//////////////////////////////////

#include <iostream>
using namespace std;

void usage() {
  cout << R"EoF(
Typical usage:
:; ./timestamp -of foo.csv

Options include:
  -h                    # print this message (and immediately exit)
  -pinout               # show wiring diagram (and immediately exit)
  -ofile $fn            # send principle output to file $fn
                        # (for stdout, use "-")
  -rts $b               # set the RTS pin to $b (0 or 1)
  -dtr $b               # set the DTR pin to $b (0 or 1)
  -flip                 # repeatedly toggle the TXD pin
  -flip -flip           # toggle TXD, suppress normal output
  -ival $nnn            # cycle-time of the flip (in microseconds)
  -verbosity            # increase verbosity
  -device $dev          # use device to take data [default /dev/ttyS0]
  -local $b             # local means ignore DSR/DCD (recommended)

Options can be abbreviated as much as you dare.
)EoF";
}

void pinout() {
  cout << R"EoF(
       ** MALE (computer) (5i, 3o) **
                        1       DCDi
        DSRi       6
                        2       RXDi
        RTSo       7
                        3       TXDo
        CTSi       8
                        4       DTRo
        RNGi       9
                        5       GND


       ** FEMALE (modem) (3i, 5o) **
                        5       GND
        RNGo       9
                        4       DTRi
        CTSo       8
                        3       TXDi
        RTSi       7
                        2       RXDo
        DSRo       6
                        1       DCDo


            ** Observed Crossover Cable (F/F) **
        DTE     DSE                     DSE     DTE
        logic   pin                     pin     logic
        far     near                    near    far
                                5       GND                     red
        n/c     RNGo       9
                                4       DTRi    DSRi+DCDi
        RTSo    CTSo       8
                                3       TXDi    RXDi            brown
orng    CTSi    RTSi       7
                                2       RXDo    TXDo            black
        DTRo    DSRo       6
                                1       DCDo    DTRo

Logical RNGi cannot be set with this cable.
Logical DSRi+DCDi cannot be separated with this cable.

References:
:; man ioctl_tty
  https://en.wikipedia.org/wiki/Null_modem
)EoF";

}

#include <cmath>
#include <sstream>
#include <iomanip>      /* for setfill */
#include <string>
#include <fstream>
#include <pthread.h>
#include <unistd.h>     /* for read(), write() */

#include <sys/types.h>  /* for open() */
#include <sys/stat.h>   /* for open() */
#include <fcntl.h>      /* for open() */
#include <string.h>     /* for strerror */
#include <sys/ioctl.h>
#include <linux/serial.h>     /* for serial_icounter_struct */
#include "arg_parser.h"

string strError(int const errnum) {
  char buf[300];
  char* rslt = buf;
#if (_POSIX_C_SOURCE >= 200112L) && !  _GNU_SOURCE
  int sts = strerror_r(errnum, buf, sizeof(buf));
  if (sts) throw logic_error("error in strError");
#else
  rslt = strerror_r(errnum, buf, sizeof(buf));
#endif
  return rslt;
}

struct Timer : public timespec {
  Timer() : timespec{0,0} {}
  Timer& operator-=(Timer const &bbb) {
    if (tv_nsec < bbb.tv_nsec) {
      tv_nsec += 1000000000;
      tv_sec -= 1;
    }
    tv_sec -= bbb.tv_sec;
    tv_nsec -= bbb.tv_nsec;
    return *this;
  }
// works for /small/ increments:
  Timer& operator+=(double const &bbb) {
    tv_nsec += bbb*1.0e9;
    return *this;
  }

  Timer operator-(Timer const &bbb) const {
    Timer tmp = *this;
    tmp -= bbb;
    return tmp;
  }

  operator double() {
    return double(tv_sec) + double(tv_nsec)*1.0e-9;
  }

  string fancy() const {
    stringstream rslt;
    tm tmx;
    memset (&tmx, 0, sizeof (tmx));
    tm * ptr = gmtime_r(&tv_sec, &tmx);
    if (!ptr) throw runtime_error("bad gmtime");
// RFC 2822 : Thu, 21 Oct 2021 07:36:05 +0000
    rslt << put_time(&tmx, "%a, %d %b %Y %H:%M:%S")
        << "." << setfill('0') << setw(9) << tv_nsec
        << " +0000";
    return rslt.str();
  }

  string secs() {
    stringstream rslt;
    rslt << setw(6) << tv_sec
         << "." << setfill('0') << setw(9) << tv_nsec;
    return rslt.str();
  }
};

Timer etime(){
  Timer time;
  static Timer exordium;
  clock_gettime(CLOCK_MONOTONIC, &time);
  if (exordium.tv_sec == 0) exordium = time;
  return time - exordium;
}

string decode(int const serial) {
  string rslt;

  if (serial & TIOCM_DTR) rslt += " DTR";
  else rslt += " dtr";

// "line enable" -- not implemented on DB9
  if (serial & TIOCM_LE) rslt += " LE";
  else rslt += " le";

  if (serial & TIOCM_DSR) rslt += " DSR";
  else rslt += " dsr";

  if (serial & TIOCM_CTS) rslt += " CTS";
  else rslt += " cts";

  if (serial & TIOCM_RTS) rslt += " RTS";
  else rslt += " rts";

  if (serial & TIOCM_CAR) rslt += " DCD";
  else rslt += " dcd";

  if (serial & TIOCM_RNG) rslt += " RNG";
  else rslt += " rng";

  return rslt;
}

void setbit(int const fd, int const mask, int value) {
  int status;
  int rslt;
  rslt = ioctl(fd, TIOCMGET, &status);
  if (rslt < 0) throw invalid_argument("get status failed: " + strError(errno));

  if (value) status |= mask;
  else status &= ~mask;

  rslt = ioctl(fd, TIOCMSET, &status);
  if (rslt < 0) throw invalid_argument("set status failed: " + strError(errno));
}

struct sitcher {
  Timer epoch;
  double delta;         // uncertainty on epoch
  int tty;              // tty file descriptor
  int fd[2];            // pipe file descriptors
  int ival;             // time to snooze in flip mode
  int verbosity;
  string ofile;
  sitcher() : ival(500000), verbosity(0), ofile("-") {}
};

struct messenger {
  int sts;
  Timer time;
#ifdef COUNTEM
  serial_icounter_struct cntr;
  char foobar[100];
#endif
};

// :; sudo setcap CAP_SYS_NICE=ep ./timestamp
// :; sudo getcap ./timestamp
void set_realtime_priority() {
     int ret;

     // We'll operate on the currently running thread.
     pthread_t this_thread = pthread_self();

// Setting thread priority is done through struct sched_param, which
// contains a sched_priority member. It’s possible to query the
// maximum and minimum priorities for a policy.

// struct sched_param is used to store the scheduling priority
     struct sched_param params;

// Set the priority to at most 20:
     int big = sched_get_priority_max(SCHED_FIFO);
     params.sched_priority = min(20, big);

     cout << "About to set realtime priority = " <<
                params.sched_priority << endl;

     ret = pthread_setschedparam(this_thread, SCHED_FIFO, &params);
     if (ret != 0) {
       cout << "Failed to set realtime priority: "
              << strError(errno)
              << endl;
       return;
     }

// Verify policy:
     int policy = 0;

// Verify the change in thread priority
     ret = pthread_getschedparam(this_thread, &policy, &params);
     if (ret != 0) {
       cout << "Couldn't retrieve real-time scheduling paramers" << endl;
     } else {
       if(policy != SCHED_FIFO) {
           cout << "Scheduling is NOT SCHED_FIFO!" << endl;
       } else {
           cout << "Policy is SCHED_FIFO as expected." << endl;
       }
       cout << "Thread priority is " << params.sched_priority << endl;
     }
}


// write status into fd[1]
void *grabber(void* _sitch) {
  sitcher& sitch(*(sitcher*)(_sitch));
  size_t rslt;
  messenger msg;
  size_t ss(sizeof(msg));

  set_realtime_priority();

  while(1){
    msg.time = etime();

    msg.sts = -1;          // in case ioctl bombs out
    rslt = ioctl(sitch.tty, TIOCMGET, &msg.sts);
    if (rslt < 0) throw invalid_argument("get status failed");
    if (msg.sts < 0) throw logic_error("get status bombed out");
#ifdef COUNTEM
    rslt = ioctl(sitch.tty, TIOCGICOUNT, &msg.cntr);
    if (rslt < 0) throw invalid_argument("count failed");
#endif

    rslt = write (sitch.fd[1], &msg, ss);
    if (rslt != ss) throw invalid_argument("write failed");

    int mask = TIOCM_RNG | TIOCM_DSR | TIOCM_CD | TIOCM_CTS;
    rslt = ioctl(sitch.tty, TIOCMIWAIT, &mask);
    if (rslt < 0) throw invalid_argument("wait failed");
  }
}

// read and interpret status
void *saver(void* _sitch) {
  sitcher& sitch(*(sitcher*)(_sitch));
  Timer prev;
  if (sitch.ofile == "") return 0;
  ofstream xxout;
  if (sitch.ofile != "-") {
    xxout.open(sitch.ofile);
  }
  ostream& xout(sitch.ofile != "-" ? xxout : cout);

  xout << "Epoch:, " << sitch.epoch.fancy() << endl;
  xout << "Epoch:, " << sitch.epoch.secs()
        << ",±," << fixed << setprecision(6) << sitch.delta << endl;
  xout << endl;
  xout << endl;

  while(1){
    messenger msg;
    size_t ss(sizeof(msg));
    size_t rslt;

    rslt = read (sitch.fd[0], &msg, ss);
    if (rslt != ss) throw invalid_argument("read failed");
    xout << msg.time.secs()
         << ",  0x"  << hex << msg.sts;

    if (sitch.verbosity) {
      xout << ", " << fixed << setprecision(5) << double(msg.time - prev)
         << ",  " << decode(msg.sts);
    }

    xout << endl;
    prev = msg.time;
  }
}

void snooze(int const interval) {
  timespec now = etime();
  double frac = now.tv_nsec / 1000.;
  double drift = fmod(frac, interval);
  usleep(interval - drift);
}

void *flippy(void* _sitch) {
  sitcher& sitch(*(sitcher*)(_sitch));
  int rslt;
  while (1) {
    usleep(sitch.ival/20.);
    rslt = ioctl(sitch.tty, TIOCCBRK, 0);
    if (rslt < 0) throw invalid_argument("cancel break failed");
    snooze(sitch.ival);
    rslt = ioctl(sitch.tty, TIOCSBRK, 0);
    if (rslt < 0) throw invalid_argument("send break failed");
  }
}

int main(int argc, char * const * argv) {
  string device("/dev/ttyS0");
  int flipmode(0);
  int dtr(0);
  int dsr(0);
  int cts(0);
  int rts(0);
  int le(0);            // "line enable" -- not used
// "local" means ignore modem status DSR and/or DCD
  int local(1);         // bad things happen if not local

  sitcher sitch;
  Timer start2;
  clock_gettime(CLOCK_REALTIME, &sitch.epoch);
  etime();
  clock_gettime(CLOCK_REALTIME, &start2);
  sitch.delta = start2 - sitch.epoch;
  sitch.delta /= 2.0;
  sitch.epoch += sitch.delta;
  arg_parser arg(argc, argv);
  arg.fold_case = 1;
  string progname = arg.nextRaw();

  for (;;) {
    string raw_arg = arg.nextRaw();         // get next keyword
    if (arg.fail()) break;
    if (0) {}
    else if (arg.prefix("-help")) {
      usage();
      exit(0);
    }
    else if (arg.prefix("-pinout")) {
      pinout();
      exit(0);
    }
    else if (arg.prefix("-verbosity")) {
      sitch.verbosity++;
    }
    else if (arg.prefix("-flip")) {
      flipmode++;
    }
    else if (arg.prefix("-device")) {
      arg >> device;
    }
    else if (arg.prefix("-ival")) {
      arg >> sitch.ival;
    }
    else if (arg.prefix("-dtr")) {
      arg >> dtr;
    }
    else if (arg.prefix("-le")) {
      arg >> le;
    }
    else if (arg.prefix("-local")) {
      arg >> local;
    }
    else if (arg.prefix("-dsr")) {
      arg >> dsr;
    }
    else if (arg.prefix("-cts")) {
      arg >> cts;
    }
    else if (arg.prefix("-rts")) {
      arg >> rts;
    }
    else if (arg.prefix("-ofile")) {
      arg >> sitch.ofile;
    }
    else {
      cerr << "Unrecognized: '" << raw_arg << "'" << endl;
      exit(1);
    }
  }

  cout << "Epoch:, " << sitch.epoch.fancy() << endl;
  cout << "Epoch:, " << sitch.epoch.secs()
        << ",±," << setprecision(6) << sitch.delta << endl;

  int rslt;
  sitch.tty = open(device.c_str(), O_RDWR | O_NONBLOCK | O_NOCTTY);
  if (sitch.tty < 0) throw invalid_argument("open failed: " + device);

  int tmp(-99);
  rslt = ioctl(sitch.tty, TIOCGSOFTCAR, &tmp);
  if (rslt < 0) throw invalid_argument("get local failed");
  cout << "tty 'local' flag was previously: " << tmp << endl;
  rslt = ioctl(sitch.tty, TIOCSSOFTCAR, &local);
  if (rslt < 0) throw invalid_argument("set local failed");
  rslt = ioctl(sitch.tty, TIOCSBRK, 0);
  if (rslt < 0) throw invalid_argument("send break failed");

  if (dsr || cts || le)
        cerr << "Beware setting DSR|CTS|LE has no effect AFAICT" << endl;
  setbit(sitch.tty, TIOCM_DTR, dtr);
  setbit(sitch.tty, TIOCM_DSR, dsr);
  setbit(sitch.tty, TIOCM_LE , le);
  setbit(sitch.tty, TIOCM_CTS, cts);
  setbit(sitch.tty, TIOCM_RTS, rts);

  pthread_t threads(0), threadg(0), threadf(0);

  rslt = pipe (sitch.fd);
  if (rslt < 0) throw invalid_argument("pipe failed");

  if (flipmode) {
    pthread_create(&threadf, NULL, flippy, (void*)(&sitch));
  }

  if (flipmode < 2) {
    pthread_create(&threadg, NULL, grabber, (void*)(&sitch));
    pthread_create(&threads, NULL, saver, (void*)(&sitch));
  }

  if(threads) pthread_join(threads, NULL);
  if(threadg) pthread_join(threadg, NULL);
  if(threadf) pthread_join(threadf, NULL);
}