#include <asm/system.h>
#include <kernel/memory.h>
#include <stdint.h>
#include <sys/types.h>

static char __attribute__((aligned (4096))) mapped_page[4096];

static char map[NPAGES / 8];

static pdir_t kpdir;

ptab_t ktab;

void *alloc_physical_page(void) {
  int i, j;

  for(i = 32; i < sizeof(map); i++) {
    if(map[i] == -1)
      continue;

    for(j = 0; j < 8; j++) {
      if(!((map[i] >> j) & 1))
        break;
    }

    map[i] |= 1 << j;
    return (void*) (((i << 3) + j) << 12);
  }

  return NULL;
}

int free_physical_page(void *page) {
  char tmp;
  uint32_t p = (uint32_t) page >> 12;

  if(p > NPAGES)
    return -1;

  tmp = map[p >> 3];
  map[p >> 3] &= ~(1 << (p & 7));

  if((tmp & (1 << (p & 7))))
    return 0;

  return -1;
}

void *alloc_physical_pages(unsigned int n) {
  void *p = NULL;
  void *last = NULL;
  void **page;

  while(n--) {
    p = alloc_physical_page();
    if(p == NULL) {
      page = &last;
      while(*page) {
	free_physical_page(*page);
        page = *page;
      }
      return NULL;
    }

    map_page(p);
    *((void**) mapped_page) = last;
    last = p;
  }

  return p;
}

void *map_page(void *page) {
  uint32_t p = (uint32_t) mapped_page;

  /* enforce 4KB page alignment */
  page = (void*) ((uint32_t) page & ~0xFFF);

  ktab[(p >> 12) & 0x3FF] = (uint32_t) page | 0x003;

  invlpg(mapped_page);

  return mapped_page;
}

void paging_init(void) {
  int i;

  /* empty the page directory */
  for(i = 0; i < PGENT; i++)
    kpdir[i] = 0;

  /* populate the kernel's page table */
  for(i = 0; i < PGENT; i++) {
    ktab[i] = 0;
    if(i < 256)
      ktab[i] = (i << 12) | 0x003;
  }

  /* populate the kernel's page directory */
  kpdir[0] = ((pde_t) ktab) | 0x007;

  __asm__ (
      "mov %%eax, %%cr3\n"
      "mov %%cr0, %%eax\n"
      "or $0x80000000, %%eax\n"
      "mov %%eax, %%cr0\n"
      :: "a" (&kpdir)
      );
}