#include <fcntl.h>
#include <signal.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

extern int errno;

#define PAUSE sleep(60)

void errmsg(const char* m)
{
  write(2, m, strlen(m));
}

void warn_sys(const char* m)
{
  errmsg("qfilelog: warning: ");
  errmsg(m);
  errmsg(": ");
  errmsg(strerror(errno));
  errmsg("\n");
}

void warn(const char* m)
{
  errmsg("qfilelog: warning: ");
  errmsg(m);
  errmsg(".\n");
}

void fatal(const char* m)
{
  errmsg("qfilelog: fatal error: ");
  errmsg(m);
  errmsg("\n");
  exit(1);
}

#define BUFSIZE 4096
static int fd;
static char* filename;
static char buf[BUFSIZE];

ssize_t do_read(void)
{
  ssize_t rd = read(0, buf, BUFSIZE);
  if(rd == -1)
    rd = 0;
  return rd;
}

void do_write(ssize_t rd)
{
  ssize_t offset = 0;
  ssize_t wr;
  while(offset < rd) {
    wr = write(fd, buf+offset, rd-offset);
    if(wr == -1) {
      warn_sys("Can't write, pausing");
      PAUSE;
    }
    else
      offset += wr;
  }
}

void do_close(void)
{
  if(fd >= 0) {
    while(fsync(fd) == -1) {
      warn_sys("Error syncing the file, pausing");
      PAUSE;
    }
    while(close(fd) == -1) {
      warn_sys("Error closing the file, pausing");
      PAUSE;
    }
  }
}

void do_open(void)
{
  do {
    fd = open(filename, O_WRONLY|O_CREAT|O_APPEND, 0666);
    if(fd == -1) {
      warn_sys("Error opening the output file, pausing");
      PAUSE;
    }
  } while(fd == -1);
}

void loop(void)
{
  ssize_t rd;
  for(;;) {
    rd = do_read();
    if(rd)
      do_write(rd);
  }
}

void catch_hup(int flag)
{
  signal(SIGHUP, catch_hup);
  do_close();
  do_open();
}

void catch_int(int flag)
{
  do_close();
  exit(0);
}

int main(int argc, char* argv[]) 
{
  if(argc < 2) {
    fatal("usage: filelog filename\n");
    return 1;
  }
  filename = argv[1];
  signal(SIGHUP, catch_hup);
  signal(SIGINT, catch_int);
  signal(SIGTERM, catch_int);
  fd = -1;
  do_open();
  loop();
  return 0;			/* Never reached! */
}