#include <string>
#include <iostream>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <cstdlib>
#include <vector>
#include <ctime>

void usage() 
{
  fprintf(stderr,"ioverify <path> <nfiles> <nverify>\n");
  fprintf(stderr," example: ioverify /var/tmp/ 2048 0    # creates 2048 1MB test pattern files under /var/tmp/\n");
  fprintf(stderr,"          ioverify /var/tmp/ 2048 1000 # runs 1000 random verifications on all 2048 files under /var/tmp/\n");
  exit(-1);
}

int main(int argc , char* argv[])
{
  int retc=0;
  if (argc != 4) {
    usage();
  }
  
  std::string prefix = argv[1];
  size_t nfiles = std::strtol(argv[2],0,10);
  size_t nverify = std::strtol(argv[3],0,10);
  fprintf(stderr,"running: prefix=%s nfiles=%lu nverify=%lu\n", 
	  prefix.c_str(), 
	  nfiles,
	  nverify);

  if (nverify == 0) {
    // this is the creation of pattern files

    for (size_t n = 0; n < nfiles; n++) {
      unsigned char buffer[64*1024];
      for (size_t i =0; i< 65536; ++i) {
	buffer[i] = (n+i)%256;
      }

      std::string path = prefix;
      path += "/pattern.";
      path += std::to_string(n);
      int fd = creat(path.c_str(), S_IRWXU);
      if (fd>0) {
	for (size_t l=0; l< 16; l++) {
	  ssize_t nwr = write(fd, buffer, 64*1024);
	  if (nwr != 64*1024) {
	    fprintf(stderr,"error: failed to write loop=%lu nrw=%ld\n", l, nwr);
	    exit(-1);
	  }
	}
	close(fd);
	fprintf(stderr,"ok: wrote pattern file path='%s' pattern-tpe=%lu\n", path.c_str(), n);
      } else {
	fprintf(stderr,"error: failed to create path='%s' errno=%d\n",path.c_str(), errno);
	exit(-1);
      }
    }
  } else {
    std::srand(std::time(nullptr));

    std::vector<int> fds;
    for (size_t i = 0; i < nfiles; i++) {
      std::string path = prefix;
      path += "/pattern.";
      path += std::to_string(i);
      
      fds.push_back(open(path.c_str(), 0));
      if (fds[i] <1) {
	fprintf(stderr,"error: open failed for path='%s' errno=%d\n", path.c_str(), errno);
	retc = -1;
      }
    }

    
    for (size_t v = 0 ; v < nverify; v++) {
      for (size_t i = 0; i < nfiles; i++) {
	size_t size = std::rand() % (1024);
	off_t offset = std::rand() % ((1024*1024) - size);

	unsigned char buffer[1024];
	size_t nr = pread(fds[i], buffer, size, offset);
	if (nr != size) {
	  fprintf(stderr,"error: failed to read file=%lu offset=%lu size=%lu read=%lu\n", i, offset, size, nr);
	  retc = -1;
	}
	// verify pattern
	for (size_t l = 0; l < size; l++) {
	  if (buffer[l] != ((offset+l+i)%256)) {
	    fprintf(stderr,"error: pattern for file=%lu offset=%lu should be %x but we got %x\n", i, offset+l, (unsigned int) (offset+l+i)%256, buffer[l]);
	    retc = -1;
	  }
	}
      }
    }
    for (size_t i = 0; i < nfiles; i++) {
      close(fds[i]);
    }
  }
  exit(retc);
}