#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <sys/select.h>
#include <errno.h>

#define BUFL 4096
int fater(char *mes){
  printf("ERROR: %s\n",mes);
  exit(1);
}

void *small(int s){
  void *ret = malloc(s);
  if(!ret)fater("malloc");
  return ret;
}
void write_message(int file,char *mes,int len){
  int written,pos;
  for(pos=0;pos<len;pos+=written){
    written=write(file,mes,len);
    if(written==-1)fater("writing");
  }
}
struct peers{
  int sock;
  struct sockaddr addr;
  socklen_t addrlen;
  struct peers *next;
};

int prepfdset(fd_set *set,struct peers *p,int lstn){
  struct peers *pitr;
  int max=lstn;
  FD_ZERO(set);
  FD_SET(lstn,set);
  for(pitr=p;pitr;pitr=pitr->next){
    FD_SET(pitr->sock,set);
    max=(p->sock>max)?p->sock:max;
  }
  return max+1;
}

int main(int argc,char **argv){
  struct addrinfo hints,*res,*itr;
  int lstn;
  int psock;
  int nfds;
  int fd_changes;
  struct peers *p,*pend,*pitr;
  fd_set rfds;
  unsigned char BUF[BUFL];
  size_t recvd,written;
  char hello[]="ECHO: ";

  /*do lots of busywork*/
  p=NULL;
  pend=NULL;
  pitr=NULL;


  lstn=socket(AF_INET,SOCK_STREAM,IPPROTO_TCP);
  if(lstn==-1)fater("making socket");
  int zero=0;
  if(setsockopt(lstn,SOL_SOCKET,SO_REUSEADDR,&zero,sizeof(int)))fater("setsockopt");

  memset(&hints,0,sizeof(struct addrinfo));
  hints.ai_family=AF_INET;
  hints.ai_socktype=SOCK_STREAM;
  if(getaddrinfo(NULL,"3310",&hints,&res))fater("getaddrinfo");

  for(itr=res;itr;itr=itr->ai_next)
    if(!bind(lstn,itr->ai_addr,itr->ai_addrlen))
      break;
  if(!itr)fater("binding");

  freeaddrinfo(res);
  itr=NULL;

  if(listen(lstn,256))fater("HEY, listen!");

  /*get busy*/
  while(1){
    nfds=prepfdset(&rfds,p,lstn);
    fd_changes=select(nfds,&rfds,NULL,NULL,NULL);
    if(!fd_changes) continue;
    if(fd_changes==-1)
      switch(errno){
        /*when a socket is closed, do we handle it here?*/
        default:fater(strerror(errno));
      }

    /*check the listener for incoming connections*/
    if(FD_ISSET(lstn,&rfds)){
      /*linked list of peer management*/
      if(!pend){
        p=small(sizeof(struct peers));
        pend=p;
      } else {
        pend->next=small(sizeof(struct peers));
        pend=pend->next;
      }
      pend->sock=accept(lstn,&(pend->addr),&(pend->addrlen));
      if(pend->sock==-1)fater("accepting");
      /*is that all the fd_set changes?*/
      if(!--fd_changes) continue;
    }
    /*check peers for incoming messages*/
    for(pitr=p;pitr;pitr=pitr->next){
      if(FD_ISSET(pitr->sock,&rfds)){
        recvd=read(pitr->sock,BUF,BUFL);
        /*do we check for closed sockets here, or in select or wot?*/
        if(recvd==-1)fater("reading socket");
        /*HANDLE input - this changes to make an IRC server*/
        write_message(pitr->sock,hello,strlen(hello));
        write_message(pitr->sock,BUF,recvd);
        /*is that all the fd_set changes?*/
        if(!--fd_changes) break;
      }
    }
  }
}