#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <unistd.h>
#include <strings.h>
#include <sys/wait.h>
#include <sys/socket.h>

#include "pline.h"
#include "screen.h"

#include "help.h"

extern const char * const helptext;

/*
 * Write help text to a descriptor.  This assumes the descriptor is one
 *  that supports send(), because we use MSG_NOSIGNAL to avoid needing
 *  to block/ignore SIGPIPE.
 */
static void write_help_text(int fd)
{
 int n;
 int w;
 int o;
 int l;

 o = 0;
 l = strlen(helptext);
 while (1)
  { n = l - o;
    if (n < 1) return;
    w = send(fd,helptext+o,n,MSG_NOSIGNAL);
    if (w < 0)
     { if (errno != EPIPE) pline("Help text write error: %s",strerror(errno));
       return;
     }
    if (w == 0)
     { pline("Help text zero write");
       return;
     }
    o += w;
  }
}

/*
 * Display help.  We fork less(1) with input coming from a pipe to us,
 *  to which we write our help text.
 */
void help(void)
{
 pid_t kid;
 pid_t dead;
 int dp[2];
 int xp[2];
 int e;
 int n;
 int status;

 if (socketpair(AF_LOCAL,SOCK_STREAM,0,&dp[0]) < 0)
  { pline("data socketpair(): %s",strerror(errno));
    return;
  }
 do
  { if (socketpair(AF_LOCAL,SOCK_STREAM,0,&xp[0]) < 0)
     { pline("exec socketpair(): %s",strerror(errno));
       break;
     }
    fcntl(xp[0],F_SETFD,1);
    cleanupscreen();
    do
     { fflush(0);
       kid = fork();
       if (kid < 0)
	{ pline("fork(): %s",strerror(errno));
	  break;
	}
       if (kid == 0)
	{ if (dp[0] != 0)
	   { dup2(dp[0],0);
	     close(dp[0]);
	   }
	  close(dp[1]);
	  close(xp[1]);
	  execlp("less","less",(const char *)0);
	  e = errno;
	  write(xp[0],&e,sizeof(int));
	  _exit(0);
	}
       close(xp[0]);
       xp[0] = -1;
       do
	{ n = recv(xp[1],&e,sizeof(e),MSG_WAITALL);
	  if (n < 0)
	   { pline("exec recv error: %s",strerror(errno));
	     break;
	   }
	  if (n == sizeof(e))
	   { pline("can't exec less: %s",strerror(e));
	     break;
	   }
	  if (n != 0)
	   { pline("exec protocol error: got %d, not %d",n,(int)sizeof(e));
	     break;
	   }
	  close(xp[1]);
	  xp[1] = -1;
	  close(dp[0]);
	  dp[0] = -1;
	  write_help_text(dp[1]);
	  close(dp[1]);
	  dp[1] = -1;
	  while (1)
	   { dead = wait(&status);
	     if (dead < 0)
	      { if (errno == EINTR) continue;
		pline("wait: %s",strerror(errno));
		break;
	      }
	     if (dead != kid) continue;
	     kid = -1;
	     if (WIFEXITED(status))
	      { if (WEXITSTATUS(status) != 0)
		 { pline("less: exit %d",WEXITSTATUS(status));
		 }
	      }
	     else if (WIFSIGNALED(status))
	      { e = WTERMSIG(status);
		if ((e < 1) || (e >= NSIG))
		 { pline("less: signal %d%s",e,WCOREDUMP(status)?" (core dumped)":"");
		 }
		else
		 { pline("less: signal %d [%s]%s",e,sys_signame[e],WCOREDUMP(status)?" (core dumped)":"");
		 }
	      }
	     else
	      { pline("less: incomprehensible status %d",status);
	      }
	     break;
	   }
	} while (0);
       if (kid > 1)
	{ kill(kid,SIGKILL);
	  wait(0);
	}
     } while (0);
    initscreen();
    if (xp[0] >= 0) close(xp[0]);
    if (xp[1] >= 0) close(xp[1]);
  } while (0);
 if (dp[0] >= 0) close(dp[0]);
 if (dp[1] >= 0) close(dp[1]);
}