rumpk/core/fs/tar.nim

# MARKUS MAIWALD (ARCHITECT) | VOXIS FORGE (AI)
# Rumpk L1: Sovereign VFS (Indexing TarFS)

{.push stackTrace: off, lineTrace: off.}

import std/tables

# Kernel Imports (Avoid circular dependency)
proc kprint(s: cstring) {.importc, cdecl.}
proc kprintln(s: cstring) {.importc, cdecl.}
proc kprint_hex(n: uint64) {.importc, cdecl.} # Assuming this exists or I need to implement it equivalent

# --- TAR HEADER DEF (USTAR) ---
type
  TarHeader* {.packed.} = object
    name*: array[100, char]
    mode*: array[8, char]
    uid*: array[8, char]
    gid*: array[8, char]
    size*: array[12, char]
    mtime*: array[12, char]
    chksum*: array[8, char]
    typeflag*: char
    linkname*: array[100, char]
    magic*: array[6, char]
    version*: array[2, char]
    uname*: array[32, char]
    gname*: array[32, char]
    devmajor*: array[8, char]
    devminor*: array[8, char]
    prefix*: array[155, char]
    # Padding to 512 handled by jump logic

  FileEntry = object
    offset*: uint64
    size*: uint64

  FileHandle = object
    path*: string
    offset*: uint64

  VFSInitRD* = object
    start_addr*: uint64
    end_addr*: uint64
    index*: Table[string, FileEntry]
    fds*: Table[int, FileHandle]
    next_fd*: int

var vfs*: VFSInitRD

# --- HELPERS ---

proc parse_octal(a: openArray[char]): uint64 =
  var res: uint64 = 0
  var started = false
  for c in a:
    if c >= '0' and c <= '7':
      res = (res shl 3) or (uint64(c) - uint64('0'))
      started = true
    elif started:
      break
  return res

proc align_512(n: uint64): uint64 =
  if (n and 511) != 0:
    return (n + 512) and not 511'u64
  return n

proc cstring_to_nim(ptr_char: ptr char, max_len: int): string =
  var res = newStringOfCap(max_len)
  var p = ptr_char
  var i = 0
  while i < max_len and p[] != '\0':
    res.add(p[])
    p = cast[ptr char](cast[uint64](p) + 1)
    i += 1
  return res

# --- API ---

proc vfs_init*(s: pointer, e: pointer) =
  vfs.start_addr = cast[uint64](s)
  vfs.end_addr = cast[uint64](e)
  vfs.index = initTable[string, FileEntry]()
  vfs.fds = initTable[int, FileHandle]()
  vfs.next_fd = 3 # 0,1,2 reserved

  kprint("[VFS] Mounting TarFS InitRD... Start=")
  kprint_hex(vfs.start_addr)
  kprint(" End=")
  kprint_hex(vfs.end_addr)
  kprint(" Size=")
  kprint_hex(vfs.end_addr - vfs.start_addr)
  kprintln("")

  var ptr_curr = vfs.start_addr

  while ptr_curr < vfs.end_addr:
    let header = cast[ptr TarHeader](ptr_curr)

    # Check bounds safety before reading header
    if ptr_curr + 512 > vfs.end_addr: break

    # Check End of Archive (Empty Block)
    if header.name[0] == '\0': break

    let fname = cstring_to_nim(addr header.name[0], 100)
    let size = parse_octal(header.size)
    discard parse_octal(header.mode)


    var clean_name = fname
    if clean_name.len >= 2 and clean_name[0] == '.' and clean_name[1] == '/':
      clean_name = clean_name[2..^1]

    # Index Files (Type '0' or '\0')
    if header.typeflag == '0' or header.typeflag == '\0':
      if clean_name.len > 0:
        let data_offset = ptr_curr + 512
        vfs.index[clean_name] = FileEntry(offset: data_offset, size: size)

    # Jump to next header
    ptr_curr += 512 + align_512(size)

proc vfs_open*(path: string): int =
  if vfs.index.hasKey(path):
    let fd = vfs.next_fd
    vfs.fds[fd] = FileHandle(path: path, offset: 0)
    vfs.next_fd += 1
    return fd
  return -1

proc vfs_get_entry*(path: string): (pointer, uint64) =
  if vfs.index.hasKey(path):
    let entry = vfs.index[path]
    return (cast[pointer](entry.offset), entry.size)
  return (nil, 0)

# --- C EXPORTS (THE BRIDGE) ---

proc ion_vfs_open*(path: cstring): int32 {.exportc, cdecl.} =
  return int32(vfs_open($path))

proc ion_vfs_read*(fd: int32, buf: pointer, count: uint64): int64 {.exportc, cdecl.} =
  let fd_int = int(fd)
  if not vfs.fds.hasKey(fd_int): return -1

  var fh = vfs.fds[fd_int] # Get a mutable copy of the FileHandle
  let (base_ptr, total_size) = vfs_get_entry(fh.path)

  if base_ptr == nil: return 0
  if fh.offset >= total_size: return 0 # EOF

  # Calculate remaining bytes
  let remaining = total_size - fh.offset
  let to_read = min(uint64(remaining), count)

  if to_read > 0:
    let data_ptr = cast[pointer](cast[uint64](base_ptr) + fh.offset)
    copyMem(buf, data_ptr, to_read)

    # Update cursor
    fh.offset += to_read
    vfs.fds[fd_int] = fh # Write back to table

    return int64(to_read)

  return 0

proc vfs_list_files*(): string =
  var res = ""
  for name, entry in vfs.index:
    res.add(name)
    res.add("\n")
  return res

proc ion_vfs_list*(buf: pointer, max_len: uint64): int64 {.exportc, cdecl.} =
  let list = vfs_list_files()
  let len = min(list.len, int(max_len))
  if len > 0:
    copyMem(buf, unsafeAddr list[0], len)
  return int64(len)

proc vfs_read_file*(path: string): string =
  if vfs.index.hasKey(path):
    let entry = vfs.index[path]
    let ptr_data = cast[ptr UncheckedArray[char]](entry.offset)
    var s = newString(entry.size)
    if entry.size > 0:
      copyMem(addr s[0], ptr_data, entry.size)
    return s

  return ""


{.pop.}