// +==============================================+
// |    HEADERS                                   |
// +===================================== cta os =+
#include "mmngr_vi.h"
#include "mmngr_ph.h"

// +==============================================+
// |    DEFINITIONS                               |
// +===================================== cta os =+
#define PAGE_SIZE 4096
#define PTABLE_ADDR_SPACE_SIZE 0x400000
#define DTABLE_ADDR_SPACE_SIZE 0xffffffff

pdirectory* _current_directory;
unsigned _current_page_directory_base_register;
extern unsigned char *memset (unsigned char *dest, unsigned char val, int count);
extern char getch();

// +==============================================+
// |    PAGE FUNCTIONS                            |
// +===================================== cta os =+
unsigned char vmmngr_alloc_page (pt_entry* entry)
{
      void* p = pmmngr_alloc_block ();
      if (!p) return 0;
      
      pt_entry_set_frame(entry, (unsigned)p);
      pt_entry_add_attrib (entry, _I86_PTE_PRESENT);
      
      return 1;
}

void vmmngr_free_page (pt_entry* entry)
{
      void* p = (void*) pt_entry_get_frame(*entry);
      
      if (p) pmmngr_free_block (p);
      
      pt_entry_del_attrib (entry, _I86_PTE_PRESENT);
}


// +==============================================+
// |    PAGE TABLE FUNCTIONS                      |
// +===================================== cta os =+
inline void vmmngr_ptable_clear(ptable* p)
{
      if(p) memset ((unsigned char*)p, 0, sizeof(ptable));
}

inline unsigned vmmngr_ptable_virt_to_index (unsigned addr)
{
      return (addr >= PTABLE_ADDR_SPACE_SIZE) ? 0 : addr/PAGE_SIZE;
}

inline pt_entry* vmmngr_ptable_lookup_entry (ptable* p, unsigned addr)
{
      if (p) return &p->m_entries[vmmngr_ptable_virt_to_index(addr)];
      return 0;
}


// +==============================================+
// |    PAGE DIRECTORY FUNCTIONS                  |
// +===================================== cta os =+
inline void vmmngr_pdirectory_clear(pdirectory* dir)
{
      if(dir) memset ((unsigned char*)dir, 0, sizeof(pdirectory));
}

inline unsigned vmmngr_pdirectory_virt_to_index (unsigned addr)
{
      return (addr > DTABLE_ADDR_SPACE_SIZE) ? 0 : addr/PAGE_SIZE;
}

inline pd_entry* vmmngr_pdirectory_lookup_entry (pdirectory* dir, unsigned addr)
{
      if (dir) return &dir->m_entries[vmmngr_ptable_virt_to_index(addr)];
      return 0;
}

// +==============================================+
// |    VIRTUAL MEMORY MANAGER                    |
// +===================================== cta os =+
inline unsigned char vmmngr_switch_pdirectory (pdirectory* dir)
{
      if (!dir) return 0;
      _current_directory = dir;
      
      write_cr3 (_current_page_directory_base_register);
      return 1;
}

pdirectory* vmmngr_get_directory() {
    return _current_directory;
}

void vmmngr_initialize()
{
      // Allocate default page table
      ptable* table = (ptable*) pmmngr_alloc_block();
      if (!table) return;
      
      // Clear page table
      vmmngr_ptable_clear(table);
      
      // Identity map the first page table
      int i, frame;
      for (i = 0, frame = 0; i < 1024; i++, frame += 4096)
      {
            // Create a new page
            pt_entry page = 0;
            pt_entry_add_attrib (&page, _I86_PTE_PRESENT);
            pt_entry_set_frame (&page, frame);
            
            table->m_entries[vmmngr_ptable_virt_to_index(frame)] = page;
      }

      // Create default directory table
      pdirectory* dir = (pdirectory*) pmmngr_alloc_blocks(3);
      if (!dir) return;

      // Clear directory table and set it as current
      vmmngr_pdirectory_clear(dir);

      // Get first entry in dir table and set it up to point to our table
      pd_entry* entry = vmmngr_pdirectory_lookup_entry(dir, 0);
      pd_entry_add_attrib (entry, _I86_PDE_PRESENT);
      pd_entry_add_attrib (entry, _I86_PDE_WRITABLE);
      pd_entry_set_frame (entry, (unsigned) table);
 
      // Store current PDBR
      _current_page_directory_base_register = (unsigned) &dir->m_entries;

      // Switch to our page directory
      vmmngr_switch_pdirectory (dir);
      
      // Enable paging
      pmmngr_paging_enable (1);
}