#include<sys/param.h>
#include<stdio.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<stdlib.h>
#include<string.h>
#define MAXPLAN 20
#define DELIMITER "\n---8<---\n"

char host[MAXHOSTNAMELEN+1];
char path[MAXPATHLEN];
int planpos[MAXPLAN];

char *programname;
void emsg();

int main(argc,argv)
int argc;
char **argv;
{
   FILE *fp;
   char *plandata;
   int planno;
   char *hostdata;
   char *home;
   char *ptr,*p;
   char *logdata;
   struct stat st;
   int len;
   int flg=0;
   int i;
   int last;
   programname=argv[0];  /* for error messages */
   if((ptr=strrchr(programname,'/')))programname=ptr+1;
   /* the following lines set flg to 1 on login, 2 on logout. */
   if(argc>1&&!(argc==2&&((strstr(argv[1],"login")&&(flg=1))||
         (strstr(argv[1],"logout")&&(flg=2))))){
      fprintf(stderr,"Usage: %s [login|logout]\n",programname);
      exit(1);
   }
   if(gethostname(host,sizeof host))emsg("gethostname");
   if(!(home=getenv("HOME"))){
      fprintf(stderr,"%s: HOME: undefined environment variable\n",programname);
      exit(1);
   }
   sprintf(path,"%s/.plans",home);
   if(stat(path,&st))planno=0;
   else{ /* slurp in the whole .plans file, and separate it into sections */
      if(!(plandata=malloc((size_t)st.st_size+1)))emsg("malloc");
      if(!(fp=fopen(path,"r")))emsg(path);
      if((len=fread(plandata,1,(int)st.st_size,fp))!=st.st_size){
         fprintf(stderr,"%s: %s: read error\n",programname,path);
         exit(1);
      }
      fclose(fp);
      plandata[len]=0;
      planpos[0]=0;
      for(planno=1,ptr=plandata;(ptr=strstr(ptr,DELIMITER));
         planpos[planno++]=(ptr+=sizeof DELIMITER-1)-plandata)ptr[1]=0;
   }
   /* allocate memory and read in the .logins file. There will be some extra
      allocated space to store another host name, in case of a login.     */
   sprintf(path,"%s/.logins",home);
   if(stat(path,&st)){
      if(!(hostdata=malloc((size_t)MAXHOSTNAMELEN+2)))
         emsg("malloc");
      hostdata[len=0]=0;
   }
   else{
      if(!(hostdata=malloc((size_t)st.st_size+MAXHOSTNAMELEN+2)))
         emsg("malloc");
      if(!(fp=fopen(path,"r")))emsg(path);
      if((len=fread(hostdata,1,(int)st.st_size,fp))!=st.st_size){
         fprintf(stderr,"%s: %s: read error\n",programname,path);
         exit(1);
      }
      fclose(fp);
      hostdata[len]=0;
   }
   switch(flg){
   case 1: if(len)hostdata[len++]=' ';     /* add host name */
           strcpy(hostdata+len,host);
           break;
   case 2: if((ptr=strstr(hostdata,host))) /* delete host name */
              if(!ptr[i=strlen(host)])ptr[-(ptr>hostdata)]=0;
              else for(i++;(ptr[0]=ptr[i]);ptr++);
/* default: do nothing */
   }
   if(flg){ /* write the new .logins, or remove if it is empty */
      if(!(len=strlen(hostdata)))
         if(unlink(path))emsg(path);
         else;
      else {
         if(!(fp=fopen(path,"w")))emsg(path);
         if(fwrite(hostdata,1,len,fp)!=len)emsg(path);
         fclose(fp);
      }
   }
   /* Write a plan to the .plans file; free plan storage */
   sprintf(path,"%s/.plan",home);
   if(!(fp=fopen(path,"w")))emsg(path);
   if(planno){
      i=getpid()%planno;
      len=strlen(ptr=plandata+planpos[i]);
      if(fwrite(ptr,1,len,fp)!=len)emsg(path);
      free(plandata);
   }
   else fputs("No plan.\n",fp);
   /* if there are logins, construct the list, avoiding repetitions */
   if((ptr=hostdata)[0]){
      if(!(logdata=malloc((size_t)strlen(hostdata)+50)))
         emsg("malloc");
      strcpy(logdata,"\nCurrently logged on at:");
      last=0;
      while(!last){
         if(!(p=strchr(ptr,' ')))p=strchr(ptr,0),last=1;
         *p=0;
         if(last||!strstr(p+1,ptr))
            strcat(logdata," "),
            strcat(logdata,ptr);
         ptr=p+1;
      }
      ptr=logdata;
      /* add the list to the plan, splitting up long lines */
      while(strlen(ptr)>72){
         for(p=ptr+72;*--p!=' ';);
         *p=0;
         fprintf(fp,"%s\n",ptr);
         ptr=p+1;
      }
      fprintf(fp,"%s\n",ptr);
      free(logdata);
   }
   fclose(fp);
   free(hostdata);
   return 0;
}
         
void emsg(data)
char *data;
{
   extern int errno;
   int e=errno;
   fprintf(stderr,"%s: ",programname);
   errno=e; /* just in case printf spoiled the error number */
   perror(data);
   exit(1);
}