#define ATS_DYNLOADFLAG 0

#include "kernel/prelude/kernel_prelude.hats"

staload "./table.sats"
staload "./entry.sats" 

staload "lib/SATS/valid.sats"
staload "lib/DATS/valid.dats"

assume table_t(c:int) = tablePtr1 c


// Calculate table address of next table based on current table and index: P4->P3->P2->P1
fn next_table_address{n:int|n < 3}(table : !table_t(n), index : sizeLt(ENTRY_COUNT)):<> Valid Ptr1 = let
  val entry = table_get_at(table,index)
in
  if (contains_flag(entry,PRESENT) && ~contains_flag(entry,HUGE_PAGE)) then
    let 
      val next = g1ofg0((Ptr1_to_sz(table.3) << 9) lor (index << 12))
    in
      if next > i2sz(0) then
        create_valid(sz_to_Ptr1(next))
      else
        create_unvalid()
    end
  else
    create_unvalid()
end

// Checks if next table exists and returns bool
fn next_table_exists{n:int|n < 3}(table: !table_t(n),index : sizeLt(ENTRY_COUNT)):<> bool = let
  val vnext = next_table_address(table,index)
in
  if is_valid(vnext) then
    let val _ = unwrap_valid(vnext) in true end
  else 
    (destroy_unvalid(vnext); false)
end

implement table_get_at(table,i) = let
  val entry = (table.3->[i]) : entry_t
in
  entry
end

implement table_set_at(table,i,x) = table.3->[i] := x

// Set all the entries in the table to unused (zero)
fn set_zero(table: &Table_t):<!wrt> void = let 
  fun loop{i:nat | i < ENTRY_COUNT}.<ENTRY_COUNT-i>.(i : size_t i,t : !Table_t):<!wrt> void = let 
  in
    set_unused(t.3->[i]);
    if i < ENTRY_COUNT - 1 then
      loop(succ(i),t)
  end
in
  loop(i2sz(0),table)
end

// UNSAFE: unsafe block
local

  staload UN = "prelude/SATS/unsafe.sats"

in

  // TODO: define safe unique ownership for this table
  // see https://os.phil-opp.com/page-tables/#safety-2
  implement get_P4() =  let
    val (pf,fpf | p) = $UN.ptr_vtake(ulint_to_Ptr1(0xfffffffffffff000ul))
  in
    (pf,fpf,0u | p)
  end

  implement next_table(table,index) = let
    val next = next_table_address(table,index)
    prval level = table.2
  in
    consume(table);
    if is_valid(next) then 
      let
        val t = unwrap_valid(next)
        val (pf, fpf | p) = $UN.ptr_vtake(t)
      in
       create_valid ((pf,fpf, succ(level) | p))
      end
    else
      let
        val () = destroy_unvalid(next)
      in
        create_unvalid();
      end
  end

  implement next_table_create(table,index) = let
    staload "kernel/memory/frame.sats"
  in
    if ~next_table_exists(table,index) then (
      println!("not exists");
      assertloc(~contains_flag(table[index],HUGE_PAGE));
      table[index] := create_entry(allocate_frame(),flags,i2sz(2)) where {
        var flags = @[entry_flag](PRESENT,WRITABLE)
      };
      let 
        val vnext = next_table(table,index)
      in
        if is_valid(vnext) then
            let var next = unwrap_valid(vnext) in (set_zero(next); create_valid(next)) end
        else (
          destroy_unvalid(vnext);
          create_unvalid()
        )
      end
    ) else 
      $UN.castvwtp0(next_table(table,index)) //This is safe
  end

end