-- Derived from GRUB  --  GRand Unified Bootloader
-- Copyright (C) 1999, 2001, 2003  Free Software Foundation, Inc.
-- Copyright (C) 2023 secunet Security Networks AG
--
-- This program is free software; you can redistribute it and/or modify
-- it under the terms of the GNU General Public License as published by
-- the Free Software Foundation; either version 2 of the License, or
-- (at your option) any later version.

with System;
with Interfaces;
with Interfaces.C;
with Interfaces.C.Strings;

with FILO.Blockdev;
with FILO.FS.VFS;

use Interfaces.C;

package body FILO.FS.Ext2 is

   function Is_Mounted (State : T) return Boolean is (State.S >= Mounted);
   function Is_Open (State : T) return Boolean is (State.S = File_Opened);

   --------------------------------------------------------------------------

   SUPERBLOCK_SIZE            : constant := 1024;
   SUPERBLOCK_BLOCKS          : constant := SUPERBLOCK_SIZE / BLOCK_SIZE;

   SUPERBLOCK_MAGIC           : constant := 16#ef53#;
   OLD_REV                    : constant := 0;
   DYNAMIC_REV                : constant := 1;
   FEATURE_INCOMPAT_EXTENTS   : constant := 16#0040#;
   FEATURE_INCOMPAT_64BIT     : constant := 16#0080#;

   procedure Mount
     (State    : in out T;
      Part_Len : in     Partition_Length;
      Success  :    out Boolean)
   is
      Super_Block : Buffer_Type (0 .. SUPERBLOCK_SIZE - 1) := (others => 0);
   begin
      if Part_Len < 2 * SUPERBLOCK_SIZE then
         Success := False;
         return;
      end if;

      Blockdev.Read (Super_Block, 1 * SUPERBLOCK_SIZE, Success);
      if not Success then
         return;
      end if;

      if Read_LE16 (Super_Block, 14 * 4) /= 16#ef53# then
         Success := False;
         return;
      end if;

      State.Part_Len := Part_Len;
      State.First_Data_Block := Block_Offset (Read_LE32 (Super_Block, 5 * 4));

      declare
         S_Log_Block_Size : constant Unsigned_32 := Read_LE32 (Super_Block, 6 * 4);
      begin
         if S_Log_Block_Size <= Unsigned_32 (Log_Block_Size'Last - 10) then
            State.Block_Size_Bits := Log_Block_Size (S_Log_Block_Size + 10);
         else
            Success := False;
            return;
         end if;
      end;

      declare
         S_Inodes_Per_Group : constant Unsigned_32 := Read_LE32 (Super_Block, 10 * 4);
      begin
         if S_Inodes_Per_Group in 1 .. Unsigned_32 (Positive'Last) then
            State.Inodes_Per_Group := Positive (S_Inodes_Per_Group);
         else
            Success := False;
            return;
         end if;
      end;

      declare
         S_Rev_Level : constant Unsigned_32 := Read_LE32 (Super_Block, 19 * 4);
      begin
         if S_Rev_Level >= DYNAMIC_REV then
            declare
               S_Inode_Size : constant Unsigned_16 := Read_LE16 (Super_Block, 22 * 4);
            begin
               if S_Inode_Size in
                  Unsigned_16 (Inode_Size'First) .. Unsigned_16 (Inode_Size'Last)
               then
                  State.Inode_Size := Inode_Size (S_Inode_Size);
               else
                  Success := False;
                  return;
               end if;
            end;
         else
            State.Inode_Size := Inode_Size'First;
         end if;
      end;

      declare
         S_Feature_Incompat : constant Unsigned_32 := Read_LE32 (Super_Block, 24 * 4);
      begin
         State.Feature_Extents := (S_Feature_Incompat and FEATURE_INCOMPAT_EXTENTS) /= 0;
         State.Feature_64Bit     := (S_Feature_Incompat and FEATURE_INCOMPAT_64BIT) /= 0;
         if State.Feature_64Bit then
            declare
               S_Desc_Size : constant Unsigned_16 := Read_LE16 (Super_Block, 63 * 4 + 2);
            begin
               if S_Desc_Size in
                  Unsigned_16 (Desc_Size'First) .. Unsigned_16 (Desc_Size'Last)
               then
                  State.Desc_Size := Desc_Size (S_Desc_Size);
               else
                  Success := False;
                  return;
               end if;
            end;
         else
            State.Desc_Size := Desc_Size'First;
         end if;
      end;

      State.S := Mounted;
   end Mount;

   procedure Read_FSBlock
     (State    : in     T;
      Buf      :    out Buffer_Type;
      FSBlock  : in     FSBlock_Offset;
      Success  :    out Boolean)
   with
      Pre =>
         Is_Mounted (State) and
         Buf'Length = 2 ** State.Block_Size_Bits
   is
      Block_Size : constant Blockdev_Length := 2 ** State.Block_Size_Bits;
      Max_Block_Offset : constant FSBlock_Offset :=
         FSBlock_Offset (State.Part_Len / Block_Size - 1);
   begin
      if FSBlock > Max_Block_Offset then
         Success := False;
         return;
      end if;
      Blockdev.Read (Buf, Blockdev_Length (FSBlock) * Block_Size, Success);
   end Read_FSBlock;

   procedure Ext2_Block_Map
     (State       : in out T;
      Logical     : in     FSBlock_Logical;
      Physical    :    out FSBlock_Offset;
      Success     :    out Boolean)
   is
      Block_Size : constant Natural := 2 ** State.Block_Size_Bits;
      Addr_Per_Block : constant FSBlock_Logical := FSBlock_Logical (Block_Size / 4);
      Max_Addr_Per_Block : constant FSBlock_Logical := FSBlock_Logical (2 ** Log_Block_Size'Last / 4);
      type Addr_In_Block_Range is range 0 .. Max_Addr_Per_Block - 1;

      procedure Indirect_Block_Lookup
        (Indirect_Block_Phys  : in     FSBlock_Offset;
         Addr_In_Block        : in     Addr_In_Block_Range;
         Level                : in     Block_Cache_Index;
         Logical_Off          : in     FSBlock_Logical;
         Next_Physical        :    out FSBlock_Offset;
         Success              :    out Boolean)
      with
         Pre => FSBlock_Logical (Addr_In_Block) < Addr_Per_Block
      is
         -- Limit cache usage in case of incredibly huge block size:
         Cache_Level : constant Block_Cache_Index :=
           (if    State.Block_Size_Bits > 15                   then Any
            elsif State.Block_Size_Bits > 14 and Level > Any   then Last_Level
                                                               else Level);
         Cache_Index : constant Index_Type :=
            Block_Cache_Index'Pos (Cache_Level) * Block_Size;
         Cache_End : constant Index_Type := Cache_Index + Block_Size - 1;
      begin
         if State.Block_Cache_Index (Cache_Level) /= Logical_Off then
            Read_FSBlock
              (State    => State,
               Buf      => State.Block_Cache (Cache_Index .. Cache_End),
               FSBlock  => Indirect_Block_Phys,
               Success  => Success);
            State.Block_Cache_Index (Cache_Level) := Logical_Off;
            if not Success then
               return;
            end if;
         end if;

         Next_Physical := FSBlock_Offset (Read_LE32
           (Buf => State.Block_Cache (Cache_Index .. Cache_End),
            Off => Natural (Addr_In_Block) * 4));
         Success := True;
      end Indirect_Block_Lookup;

      Logical_Rest : FSBlock_Logical := Logical;
   begin
      if Logical_Rest < Direct_Blocks then
         Physical := FSBlock_Offset (State.Direct_Blocks (Natural (Logical)));
         Success := True;
         return;
      end if;

      Logical_Rest := Logical_Rest - Direct_Blocks;
      if Logical_Rest < Addr_Per_Block then
         Indirect_Block_Lookup
           (Indirect_Block_Phys  => FSBlock_Offset (State.Indirect_Block),
            Addr_In_Block        => Addr_In_Block_Range (Logical_Rest),
            Level                => Last_Level,
            Logical_Off          => Logical - Logical_Rest,
            Next_Physical        => Physical,
            Success              => Success);
         return;
      end if;

      Logical_Rest := Logical_Rest - Addr_Per_Block;
      if Logical_Rest < Addr_Per_Block ** 2 then
         Indirect_Block_Lookup
           (Indirect_Block_Phys  => FSBlock_Offset (State.Double_Indirect),
            Addr_In_Block        => Addr_In_Block_Range (Logical_Rest / Addr_Per_Block),
            Level                => Second_Last_Level,
            Logical_Off          => Logical - Logical_Rest,
            Next_Physical        => Physical,
            Success              => Success);
         if not Success then
            return;
         end if;

         Indirect_Block_Lookup
           (Indirect_Block_Phys  => Physical,
            Addr_In_Block        => Addr_In_Block_Range (Logical_Rest mod Addr_Per_Block),
            Level                => Last_Level,
            Logical_Off          => Logical - (Logical_Rest mod Addr_Per_Block),
            Next_Physical        => Physical,
            Success              => Success);
         return;
      end if;

      Logical_Rest := Logical_Rest - Addr_Per_Block ** 2;
      if Logical_Rest < Addr_Per_Block ** 3 then
         Indirect_Block_Lookup
           (Indirect_Block_Phys  => FSBlock_Offset (State.Triple_Indirect),
            Addr_In_Block        => Addr_In_Block_Range (Logical_Rest / Addr_Per_Block ** 2),
            Level                => First_Level,
            Logical_Off          => Logical - Logical_Rest,
            Next_Physical        => Physical,
            Success              => Success);
         if not Success then
            return;
         end if;

         Indirect_Block_Lookup
           (Indirect_Block_Phys  => Physical,
            Addr_In_Block        => Addr_In_Block_Range (Logical_Rest / Addr_Per_Block mod Addr_Per_Block),
            Level                => Second_Last_Level,
            Logical_Off          => Logical - (Logical_Rest mod Addr_Per_Block ** 2),
            Next_Physical        => Physical,
            Success              => Success);
         if not Success then
            return;
         end if;

         Indirect_Block_Lookup
           (Indirect_Block_Phys  => Physical,
            Addr_In_Block        => Addr_In_Block_Range (Logical_Rest mod Addr_Per_Block),
            Level                => Last_Level,
            Logical_Off          => Logical - (Logical_Rest mod Addr_Per_Block),
            Next_Physical        => Physical,
            Success              => Success);
         return;
      end if;

      -- Logical address was just too high.
      Success := False;
   end Ext2_Block_Map;

   procedure Open
     (State       : in out T;
      File_Len    :    out File_Length;
      File_Path   : in     String;
      Success     : out    Boolean)
   is
   begin
      File_Len := 0;
      Success := False;
   end Open;

   procedure Close (State : in out T) is
   begin
      State.S := Mounted;
   end Close;

   procedure Read
     (State    : in out T;
      File_Len : in     File_Length;
      File_Pos : in out File_Offset;
      Buf      :    out Buffer_Type;
      Len      :    out Natural)
   is
   begin
      Buf := (others => 0);
      Len := 0;
   end Read;

   --------------------------------------------------------------------------

   package C is new VFS (T => T, Initial => (S => Unmounted, others => <>));

   function C_Mount return int
   with
      Export,
      Convention => C,
      External_Name => "ext2fs_mount";
   function C_Mount return int
   with
      SPARK_Mode => Off
   is
   begin
      return C.C_Mount;
   end C_Mount;

   function C_Open (File_Path : Strings.chars_ptr) return int
   with
      Export,
      Convention => C,
      External_Name => "ext2fs_dir";
   function C_Open (File_Path : Strings.chars_ptr) return int
   with
      SPARK_Mode => Off
   is
   begin
      return C.C_Open (File_Path);
   end C_Open;

   function C_Read (Buf : System.Address; Len : int) return int
   with
      Export,
      Convention => C,
      External_Name => "ext2fs_read";
   function C_Read (Buf : System.Address; Len : int) return int
   with
      SPARK_Mode => Off
   is
   begin
      return C.C_Read (Buf, Len);
   end C_Read;

end FILO.FS.Ext2;