#include <stdio.h>
#include "stackgrowth.h"
#include "threads/palloc.h"
#include "threads/thread.h"
#include "threads/vaddr.h"
#include "userprog/pagedir.h"

#define MAX_STACK_ACCESS_DIST 32

static bool needs_new_page (const void *addr, const void *esp);
static bool grow_stack (const void *addr);

bool
try_alloc_new_page (const void *ptr, const void *esp)
{
  if (needs_new_page (ptr, esp))
  {
    if (!grow_stack (ptr))
      return 0;
    else
      return 1;
  }
  else
    return 0;
}

/* Validates a given address for being a stack query and not a generic erroneous
   address
 */
static bool
needs_new_page (const void *addr, const void *esp)
{
    return (is_user_vaddr (addr) &&
            (uint32_t*)addr >= ((uint32_t*)esp - MAX_STACK_ACCESS_DIST) &&
            ((PHYS_BASE - pg_round_down (addr))
                          <= MAX_STACK_SIZE));
}

/* Extends the stack by the necessary number of pages */
static bool
grow_stack (const void *addr)
{
  struct thread *t = thread_current ();
  void *last_page = pg_round_down (addr);

  uint8_t *new_page = palloc_get_page (PAL_USER | PAL_ZERO);
  if ( new_page == NULL)
    return false;

  bool added_page = pagedir_get_page (t->pagedir, last_page) == NULL
                    && pagedir_set_page (t->pagedir, last_page, new_page, true);

  if (!added_page) {
    palloc_free_page (new_page);
    return false;
  }
  return true;
}