#include <stdio.h>
#include "stackgrowth.h"
#include "frame.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 is_stack_fault (const void *addr, const void *esp);
static bool grow_stack (const void *addr);

/* Determine whether a particular page fault occured due to a stack
   access below the stack pointer that should induce stack growth, and
   if so grow the stack by a single page (capped at MAX_STACK_SIZE). */
bool
handle_stack_fault (const void *ptr, const void *esp)
{
  return is_stack_fault (ptr, esp) && grow_stack (ptr);
}

/* Determines whether a particular page fault appears to be caused by
   a stack access that should induce dynamic stack growth. Stack size
   is capped at MAX_STACK_SIZE. */
static bool
is_stack_fault (const void *addr, const void *esp)
{
  return ((uint32_t*)addr >= ((uint32_t*)esp - MAX_STACK_ACCESS_DIST) &&
          ((PHYS_BASE - pg_round_down (addr)) <= MAX_STACK_SIZE));
}

/* Grows the stack of the process running inside the current thread by a single
   page given a user virtual address inside of the page wherein the new section
   of the stack should be allocated. */
static bool
grow_stack (const void *addr)
{
  struct thread *t = thread_current ();
  void *last_page = pg_round_down (addr);

  /* This function should only be called when dealing with a faulting stack
     access that induces stack growth, so the provided address shouldn't be
     present in a page within the current thread's page directory. */
  ASSERT (pagedir_get_page (t->pagedir, last_page) == NULL);

  uint8_t *new_page = frame_alloc (PAL_ZERO, last_page, t);
  if (new_page == NULL)
    return false;

  if (!pagedir_set_page (t->pagedir, last_page, new_page, true))
  {
    frame_free (new_page);
    return false;
  }

  return true;
}