return true;
    return false;
  }
};


// Returns negative if a is less than b in alphabetical order
// returns 0 if they are the same, or positive if a is greater.
// Like perl cmp operator, but ignores case.
int cmp_casefold(const std::string& a, const std::string& b) {
  string::const_iterator aa, bb;
  aa = a.begin();
  bb = b.begin();
  while (aa != a.end() && bb != b.end()){
    char ca = tolower(*aa++);
    char cb = tolower(*bb++);
    if (ca != cb) return ca < cb ? -2 : 2;
  }
  if (aa != a.end()) return 1;          // a is longer
  if (bb != b.end()) return -1;         // b is longer
  return 0;
}

string noCR(const string bar){
  string foo(bar);
  int len = foo.length();
  if (len){
    if (foo[len-1] == '\r') {
      foo.erase(len-1);
    }
  }
  return foo;
}

void maybe_exeunt(const int sts, const int really){
  if (!really) return;
  if (sts == ex_good) exit(sts);

  const char* foo = getenv("HI_Q_GROUP");
  if (!foo) exit(sts);

// No point in signalling ourself:
  sighandler_t rslt = signal(SIGUSR1, SIG_IGN);
  if (rslt == SIG_ERR) {
    cerr << "error setting signal" << endl;
  }
  int k = kill(-atoi(foo), SIGUSR1);
  if (k) {
    cerr << "kill failed on group " << atoi(foo) << " ... ";
    perror(0);
  }
  exit(sts);
}

void exeunt(const int sts){
  maybe_exeunt(sts, 1);
}

string progname, progid;
int mypid;

/* Content-Type: text/plain; charset="us-ascii"                                         */
/* Content-Type: multipart/mixed; boundary="1170861315-1262462055-1341954763=:92165"    */
//
void parse_content(const string type_spec_line, string &maintype, string &boundary) {
  //xxx cerr << "parser called with: " << type_spec_line << endl;
  string get_type(type_spec_line);

  size_t where = get_type.find_first_of(" \t;\n");
  string rest;
  if (where == string::npos) {
    // keep whole string
  }
  else {
    rest = get_type.substr(where+1);
    get_type = get_type.substr(0,where);
  }
  where = get_type.find("/");
  if (where == string::npos){
    maintype = "";
    cerr << "could not find / in " << get_type << endl;
  } else {
    maintype = get_type.substr(0, where);
  }

// now need to find boundary

  string srch = "boundary=";
  where = rest.find(srch);
  if (where != string::npos) {
    where += srch.length();
    boundary = rest.substr(where);
    if (boundary[0] == '"') {
      boundary = boundary.substr(1);
      where = boundary.find_first_of("\"");
    } else {
      where = boundary.find_first_of(" \t;\n");
    }
    if (where == string::npos) {
      /* do nothing, boundary=boundary as a whole */
    } else {
      boundary = boundary.substr(0, where);
    }
  } else {
    //xxxxxxx cerr << "boundary= not found in " << type_spec_line << endl;
  }
}

string join(const string sep, const list<string> stuff){
  string rslt;
  for (list<string>::const_iterator ptr = stuff.begin();
        ptr != stuff.end(); ptr++){
    if (rslt.length()) rslt += sep;
    rslt += *ptr;
  }
  return rslt;
}

class skrewt{
public:
  string boundary;
  string to;
  string from;
  string subject;
  string date;
  string message_id;
  string content_type;
  int msgsize;
  vector<string> bigbuf;
  int saw_blank_line;
  int recno;

  int maxsize;
  int error_exit;
  int mid_required;

  // constructor
  skrewt()
  : boundary("x-xx-x"), msgsize(0), saw_blank_line(0), recno(0),
    maxsize(1000*1000), error_exit(0), mid_required(0)
  {}

  int headers();
  int interstage();
  int body();
};

int skrewt::headers(){
  //xxxx cerr << progid << " begins" << endl;
  for (;;){             // outer loop over all records in the header
    if (cin.eof()) break;
    if (cin.bad()) return 1;

    string line;
// on fail, go back to top of outer loop and check for eof versus bad
    if (getline(cin, line).fail()) continue;
    msgsize += line.length()+1;
    if (msgsize > maxsize) {
      cerr << progid << " rejection: bigger than " << maxsize << endl;
      exeunt(ex_spam);
    }
    cout << line << endl;
    bigbuf.push_back(line);
    string headrec = noCR(line);       // for a folded record, this is the first line

    for (;;) {        // inner loop to build a multi-line record e.g. folded record:
      if (cin.eof()) break;
      if (cin.bad()) return 1;
      char ch;
      if (cin.get(ch).fail()) continue;
      cin.putback(ch);
      if (ch != ' ' && ch != '\t') break;
      string line;
// on fail, go back to top of inner loop and check for eof versus bad
      if (getline(cin, line).fail()) continue;
      msgsize += line.length()+1;
      if (msgsize > maxsize) {
        cerr << progid << " rejection: bigger than " << maxsize << endl;
        exeunt(ex_spam);
      }
      cout << line << endl;
      bigbuf.push_back(line);
      headrec += "\n" + noCR(line);
    }
// here with a fully assembled header record
// headrec (unlike line) contains no DOS CR characters
    int len = headrec.length();
    if (len == 0) {
      saw_blank_line = 1;
      break;            // no more headers in this message
    }

// here if it's a header line
    string headword;
    string rest;
    size_t where = headrec.find(":");
    if (where != string::npos) {
      headword = headrec.substr(0, where);
      rest = ltrim(headrec.substr(1+where));
    }
    headword = toLower(headword);
    if (0){
    } else if (headword == "from") {
      from = rest;
    } else if (headword == "to") {
      to = rest;
    } else if (headword == "message-id") {
      message_id = rest;
    } else if (headword == "date") {
      date = rest;
    } else if (headword == "subject") {
      subject = rest;
    } else if (headword == "content-type") {
      content_type = rest;
    }
    //xxxx  cout << headrec.length() << " ... ";
    recno++;
    if (0) if (recno <= 6) cerr << progid << "#" << recno
        << " " << headrec << endl;
  }
  return 0;
}

int skrewt::interstage(){
  if (saw_blank_line) {/* ignore */}
  cerr << progid <<" Mid '" << message_id << "'" << endl;

// The logic here is:  In order:
// 1) If whitelisted, accept.  No greylisting, no spam-checking.
// 2) If blacklisted, reject.  No greylisting, no spam-checking.
// 3) If good reputation, spam-check it and send it on its way.
// 4) If no reputation, greylist.
// 5) If bad reputation, ????

// Expanding item 3 to the next level of detail:
//  3a) If some domain vouches for this sender-IP via SPF,
//   then the reputation is bound to the domain.
//  3c) If some domain vouches for the message vie DKIM,
//   then the reputation is bound to the domain.
//  3d) If no SPF or DKIM, then the reputation attaches
//   to the sender-IP.

// Expanding item 4 to the next level of detail:
//  4a) If the greylisting database says this message is ripe
//   spam-check it.  If it's OK, use it to count toward reputation.
//  4b) If it is previously unseen or too old, start greylisting
//   timer from scratch.  Reject with temporary error.
//  4c) If it is in the "green" state, let the timer
//   continue from where it is.  Reject with temporary error.

  list<string> badnews;

  if (subject.find("-please-bounce-this-") != string::npos) {
    badnews.push_back("by request");
  }

  if (!date.length()) {
    badnews.push_back("no date");
  }

  if (mid_required && !message_id.length()) {
    badnews.push_back("no message-id");
  }

  if (badnews.size()){
    cerr << progid << " " << join(", ", badnews) << endl;
    if (error_exit){
      cerr << progid << " '" << from
             << "' to '" << to
             << "'" << endl;
      exeunt(ex_spam);
    }
  }
  return 0;
}

int skrewt::body(){
  string main_contype;
  if (content_type.length())
    parse_content(content_type, main_contype, boundary);
// some slightly-useful booleans:
  int currently_text = main_contype == "text";
  int main_multipart = main_contype == "multipart";

// early-stage thinking has been done.
// Now spew the rest of the message
  //xxxx cerr << "body begins: " << main_contype << " " << currently_text << " " << boundary << endl;
  int in_subheads(0);
  int textlines(0);

  for (;;){             // outer loop over all lines in the body
    if (cin.eof()) break;
    if (cin.bad()) return 1;
    string line;
// on fail, go back to top of outer loop and check for eof versus bad
    if (getline(cin, line).fail()) continue;
    msgsize += line.length()+1;
    if (msgsize > maxsize) {
      cerr << progid << " rejection: bigger than " << maxsize << endl;
      maybe_exeunt(ex_spam, error_exit);
    }
    bigbuf.push_back(line);
    cout << line << endl;
    if (in_subheads){
      if (line == "" || line == "\r") in_subheads = 0;
    }
    if (in_subheads){
        string sub_contype;
        string junk;
// in principle could worry about folded headers,
// but in this application it doesn't actually matter
        string headword;
        string rest;
        size_t where = line.find(":");
        if (where != string::npos) {
          headword = line.substr(0, where);
          rest = ltrim(line.substr(1+where));
        }
        headword = toLower(headword);
        if (headword == "content-type") {
          parse_content(rest, sub_contype, junk);
          currently_text = sub_contype == "text";
          //xxxx cerr << "setting contype '" << sub_contype << "' " << currently_text << " ... " << textlines << endl;
        }
    } else {
      if (main_multipart && line == "--" + boundary) {
        //xxxx cerr << "found subhead boundary" << endl;
        in_subheads = 1;
        continue;
      }
      if (currently_text) textlines++;
    }
  }

  if (0) cerr << "textlines: " << textlines << endl;
  if (!textlines) {
    cerr << progid << " rejection: no text: " << error_exit << endl;
    maybe_exeunt(ex_spam, error_exit);
  }
  cerr << progid << " normal completion" << endl;
  return(ex_good);
}

////////////////////////////////////////////////////////////
int main(int _argc, const char** _argv){
////  pid_t pid = getpid();
////  cout << pid << endl;
////  cout << getpgid(pid) << endl;
  int argc(_argc);
  const char **argv(_argv);
  {
    progname = *argv++; argc--;
    mypid = getpid();
    stringstream binder;
    binder << basename(progname) << "[" << mypid << "]";
    progid = binder.str();
  }

  skrewt mysk;

  while (argc) {
    string arg(*argv); argv++; argc--;
    if (arg.substr(0,2) == "--") arg = arg.substr(1);
    if (prefix(arg, "-help")) {
      usage(0);
    }
    if (0) {
    } else if (prefix(arg, "-mid-required")) {
      mysk.mid_required++;
    } else if (prefix(arg, "-error-exit")) {
      mysk.error_exit++;
    } else if (prefix(arg, "-maxsize")) {
      if (!argc) {
        cerr << "Option -maxsize requires an argument" << endl;
        exit(ex_usage);
      }
      mysk.maxsize = atoi(*argv); argv++; argc--;
    } else if (arg.substr(0,1) == "-") {
      cerr << "Unrecognized option '" << arg << "'" << endl;
      cerr << "For help, try:  " << progname << " -help" << endl;
      exit(ex_usage);
    } else {
      cerr << "Extraneous verbiage '" << arg << "'" << endl;
      cerr << "For help, try:  " << progname << " -help" << endl;
      exit(ex_usage);
    }
  }

  int rslt = mysk.headers();
  if (rslt) return rslt;

// Headers are done.
// Do some early-stage thinking.

  rslt = mysk.interstage();
  if (rslt) return rslt;

  rslt = mysk.body();
  return rslt;

}