use std::{
    fs::{create_dir_all, File, FileTimes, OpenOptions},
    io::{self, BufRead, BufReader, Read, Seek, SeekFrom, Write},
    path::Path,
    time::{Duration, SystemTime},
};

use anyhow::{anyhow, Result};
use indicatif::{ProgressBar, ProgressStyle};
use ntfs::{
    structured_values::{NtfsFileNamespace, NtfsStandardInformation},
    Ntfs, NtfsAttributeType, NtfsTime,
};

// ---------------------------------------------------------------------------
// Constants
// ---------------------------------------------------------------------------

const SECTOR_SIZE: u64 = 512;
const BUF_SIZE: usize = 256 * 1024;

// VHD format
const VHD_COOKIE: &[u8; 8] = b"conectix";
const VHD_TYPE_FIXED: u32 = 2;
const VHD_TYPE_DYNAMIC: u32 = 3;
const VHD_TYPE_DIFFERENCING: u32 = 4;
const VHD_FOOTER_DISK_TYPE_OFFSET: usize = 0x3C;
const VHD_FOOTER_DATA_OFFSET: usize = 0x10;
/// VHD footer Unique Id (GUID), 16 bytes at offset 68 (0x44) — identifies this VHD.
const VHD_FOOTER_UNIQUE_ID_OFFSET: usize = 0x44;

// Dynamic/differencing VHD header
const DYNAMIC_HEADER_COOKIE: &[u8; 8] = b"cxsparse";
const DYNAMIC_HEADER_SIZE: usize = 1024;
const DYNAMIC_BAT_OFFSET_FIELD: usize = 0x10;
const DYNAMIC_MAX_ENTRIES_FIELD: usize = 0x18;
const DYNAMIC_BLOCK_SIZE_FIELD: usize = 0x20;
/// Dynamic header Parent Unique ID (GUID), 16 bytes at offset 40 (0x28) — only
/// meaningful for differencing VHDs; points at the parent VHD's footer Unique Id.
const DYNAMIC_PARENT_UNIQUE_ID_OFFSET: usize = 0x28;
const BAT_UNUSED: u32 = 0xFFFFFFFF;

pub type VhdGuid = [u8; 16];

/// Chain-linking info read from a VHD. `parent_id` is `Some` only for differencing
/// disks (type 4), and points at the parent VHD's `own_id`.
#[derive(Debug, Clone)]
pub struct VhdGuidInfo {
    pub own_id: VhdGuid,
    pub parent_id: Option<VhdGuid>,
    /// Kept for diagnostics / future validation; not every caller inspects it.
    #[allow(dead_code)]
    pub disk_type: u32,
}

/// Read a VHD's Unique Id and (for differencing VHDs) its Parent Unique ID.
/// Cheap — only reads the 512-byte footer plus, if differencing, the 1024-byte
/// dynamic header. Used to build chains by matching child.parent_id -> parent.own_id.
pub fn read_vhd_guid_info(path: &Path) -> Result<VhdGuidInfo, VhdError> {
    let mut f = File::open(path)?;
    let size = f.seek(SeekFrom::End(0))?;
    if size < SECTOR_SIZE {
        return Err(VhdError::InvalidCookie);
    }
    f.seek(SeekFrom::Start(size - SECTOR_SIZE))?;
    let mut footer = [0u8; SECTOR_SIZE as usize];
    f.read_exact(&mut footer)?;
    if &footer[..8] != VHD_COOKIE {
        return Err(VhdError::InvalidCookie);
    }
    let own_id: VhdGuid = footer[VHD_FOOTER_UNIQUE_ID_OFFSET..VHD_FOOTER_UNIQUE_ID_OFFSET + 16]
        .try_into()
        .unwrap();
    let disk_type = read_be_u32(&footer, VHD_FOOTER_DISK_TYPE_OFFSET);

    let parent_id = if disk_type == VHD_TYPE_DIFFERENCING {
        let header_offset = read_be_u64(&footer, VHD_FOOTER_DATA_OFFSET);
        f.seek(SeekFrom::Start(header_offset))?;
        let mut hdr = [0u8; DYNAMIC_HEADER_SIZE];
        f.read_exact(&mut hdr)?;
        if &hdr[..8] != DYNAMIC_HEADER_COOKIE {
            return Err(VhdError::InvalidDynamicHeader);
        }
        let guid: VhdGuid = hdr
            [DYNAMIC_PARENT_UNIQUE_ID_OFFSET..DYNAMIC_PARENT_UNIQUE_ID_OFFSET + 16]
            .try_into()
            .unwrap();
        Some(guid)
    } else {
        None
    };

    Ok(VhdGuidInfo { own_id, parent_id, disk_type })
}

// MBR
const MBR_SIGNATURE: [u8; 2] = [0x55, 0xAA];
const MBR_PARTITION_TABLE_OFFSET: usize = 0x1BE;
const MBR_PARTITION_ENTRY_SIZE: usize = 16;
const MBR_MAX_PARTITIONS: usize = 4;
const NTFS_PARTITION_TYPE: u8 = 0x07;

// NTFS boot sector magic
const NTFS_MAGIC: [u8; 4] = [0xEB, 0x52, 0x90, 0x4E];
/// Common virtual offsets where NTFS boot sector might start.
const NTFS_PROBE_OFFSETS: [u64; 4] = [0, 32_256, 1_048_576, 512];

// Progress bar
const PROGRESS_STYLE: &str =
    "{prefix} [{bar:20!.bright.yellow/dim.white}] {bytes:>8} [{elapsed}<{eta}, {bytes_per_sec}]";

// Windows epoch -> Unix epoch offset (100ns intervals)
const WINDOWS_EPOCH_OFFSET: u64 = 116_444_736_000_000_000;

// ---------------------------------------------------------------------------
// VHD error type
// ---------------------------------------------------------------------------

#[derive(Debug, thiserror::Error)]
pub enum VhdError {
    #[error(transparent)]
    Io(#[from] io::Error),
    #[error("Not a valid VHD file")]
    InvalidCookie,
    #[error("Unsupported VHD type {0}")]
    UnsupportedType(u32),
    #[error("Invalid dynamic VHD header")]
    InvalidDynamicHeader,
    #[error("No NTFS partition found in VHD")]
    NoNtfsPartition,
}

// ---------------------------------------------------------------------------
// VHD layout: how to map virtual offsets to file offsets
// ---------------------------------------------------------------------------

enum VhdLayout {
    /// Data is contiguous from offset 0 to (file_size - 512).
    Fixed,
    /// Data is in blocks addressed via a Block Allocation Table.
    /// Used for both dynamic (type 3) and differencing (type 4) VHDs.
    Sparse { bat: Vec<u32>, block_size: u64 },
}

impl VhdLayout {
    /// Parse the dynamic/differencing header and BAT.
    fn parse_sparse<R: Read + Seek>(inner: &mut R, footer: &[u8]) -> Result<(Self, u64), VhdError> {
        let header_offset = read_be_u64(footer, VHD_FOOTER_DATA_OFFSET);

        inner.seek(SeekFrom::Start(header_offset))?;
        let mut hdr = [0u8; DYNAMIC_HEADER_SIZE];
        inner.read_exact(&mut hdr)?;
        if &hdr[..8] != DYNAMIC_HEADER_COOKIE {
            return Err(VhdError::InvalidDynamicHeader);
        }

        let bat_offset = read_be_u64(&hdr, DYNAMIC_BAT_OFFSET_FIELD);
        let max_entries = read_be_u32(&hdr, DYNAMIC_MAX_ENTRIES_FIELD) as usize;
        let block_size = read_be_u32(&hdr, DYNAMIC_BLOCK_SIZE_FIELD) as u64;

        inner.seek(SeekFrom::Start(bat_offset))?;
        let mut raw = vec![0u8; max_entries * 4];
        inner.read_exact(&mut raw)?;
        let bat: Vec<u32> = (0..max_entries).map(|i| read_be_u32(&raw, i * 4)).collect();

        Ok((VhdLayout::Sparse { bat, block_size }, max_entries as u64 * block_size))
    }

    /// Read bytes from a virtual offset according to this layout.
    fn read_at<R: Read + Seek>(
        &self,
        inner: &mut R,
        virt_off: u64,
        virtual_size: u64,
        buf: &mut [u8],
    ) -> io::Result<usize> {
        if virt_off >= virtual_size {
            return Ok(0);
        }
        let cap = std::cmp::min(buf.len() as u64, virtual_size - virt_off) as usize;

        match self {
            VhdLayout::Fixed => {
                inner.seek(SeekFrom::Start(virt_off))?;
                inner.read(&mut buf[..cap])
            }
            VhdLayout::Sparse { bat, block_size } => {
                let bi = (virt_off / block_size) as usize;
                let bo = virt_off % block_size;
                let n = std::cmp::min(cap, (block_size - bo) as usize);

                if bi >= bat.len() || bat[bi] == BAT_UNUSED {
                    buf[..n].fill(0);
                    Ok(n)
                } else {
                    // Each block: bitmap sector + data. Skip bitmap.
                    let file_off = bat[bi] as u64 * SECTOR_SIZE + SECTOR_SIZE + bo;
                    inner.seek(SeekFrom::Start(file_off))?;
                    inner.read(&mut buf[..n])
                }
            }
        }
    }

    /// Read 4 bytes from a virtual offset (for magic-byte probing).
    fn read_magic<R: Read + Seek>(
        &self,
        inner: &mut R,
        offset: u64,
    ) -> io::Result<[u8; 4]> {
        let mut buf = [0u8; 4];
        match self {
            VhdLayout::Fixed => {
                inner.seek(SeekFrom::Start(offset))?;
                inner.read_exact(&mut buf)?;
            }
            VhdLayout::Sparse { bat, block_size } => {
                let bi = (offset / block_size) as usize;
                if bi < bat.len() && bat[bi] != BAT_UNUSED {
                    let file_off = bat[bi] as u64 * SECTOR_SIZE + SECTOR_SIZE + offset % block_size;
                    inner.seek(SeekFrom::Start(file_off))?;
                    inner.read_exact(&mut buf)?;
                }
            }
        }
        Ok(buf)
    }
}

// ---------------------------------------------------------------------------
// VHD reader (single VHD)
// ---------------------------------------------------------------------------

/// Transparently presents the NTFS partition within a fixed or dynamic VHD.
pub struct VhdReader<R> {
    inner: R,
    layout: VhdLayout,
    ntfs_offset: u64,
    virtual_size: u64,
    pos: u64,
}

impl<R: Read + Seek> VhdReader<R> {
    pub fn new(mut inner: R) -> Result<Self, VhdError> {
        let file_size = inner.seek(SeekFrom::End(0))?;
        if file_size < SECTOR_SIZE {
            return Err(VhdError::InvalidCookie);
        }

        inner.seek(SeekFrom::Start(file_size - SECTOR_SIZE))?;
        let mut footer = [0u8; SECTOR_SIZE as usize];
        inner.read_exact(&mut footer)?;
        if &footer[..8] != VHD_COOKIE {
            return Err(VhdError::InvalidCookie);
        }

        let disk_type = read_be_u32(&footer, VHD_FOOTER_DISK_TYPE_OFFSET);
        let (layout, virtual_size) = match disk_type {
            VHD_TYPE_FIXED => (VhdLayout::Fixed, file_size - SECTOR_SIZE),
            VHD_TYPE_DYNAMIC | VHD_TYPE_DIFFERENCING => {
                VhdLayout::parse_sparse(&mut inner, &footer)?
            }
            t => return Err(VhdError::UnsupportedType(t)),
        };

        let ntfs_offset = find_ntfs_offset(&mut inner, &layout, virtual_size)?;
        Ok(Self { inner, layout, ntfs_offset, virtual_size, pos: 0 })
    }

    fn ntfs_size(&self) -> u64 {
        self.virtual_size - self.ntfs_offset
    }
}

impl<R: Read + Seek> Read for VhdReader<R> {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        let remaining = self.ntfs_size().saturating_sub(self.pos);
        if remaining == 0 {
            return Ok(0);
        }
        let cap = std::cmp::min(buf.len() as u64, remaining) as usize;
        let n = self.layout.read_at(
            &mut self.inner, self.ntfs_offset + self.pos, self.virtual_size, &mut buf[..cap],
        )?;
        self.pos += n as u64;
        Ok(n)
    }
}

impl<R: Read + Seek> Seek for VhdReader<R> {
    fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
        let target = match pos {
            SeekFrom::Start(o) => o as i64,
            SeekFrom::Current(o) => self.pos as i64 + o,
            SeekFrom::End(o) => self.ntfs_size() as i64 + o,
        };
        if target < 0 {
            return Err(io::Error::new(io::ErrorKind::InvalidInput, "seek before start"));
        }
        self.pos = target as u64;
        Ok(self.pos)
    }
}

// ---------------------------------------------------------------------------
// Chained VHD reader (base + N deltas overlaid, no on-disk merge needed)
// ---------------------------------------------------------------------------

/// One layer of a VHD chain: a file handle plus its parsed layout.
struct VhdLayer<R> {
    inner: R,
    layout: VhdLayout,
}

/// Reads from a chain of VHDs where `layers[0]` is the base (dynamic/fixed)
/// and `layers[1..]` are differencing VHDs in parent→child order.
///
/// For each read, walks layers from top delta down to base. At each layer,
/// if the sector is present-and-modified (BAT allocated + bitmap bit set),
/// that layer's bytes win; otherwise the read falls through to the layer
/// below. The base layer's own `read_at` handles zero-fill for unallocated
/// dynamic blocks.
pub struct ChainedVhdReader<R> {
    layers: Vec<VhdLayer<R>>,
    ntfs_offset: u64,
    virtual_size: u64,
    pos: u64,
}

impl<R: Read + Seek> ChainedVhdReader<R> {
    /// Build a chain reader. `readers` must be ordered base-first, top-most delta last.
    pub fn new(readers: Vec<R>) -> Result<Self, VhdError> {
        if readers.is_empty() {
            return Err(VhdError::InvalidCookie);
        }

        let mut layers: Vec<VhdLayer<R>> = Vec::with_capacity(readers.len());
        let mut virtual_size = 0u64;

        for (idx, mut r) in readers.into_iter().enumerate() {
            let file_size = r.seek(SeekFrom::End(0))?;
            if file_size < SECTOR_SIZE {
                return Err(VhdError::InvalidCookie);
            }
            r.seek(SeekFrom::Start(file_size - SECTOR_SIZE))?;
            let mut footer = [0u8; SECTOR_SIZE as usize];
            r.read_exact(&mut footer)?;
            if &footer[..8] != VHD_COOKIE {
                return Err(VhdError::InvalidCookie);
            }
            let disk_type = read_be_u32(&footer, VHD_FOOTER_DISK_TYPE_OFFSET);
            let (layout, vsize) = match disk_type {
                VHD_TYPE_FIXED => (VhdLayout::Fixed, file_size - SECTOR_SIZE),
                VHD_TYPE_DYNAMIC | VHD_TYPE_DIFFERENCING => {
                    VhdLayout::parse_sparse(&mut r, &footer)?
                }
                t => return Err(VhdError::UnsupportedType(t)),
            };
            if idx == 0 {
                virtual_size = vsize;
            }
            layers.push(VhdLayer { inner: r, layout });
        }

        let ntfs_offset = find_ntfs_offset_chain(&mut layers, virtual_size)?;

        Ok(Self { layers, ntfs_offset, virtual_size, pos: 0 })
    }

    fn ntfs_size(&self) -> u64 {
        self.virtual_size - self.ntfs_offset
    }
}

/// If `layer` has the sector for `virt_off` present AND marked modified in
/// its bitmap, read from it and return `Some(bytes_read)`. Otherwise `None`
/// signals "fall through to the layer below".
///
/// Reads are capped at the current sector boundary. The VHD bitmap is
/// per-sector: a single block can have a mixed 1/0 pattern, so a larger read
/// might cross a sector that belongs to a different layer. The Read
/// implementation loops until `buf` is filled, amortising the extra calls.
fn try_read_from_layer<R: Read + Seek>(
    layer: &mut VhdLayer<R>,
    virt_off: u64,
    buf: &mut [u8],
) -> io::Result<Option<usize>> {
    match &layer.layout {
        VhdLayout::Fixed => Ok(None), // Fixed deltas make no sense; fall through.
        VhdLayout::Sparse { bat, block_size } => {
            let bi = (virt_off / block_size) as usize;
            let bo = virt_off % block_size;
            if bi >= bat.len() || bat[bi] == BAT_UNUSED {
                return Ok(None);
            }

            // Cap at the current sector to honour per-sector bitmap semantics.
            let sector_remaining = (SECTOR_SIZE - (virt_off % SECTOR_SIZE)) as usize;
            let n = std::cmp::min(buf.len(), sector_remaining);
            let block_file_offset = bat[bi] as u64 * SECTOR_SIZE;

            // Read the block's bitmap sector.
            layer.inner.seek(SeekFrom::Start(block_file_offset))?;
            let mut bitmap = [0u8; SECTOR_SIZE as usize];
            layer.inner.read_exact(&mut bitmap)?;

            let sector_in_block = (bo / SECTOR_SIZE) as usize;
            let bitmap_byte = bitmap[sector_in_block / 8];
            let bitmap_bit = 7 - (sector_in_block % 8); // MSB first
            if (bitmap_byte >> bitmap_bit) & 1 == 0 {
                return Ok(None);
            }

            let file_off = block_file_offset + SECTOR_SIZE + bo;
            layer.inner.seek(SeekFrom::Start(file_off))?;
            let got = layer.inner.read(&mut buf[..n])?;
            Ok(Some(got))
        }
    }
}

/// Walk layers top-to-bottom; first layer that owns the sector wins.
/// The base layer (index 0) always answers (possibly with zeros for
/// unallocated dynamic blocks).
fn read_chain<R: Read + Seek>(
    layers: &mut [VhdLayer<R>],
    vsize: u64,
    virt_off: u64,
    buf: &mut [u8],
) -> io::Result<usize> {
    if virt_off >= vsize {
        return Ok(0);
    }
    let cap = std::cmp::min(buf.len() as u64, vsize - virt_off) as usize;

    // Try deltas from top (last) down to just above base (index 1).
    for i in (1..layers.len()).rev() {
        if let Some(n) = try_read_from_layer(&mut layers[i], virt_off, &mut buf[..cap])? {
            return Ok(n);
        }
    }
    // Fall through to base.
    let base = &mut layers[0];
    base.layout.read_at(&mut base.inner, virt_off, vsize, &mut buf[..cap])
}

impl<R: Read + Seek> Read for ChainedVhdReader<R> {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        let remaining = self.ntfs_size().saturating_sub(self.pos);
        if remaining == 0 {
            return Ok(0);
        }
        let cap = std::cmp::min(buf.len() as u64, remaining) as usize;
        let virt_off = self.ntfs_offset + self.pos;
        let n = read_chain(&mut self.layers, self.virtual_size, virt_off, &mut buf[..cap])?;
        self.pos += n as u64;
        Ok(n)
    }
}

impl<R: Read + Seek> Seek for ChainedVhdReader<R> {
    fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
        let target = match pos {
            SeekFrom::Start(o) => o as i64,
            SeekFrom::Current(o) => self.pos as i64 + o,
            SeekFrom::End(o) => self.ntfs_size() as i64 + o,
        };
        if target < 0 {
            return Err(io::Error::new(io::ErrorKind::InvalidInput, "seek before start"));
        }
        self.pos = target as u64;
        Ok(self.pos)
    }
}

// ---------------------------------------------------------------------------
// NTFS partition detection (shared between single and merged readers)
// ---------------------------------------------------------------------------

/// Find NTFS offset in a single VHD.
fn find_ntfs_offset<R: Read + Seek>(
    inner: &mut R,
    layout: &VhdLayout,
    vsize: u64,
) -> Result<u64, VhdError> {
    // Try MBR
    if vsize >= SECTOR_SIZE {
        let mut mbr = [0u8; SECTOR_SIZE as usize];
        let _ = layout.read_at(inner, 0, vsize, &mut mbr);

        if mbr[510..512] == MBR_SIGNATURE {
            for i in 0..MBR_MAX_PARTITIONS {
                let eo = MBR_PARTITION_TABLE_OFFSET + i * MBR_PARTITION_ENTRY_SIZE;
                if mbr[eo + 4] == NTFS_PARTITION_TYPE {
                    let lba = u32::from_le_bytes(mbr[eo + 8..eo + 12].try_into().unwrap());
                    let offset = lba as u64 * SECTOR_SIZE;
                    if offset + 4 <= vsize && layout.read_magic(inner, offset)? == NTFS_MAGIC {
                        return Ok(offset);
                    }
                }
            }
        }
    }

    // Probe common offsets
    for offset in NTFS_PROBE_OFFSETS {
        if offset + 4 <= vsize && layout.read_magic(inner, offset)? == NTFS_MAGIC {
            return Ok(offset);
        }
    }

    Err(VhdError::NoNtfsPartition)
}

/// Find NTFS offset in a chained view (base + N deltas).
fn find_ntfs_offset_chain<R: Read + Seek>(
    layers: &mut [VhdLayer<R>],
    vsize: u64,
) -> Result<u64, VhdError> {
    // If the chain has only a base, defer to the single-VHD finder — it's simpler
    // and avoids the bitmap machinery for a pure dynamic/fixed disk.
    if layers.len() == 1 {
        let base = &mut layers[0];
        return find_ntfs_offset(&mut base.inner, &base.layout, vsize);
    }

    let read_magic = |layers: &mut [VhdLayer<R>], offset: u64| -> io::Result<[u8; 4]> {
        let mut buf = [0u8; 4];
        read_chain(layers, vsize, offset, &mut buf)?;
        Ok(buf)
    };

    // Try MBR from merged view.
    if vsize >= SECTOR_SIZE {
        let mut mbr = [0u8; SECTOR_SIZE as usize];
        read_chain(layers, vsize, 0, &mut mbr)?;

        if mbr[510..512] == MBR_SIGNATURE {
            for i in 0..MBR_MAX_PARTITIONS {
                let eo = MBR_PARTITION_TABLE_OFFSET + i * MBR_PARTITION_ENTRY_SIZE;
                if mbr[eo + 4] == NTFS_PARTITION_TYPE {
                    let lba = u32::from_le_bytes(mbr[eo + 8..eo + 12].try_into().unwrap());
                    let offset = lba as u64 * SECTOR_SIZE;
                    if offset + 4 <= vsize && read_magic(layers, offset)? == NTFS_MAGIC {
                        return Ok(offset);
                    }
                }
            }
        }
    }

    for offset in NTFS_PROBE_OFFSETS {
        if offset + 4 <= vsize && read_magic(layers, offset)? == NTFS_MAGIC {
            return Ok(offset);
        }
    }

    Err(VhdError::NoNtfsPartition)
}

// ---------------------------------------------------------------------------
// NTFS extraction (shared logic)
// ---------------------------------------------------------------------------

fn is_ntfs_system_entry(name: &str) -> bool {
    name.starts_with('$') || name == "." || name == ".." || name == "System Volume Information"
}

/// Whether a directory-index entry should be skipped when extracting.
///
/// Besides NTFS system metadata, this skips DOS (8.3) short-name aliases: a file
/// that has a separate short name appears in the index *twice* — once with its
/// Win32 long name and once with the `Dos` short name. Without this, every such
/// entry is extracted a second time under its mangled `NAME~1.EXT` name (and
/// short-named directories get their whole subtree duplicated).
fn skip_index_entry(namespace: NtfsFileNamespace, name: &str) -> bool {
    namespace == NtfsFileNamespace::Dos || is_ntfs_system_entry(name)
}

fn ntfs_time_to_system_time(t: NtfsTime) -> SystemTime {
    let nanos = (t.nt_timestamp() - WINDOWS_EPOCH_OFFSET) * 100;
    SystemTime::UNIX_EPOCH + Duration::from_nanos(nanos)
}

fn set_ntfs_timestamps<T: Read + Seek>(fs: &mut T, file: &ntfs::NtfsFile, path: &Path) {
    let mut attrs = file.attributes();
    while let Some(Ok(attr)) = attrs.next(fs) {
        if let Ok(attr) = attr.to_attribute() {
            if let Ok(NtfsAttributeType::StandardInformation) = attr.ty() {
                if let Ok(info) = attr.resident_structured_value::<NtfsStandardInformation>() {
                    let _ = OpenOptions::new().write(true).open(path).and_then(|h| {
                        h.set_times(
                            FileTimes::new()
                                .set_accessed(ntfs_time_to_system_time(info.access_time()))
                                .set_modified(ntfs_time_to_system_time(info.modification_time())),
                        )
                    });
                }
                break;
            }
        }
    }
}

fn extract_ntfs_dir<T: Read + Seek>(
    ntfs: &Ntfs,
    fs: &mut T,
    dir: &ntfs::NtfsFile,
    out: &Path,
    pb: &ProgressBar,
) -> Result<()> {
    let index = dir.directory_index(fs)?;
    let mut iter = index.entries();

    while let Some(entry) = iter.next(fs) {
        let entry = entry?;
        let key = entry.key().ok_or_else(|| anyhow!("missing key"))??;
        let name = key.name().to_string_lossy();
        if skip_index_entry(key.namespace(), &name) {
            continue;
        }

        let file = entry.to_file(ntfs, fs)?;
        let dest = out.join(&*name);

        if key.is_directory() {
            create_dir_all(&dest)?;
            extract_ntfs_dir(ntfs, fs, &file, &dest, pb)?;
            set_ntfs_timestamps(fs, &file, &dest);
        } else if let Some(data) = file.data(fs, "") {
            let data_item = data?;
            let attr = data_item.to_attribute()?;
            let mut reader = BufReader::with_capacity(BUF_SIZE, attr.value(fs)?.attach(fs));
            let mut out_file = File::create(&dest)?;

            loop {
                let buf = reader.fill_buf()?;
                if buf.is_empty() {
                    break;
                }
                out_file.write_all(buf)?;
                let n = buf.len();
                reader.consume(n);
                pb.inc(n as u64);
            }
            out_file.flush()?;
            drop(reader);
            set_ntfs_timestamps(fs, &file, &dest);
        }
    }
    Ok(())
}

fn calculate_ntfs_size<T: Read + Seek>(
    ntfs: &Ntfs,
    fs: &mut T,
    dir: &ntfs::NtfsFile,
) -> Result<u64> {
    let mut total = 0u64;
    let index = dir.directory_index(fs)?;
    let mut iter = index.entries();

    while let Some(entry) = iter.next(fs) {
        let entry = entry?;
        let key = entry.key().ok_or_else(|| anyhow!("missing key"))??;
        if skip_index_entry(key.namespace(), key.name().to_string_lossy().as_ref()) {
            continue;
        }
        let file = entry.to_file(ntfs, fs)?;
        if key.is_directory() {
            total += calculate_ntfs_size(ntfs, fs, &file)?;
        } else if let Some(data) = file.data(fs, "") {
            total += data?.to_attribute()?.value_length();
        }
    }
    Ok(total)
}

/// Shared extraction logic: given an NTFS-bearing Read+Seek, extract to output_dir.
fn extract_ntfs_to_dir<T: Read + Seek>(fs: &mut T, output_dir: &Path, prefix: &str) -> Result<()> {
    let mut ntfs = Ntfs::new(fs)?;
    ntfs.read_upcase_table(fs)?;

    let root = ntfs.root_directory(fs)?;
    let total = calculate_ntfs_size(&ntfs, fs, &root)?;

    let pb = ProgressBar::new(total)
        .with_style(ProgressStyle::default_bar().template(PROGRESS_STYLE)?);
    pb.set_prefix(prefix.to_string());

    create_dir_all(output_dir)?;
    let root = ntfs.root_directory(fs)?;
    extract_ntfs_dir(&ntfs, fs, &root, output_dir, &pb)?;
    pb.finish();

    Ok(())
}

// ---------------------------------------------------------------------------
// Public API
// ---------------------------------------------------------------------------

/// Extract all files from a single VHD's NTFS filesystem, then delete the VHD.
/// The `output_dir` is where files are extracted to.
pub fn extract_vhd(vhd_path: &Path, output_dir: &Path) -> Result<()> {
    println!("Extracting VHD: {}", vhd_path.display());

    let mut vhd = VhdReader::new(File::open(vhd_path)?).map_err(|e| anyhow!(e))?;
    let prefix = output_dir.file_name().unwrap_or_default().to_string_lossy().to_string();
    extract_ntfs_to_dir(&mut vhd, output_dir, &prefix)?;

    println!("Extracted to: {}", output_dir.display());

    drop(vhd);
    if let Err(e) = std::fs::remove_file(vhd_path) {
        println!("WARNING: Could not delete VHD: {e}");
    }
    Ok(())
}

/// Extract files from a chained view of a base + N differencing VHDs.
///
/// `chain` must be ordered base-first, top-most delta last. A chain of length 1
/// is equivalent to extracting just the base. Unlike [`extract_vhd`], this does
/// **not** delete the inputs — the caller is responsible, since a single VHD
/// in a chain is typically consumed by multiple extractions (one per patch
/// level) and must not be removed until all of them have completed.
pub fn extract_chained_vhd(chain: &[&Path], output_dir: &Path) -> Result<()> {
    if chain.is_empty() {
        return Err(anyhow!("extract_chained_vhd: empty chain"));
    }

    let paths_disp = chain
        .iter()
        .map(|p| p.display().to_string())
        .collect::<Vec<_>>()
        .join(" + ");
    println!("Extracting chained VHD: {paths_disp}");

    let readers: Vec<File> = chain
        .iter()
        .map(|p| File::open(p))
        .collect::<io::Result<_>>()?;
    let mut reader = ChainedVhdReader::new(readers).map_err(|e| anyhow!(e))?;

    let prefix = output_dir.file_name().unwrap_or_default().to_string_lossy().to_string();
    extract_ntfs_to_dir(&mut reader, output_dir, &prefix)?;

    println!("Extracted to: {}", output_dir.display());

    Ok(())
}

// ---------------------------------------------------------------------------
// Helpers
// ---------------------------------------------------------------------------

fn read_be_u32(buf: &[u8], offset: usize) -> u32 {
    u32::from_be_bytes(buf[offset..offset + 4].try_into().unwrap())
}

fn read_be_u64(buf: &[u8], offset: usize) -> u64 {
    u64::from_be_bytes(buf[offset..offset + 8].try_into().unwrap())
}

#[cfg(test)]
mod tests {
    use super::skip_index_entry;
    use ntfs::structured_values::NtfsFileNamespace;

    #[test]
    fn skips_dos_short_name_aliases() {
        // 8.3 aliases duplicate a Win32 entry and must not be extracted again.
        assert!(skip_index_entry(NtfsFileNamespace::Dos, "OXGETH~1.EXE"));
        assert!(skip_index_entry(NtfsFileNamespace::Dos, "PROGRA~1"));
    }

    #[test]
    fn keeps_long_and_native_names() {
        assert!(!skip_index_entry(NtfsFileNamespace::Win32, "oxGetHwInfo.exe"));
        // A name that is its own short name (no separate Dos entry) is kept.
        assert!(!skip_index_entry(NtfsFileNamespace::Win32AndDos, "game.bat"));
        assert!(!skip_index_entry(NtfsFileNamespace::Posix, "readme"));
    }

    #[test]
    fn skips_system_entries_regardless_of_namespace() {
        assert!(skip_index_entry(NtfsFileNamespace::Win32, "$MFT"));
        assert!(skip_index_entry(NtfsFileNamespace::Win32, "System Volume Information"));
        assert!(skip_index_entry(NtfsFileNamespace::Win32, "."));
        assert!(skip_index_entry(NtfsFileNamespace::Win32, ".."));
    }
}