#!/usr/bin/env python3
"""
Scan ext4 filesystem for orphaned directory roots.
Reads inode table directly using geometry from backup superblock.
"""
import struct, sys
from collections import defaultdict

DEV = '/dev/dm-0'
BLOCK = 4096
BACKUP_SB_BLOCK = 32768

def read_at(f, offset, size):
    f.seek(offset)
    return f.read(size)

def parse_superblock(data):
    sb = {}
    sb['inodes_count']      = struct.unpack_from('<I', data,  0)[0]
    sb['blocks_count']      = struct.unpack_from('<I', data,  4)[0]
    sb['blocks_per_group']  = struct.unpack_from('<I', data, 32)[0]
    sb['inodes_per_group']  = struct.unpack_from('<I', data, 40)[0]
    sb['inode_size']        = struct.unpack_from('<H', data, 88)[0]
    sb['magic']             = struct.unpack_from('<H', data, 56)[0]
    sb['feature_incompat']  = struct.unpack_from('<I', data, 96)[0]
    sb['desc_size']         = struct.unpack_from('<H', data, 254)[0] or 32
    return sb

def parse_gdt_entry(data, offset, desc_size):
    """Parse group descriptor - handles both 32 and 64-bit descriptors"""
    inode_table_lo = struct.unpack_from('<I', data, offset + 8)[0]
    if desc_size >= 64:
        inode_table_hi = struct.unpack_from('<I', data, offset + 40)[0]
        return inode_table_lo | (inode_table_hi << 32)
    return inode_table_lo

def parse_extent_tree(data, inode_offset):
    base = inode_offset + 40
    magic, entries, max_entries, depth = struct.unpack_from('<HHHH', data, base)

    if magic != 0xF30A:
        return []

    extents = []
    if depth == 0:
        for i in range(min(entries, 4)):
            ext_off = base + 12 + i * 12
            if ext_off + 12 > len(data):
                break
            # Correct layout: l_block(4) + ee_len(2) + ee_start_hi(2) + ee_start_lo(4)
            l_block  = struct.unpack_from('<I', data, ext_off)[0]
            ee_len   = struct.unpack_from('<H', data, ext_off + 4)[0]
            start_hi = struct.unpack_from('<H', data, ext_off + 6)[0]
            start_lo = struct.unpack_from('<I', data, ext_off + 8)[0]
            phys = (start_hi << 32) | start_lo
            if phys > 0:
                extents.append((l_block, phys, ee_len & 0x7FFF))
    return extents

def read_dir_entries(f, inode_data, inode_offset):
    """Read directory entries using extent tree from inode data"""
    extents = parse_extent_tree(inode_data, inode_offset)
    entries = {}
    for _, phys_block, length in extents[:1]:  # first extent is enough for . and ..
        try:
            data = read_at(f, phys_block * BLOCK, BLOCK)
            offset = 0
            while offset < BLOCK - 8:
                ino, rec_len, name_len, ftype = struct.unpack_from(
                    '<IHBB', data, offset)
                if rec_len < 8 or offset + rec_len > BLOCK:
                    break
                if ino != 0 and name_len > 0:
                    name = data[offset+8:offset+8+name_len].decode(
                        'utf-8', errors='replace')
                    entries[name] = (ino, ftype)
                offset += rec_len
        except OSError:
            pass
    return entries

def parse_inode(data, offset):
    if len(data) - offset < 128:
        return None
    mode, uid, size_lo = struct.unpack_from('<HHI', data, offset)
    atime, ctime, mtime, dtime = struct.unpack_from('<IIII', data, offset + 8)
    links_count = struct.unpack_from('<H', data, offset + 26)[0]
    # block pointers start at offset 40, 60 bytes (12 direct + ind + dind + tind)
    block0 = struct.unpack_from('<I', data, offset + 40)[0]
    return {
        'mode': mode,
        'type': mode & 0xF000,
        'links': links_count,
        'ctime': ctime,
        'mtime': mtime,
        'block0': block0,  # first direct block pointer
    }

def main():
    with open(DEV, 'rb') as f:
        # Read backup superblock (no +1024 offset for backup blocks)
        sb_data = read_at(f, BACKUP_SB_BLOCK * BLOCK, 1024)
        sb = parse_superblock(sb_data)
        # After parsing superblock, check feature flags

        INCOMPAT_EXTENTS = 0x40
        uses_extents = sb['feature_incompat'] & INCOMPAT_EXTENTS
        print(f"Extent trees: {'yes' if uses_extents else 'no'}")
        
        assert sb['magic'] == 0xef53, f"Bad SB magic: {sb['magic']:#x}"
        print(f"Geometry: {sb['blocks_per_group']} blk/grp, "
              f"{sb['inodes_per_group']} ino/grp, "
              f"inode_size={sb['inode_size']}, "
              f"desc_size={sb['desc_size']}")

        num_groups = (sb['blocks_count'] + sb['blocks_per_group'] - 1) \
                     // sb['blocks_per_group']
        print(f"Total groups: {num_groups}, scanning from group 13+")

        # Read GDT from backup location (block after backup SB)
        gdt_data = read_at(f, (BACKUP_SB_BLOCK + 1) * BLOCK, 
                           num_groups * sb['desc_size'])

        # Map: inode_num -> (parent_inode, group, name)
        # We collect (dot_inode, dotdot_inode) for every dir we find
        dir_parents = {}   # inode -> parent_inode
        all_dirs    = set()

        for grp in range(13, num_groups):
            inode_table_block = parse_gdt_entry(
                gdt_data, grp * sb['desc_size'], sb['desc_size'])
            if inode_table_block == 0:
                continue

            inodes_per_block = BLOCK // sb['inode_size']
            num_inode_blocks = (sb['inodes_per_group'] * sb['inode_size'] 
                                + BLOCK - 1) // BLOCK

            for blk_off in range(num_inode_blocks):
                try:
                    idata = read_at(f, 
                        (inode_table_block + blk_off) * BLOCK, BLOCK)
                except OSError:
                    continue

                for slot in range(inodes_per_block):
                    ino_off = slot * sb['inode_size']
                    ino = parse_inode(idata, ino_off)
                    if ino is None:
                        continue
                    if ino['type'] != 0x4000:  # S_IFDIR
                        continue
                    if ino['links'] == 0:
                        continue

                    abs_inum = (grp * sb['inodes_per_group'] 
                                + blk_off * inodes_per_block 
                                + slot + 1)
                    all_dirs.add(abs_inum)
                    # Add this debug block right after all_dirs.add(abs_inum)
                    # Just for the first 5 dirs found, dump raw extent header
                    if len(all_dirs) <= 5:
                        base = ino_off + 40
                        raw = idata[base:base+24]
                        magic, entries_cnt, max_e, depth = struct.unpack_from('<HHHH', raw, 0)
                        print(f"\nDEBUG inode {abs_inum} grp={grp}:")
                        print(f"  raw bytes: {raw.hex()}")
                        print(f"  extent header: magic={magic:#06x} entries={entries_cnt} depth={depth}")
                        if len(raw) >= 24:
                            l_block, len_blks, start_hi, start_lo = struct.unpack_from('<IIHH', raw, 12)
                            phys = (start_hi << 32) | start_lo
                            print(f"  first extent: l_block={l_block} phys={phys} len={len_blks}")
                            # Try reading what's at that block
                            if phys > 0:
                                try:
                                    ddata = read_at(f, phys * BLOCK, 32)
                                    print(f"  block {phys} first 32 bytes: {ddata.hex()}")
                                    # Check if it looks like a dir entry
                                    ino2, rec2, nlen2, ft2 = struct.unpack_from('<IHBB', ddata, 0)
                                    print(f"  as dir entry: inode={ino2} rec_len={rec2} name_len={nlen2}")
                                except OSError as e:
                                    print(f"  read error: {e}")

                    entries = read_dir_entries(f, idata, ino_off)
                    
                    dot    = entries.get('.',  (None,))[0]
                    dotdot = entries.get('..', (None,))[0]

                    if dot == abs_inum and dotdot is not None:
                        dir_parents[abs_inum] = dotdot

            if grp % 100 == 0:
                print(f"  scanned group {grp}/{num_groups}, "
                      f"dirs so far: {len(all_dirs)}", 
                      end='\r', flush=True)

        print(f"\nTotal dirs found: {len(all_dirs)}")
        print(f"Dirs with readable . and ..: {len(dir_parents)}")

        FIRST_GOOD_INODE = 13 * 8192  # first inode in group 13

        orphan_roots = []
        for inum, parent in dir_parents.items():
            if parent == inum:
                orphan_roots.append((inum, parent, 'self-referential'))
            elif parent < FIRST_GOOD_INODE:
                # parent is in zeroed region - this is a detached root
                orphan_roots.append((inum, parent, 'parent-in-zeroed-region'))
            elif parent not in all_dirs:
                orphan_roots.append((inum, parent, 'parent-missing'))

        print(f"\nOrphaned roots: {len(orphan_roots)}")
        print(f"{'inode':>12}  {'parent':>12}  reason")
        print('-' * 45)
        for inum, parent, reason in sorted(orphan_roots):
            print(f"{inum:>12}  {parent:>12}  {reason}")
        # Add this after the orphan_roots list is built

        # Build set of all orphaned inodes
        orphan_inums = {inum for inum, parent, reason in orphan_roots}

        # True roots: orphans whose parent is not itself an orphan
        true_roots = [(inum, parent, reason) 
                      for inum, parent, reason in orphan_roots
                      if parent not in orphan_inums]

        print(f"\nTrue detached tree roots: {len(true_roots)}")
        print(f"{'inode':>12}  {'parent':>12}  reason")
        print('-' * 55)
        for inum, parent, reason in sorted(true_roots):
            # Try to get first few dir entries to identify the tree
            with open(DEV, 'rb') as f:
                grp = (inum - 1) // sb['inodes_per_group']
                local_idx = (inum - 1) % sb['inodes_per_group']
                inode_table_block = parse_gdt_entry(
                    gdt_data, grp * sb['desc_size'], sb['desc_size'])
                blk_off = (local_idx * sb['inode_size']) // BLOCK
                slot = (local_idx * sb['inode_size']) % BLOCK
                idata = read_at(f, (inode_table_block + blk_off) * BLOCK, BLOCK)
                entries = read_dir_entries(f, idata, slot)
                # Show entries excluding . and ..
                names = [k for k in entries if k not in ('.', '..')][:5]
            print(f"{inum:>12}  {parent:>12}  {names}") 

if __name__ == '__main__':
    main()
