/**
 * myio.c - Declarations of simple I/O functions.
 *   Based closely on code taken from section 4.3 of K&R.
 *   Error checking removed because error messages should go to client,
 *     not to user.
 */

// +---------+--------------------------------------------------------
// | Headers |
// +---------+

#include <stdio.h>	// For getchar
#include <ctype.h>	// For isdigit, isspace
#include "myio.h"


// +-----------+------------------------------------------------------
// | Constants |
// +-----------+

/**
 * The maximum number of characters we can "unread".
 */
#define BUFSIZE 128


// +---------+--------------------------------------------------------
// | Globals |
// +---------+

/**
 * The buffer in which we store unread characters.
 */
int buf[BUFSIZE];

/**
 * The position in the buffer that stores the most-recently unread
 * character.  (When 0, there is no most-recently unread character.)
 */
int bufp = 0;


// +--------------------+---------------------------------------------
// | Exported Functions |
// +--------------------+

int 
getch ()
{
  return (bufp > 0) ? buf[--bufp] : getchar ();
} // getch

void 
ungetch (int c)
{
  buf[bufp++] = c;
} // ungetch

int
getint (int *pn)
{
  int c;        // The next input character
  int sign;     // The sign of the integer read: Either +1 or -1.

  // Skip over whitespace
  while (isspace (c = getch ()))
    ;

  // Special case: EOF
  if (c == EOF)
    return c;

  // Make sure that we have a valid start to a number
  if ( (! isdigit (c))
       && (c != '+')
       && (c != '-') )
    {
      // We read too far.  Step backwards
      ungetch (c);
      return 0;
    } // if it's not a number

  // Yay!  It's a number.  Get the sign.
  sign = (c == '-') ? -1 : 1;

  // Skip over the sign
  if ( (c == '+') || (c == '-') )
    c = getch ();

  // Read the digits and convert to an integer.  The general algorithm 
  // should be familiar from atoi.
  *pn = 0;
  while (isdigit (c))
    {
      *pn = 10 * *pn + (c - '0');
      c = getch ();
    } // while

  // Incorporate the sign
  *pn *= sign;

  // We stopped because we read one character too far.   Unget that
  // character.  (We don't unget EOF because of a potential flaw in 
  // the design of ungetch.)
  if (c != EOF)
    ungetch (c);

  // We return a special value for EOF
  if (c == EOF)
    return c;

  // And we're done
  return 1;
} // getint