#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h> 
#include <sys/socket.h> 
#include <netinet/in.h> 
#include <netdb.h>
#include <arpa/inet.h>

//  on demand scheduling of tasks to workers
//  receive request from worker i -> send task to compute to worker i
//  when no more tasks are available, send an EOS termination 
// 
//  usage is: 
//     a.out portno 
//           number of the port used to get worker task requests

#define MAXHOSTNAME 80

int main(int argc, char * argv[]) {
        int s,si, retcode, i;
        unsigned int salen; 
        struct sockaddr_in sa,sai;
        char hostname[MAXHOSTNAME];

        int task = 0;           // tasks are positive integeres, in this case
        int tasklimit = 100;    // we'll send tasklimit tasks before stopping
        int eos = -1;           // special task to denote End Of Stream

        // code needed to set up the communication infrastructure
        printf("Declaring socket\n");
        si = socket(AF_INET,SOCK_STREAM,0);     // socket for inputs
        if(si == -1) {perror("opening socket for input"); return -1;}
        sai.sin_family = AF_INET;
        sai.sin_port = htons(atoi(argv[1]));
        gethostname(hostname,MAXHOSTNAME);
        memcpy(&sai.sin_addr, (gethostbyname(hostname)->h_addr), 
                sizeof(sa.sin_addr));
        printf("Binding to %s\n",inet_ntoa(sai.sin_addr));
        retcode = bind(si,(struct sockaddr *) & sai, sizeof(sai));
        if(retcode == -1) {
                perror("while calling bind"); return -1; }
        printf("Listening socket\n");
        retcode = listen(si,1); 
        if(retcode == -1) { 
                perror("while calling listen"); return -1; }

        while(1==1) {
          salen = sizeof(sa);
          printf("Accepting connections .... \n");
          s = accept(si,(struct sockaddr *)&sa,&salen);  // accept a connection
          if(s == 1) {
                  perror("while calling an accept"); return -1; }
          retcode = read(s,&i,sizeof(int));  // read request from worker 
          if(retcode == -1) {
                  perror("while reading task from worker"); return -1; }
          printf("%d ",i); fflush(stdout);
          if(task < tasklimit) {  // send a task to the requesting worker
                  write(s,&task,sizeof(task));
                  printf("sent task %d to worker %d\n",task,i);
                  task++;       // next task to be sent 
          } else { // if no more tasks, then send an EOS
                  write(s,&eos,sizeof(task));
                  printf("Send EOS to worker %d\n",i);
          }
          close(s);
        }
        printf("Closing operations\n");
        return 0; 
}