#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <signal.h>


// need a command loop that accepts three commands:
//  1) list 2) forkoff 3) exit
// fork off children, maintain a list of children, kill children on exit

//need a list of children

#define MAX_CHILDREN         5
#define MAX_LINE_LENGTH    256

pid_t kids[MAX_CHILDREN];

void    insert_child(pid_t);
void    cleanup_children(void);
void    do_work(void);
void    print_children(void);

int highest_unused = 0;

/**
 * Iterate over list of children, kill them
 //signal child to SIGINT
 //waitpid?
 */
void cleanup_children()
{
  int i = 0;

  for(i=0;i<highest_unused;i++) {
    fprintf(stdout, "killing child %d\n", kids[i]);
    kill(kids[i], SIGINT);
  }
}

void insert_child(pid_t p)
{
  if(highest_unused < MAX_CHILDREN) {
    fprintf(stdout, "\nadding %d to child list\n", p);
    kids[highest_unused] = p;
    highest_unused++;
  } else {
    fprintf(stdout, "cannot add a child; storage full\n");
    return;
  }
}

void print_children()
{
  int i = 0;

  for(i=0; i < highest_unused; i++) {
    fprintf(stdout, "child: %d\n", kids[i]);
  }
}


/**
 * Need to;
 *  fork off children
 *  store child pids via add_child()
 *  test for errors (test return value of fork)
 *  need a command interpreter loop
 */
void do_work()
{
  char* line = NULL;
  pid_t pid = 0;

  line = (char*) calloc(MAX_LINE_LENGTH+1, sizeof(char));

  if(NULL==line) {
    fprintf(stderr, "sorry, could not allocate space for cmd interpreter\n");
    exit(-1);
  }

  for(;;)
  {
    fprintf(stdout, "parent> ");
    
    fscanf(stdin, "%s", line);
    line[MAX_LINE_LENGTH]='\0';

    if (0==strncmp("list",line,4)) {
      print_children();
    } else if(0==strncmp("forkoff",line,7)) {
      if(highest_unused >= MAX_CHILDREN) {
	fprintf(stdout, "too many kids, not forking\n");
	continue;
      }

      pid = fork();

      if(0==pid) { //child is executing here
	while ( 1 ) { 
          sleep(2); 
        }
      } else if ( pid < 0 ) { //error, could not fork
	fprintf(stderr, "could not fork\n");
      } else { //parent is executing here
	insert_child(pid);
      }

    } else if (0==strncmp("\0",line,1)) {
      return;
    } else if (0==strncmp("exit",line,4)) {
      return;
    } else {
      fprintf(stderr, "unknown command\n");
    }
  }

  free(line);
  line=NULL;
}

int main(int argc, char* argv[])
{
  do_work();
  cleanup_children();
  return 0;
}