use core::{mem::size_of, ops::Deref};

use bytemuck::{Pod, Zeroable};
use derivative::Derivative;
use num_enum::{FromPrimitive, IntoPrimitive, TryFromPrimitive};
use scroll::{ctx::TryFromCtx, Pread, SizeWith};
use zerocopy::{byteorder::LE, AsBytes, FromBytes, U16, U32, U64};

use crate::{Error, Result};

#[non_exhaustive]
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, FromPrimitive, IntoPrimitive)]
#[repr(u64)]
pub enum KnownObjectId {
    RootTree = 1,
    ExtentTree,
    ChunkTree,
    DevTree,
    FsTree,
    RootTreeDir,
    CsumTree,
    QuotaTree,
    UuidTree,
    FreeSpaceTree,
    __FirstFreeId = 256,
    __LastFreeId = u64::MAX - 256,
    DataRelocTree = u64::MAX - 9,
    TreeReloc = u64::MAX - 8,
    TreeLog = u64::MAX - 7,
    Orphan = u64::MAX - 5,
    #[num_enum(catch_all)]
    Custom(u64),
}

#[repr(C, packed)]
#[derive(Clone, Copy, PartialEq, Eq, FromBytes, AsBytes)]
pub struct ObjectId {
    inner: U64<LE>,
}

impl core::fmt::Debug for ObjectId {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        f.debug_struct("ObjectTypeWrapper")
            .field("inner", &self.as_id())
            .finish()
    }
}

impl ObjectId {
    pub fn from_id(id: KnownObjectId) -> Self {
        Self {
            inner: U64::<LE>::new(id.into()),
        }
    }
    pub fn as_id(self) -> KnownObjectId {
        KnownObjectId::from_primitive(self.inner.get())
    }
}

unsafe impl Pod for ObjectId {}
unsafe impl Zeroable for ObjectId {}

#[repr(u8)]
#[non_exhaustive]
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, FromPrimitive, IntoPrimitive)]
//#[rustc_nonnull_optimization_guaranteed]
pub enum ObjectType {
    INodeItem = 0x01,
    InodeRef = 0x0C,
    InodeExtref = 0x0D,
    XattrItem = 0x18,
    OrphanInode = 0x30,
    DirItem = 0x54,
    DirIndex = 0x60,
    ExtentData = 0x6C,
    ExtentCsum = 0x80,
    RootItem = 0x84,
    TypeRootBackref = 0x90,
    RootRef = 0x9C,
    ExtentItem = 0xA8,
    MetadataItem = 0xA9,
    TreeBlockRef = 0xB0,
    ExtentDataRef = 0xB2,
    ExtentRefV0 = 0xB4,
    SharedBlockRef = 0xB6,
    SharedDataRef = 0xB8,
    BlockGroupItem = 0xC0,
    FreeSpaceInfo = 0xC6,
    FreeSpaceExtent = 0xC7,
    FreeSpaceBitmap = 0xC8,
    DevExtent = 0xCC,
    DevItem = 0xD8,
    ChunkItem = 0xE4,
    TempItem = 0xF8,
    DevStats = 0xF9,
    SubvolUuid = 0xFB,
    SubvolRecUuid = 0xFC,
    #[num_enum(catch_all)]
    Invalid(u8),
}

#[repr(C, packed)]
#[derive(Clone, Copy, PartialEq, Eq, Pread, SizeWith, FromBytes, AsBytes)]
pub struct ObjectTypeWrapper {
    inner: u8,
}

impl core::fmt::Debug for ObjectTypeWrapper {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        write!(f, "{:?}", self.as_type())
    }
}

impl ObjectTypeWrapper {
    pub fn from_ty(ty: ObjectType) -> Self {
        Self { inner: ty.into() }
    }
    pub fn as_type(self) -> ObjectType {
        ObjectType::from_primitive(self.inner)
    }
}

unsafe impl Pod for ObjectTypeWrapper {}
unsafe impl Zeroable for ObjectTypeWrapper {}

#[repr(transparent)]
#[derive(Clone, Copy, PartialEq, Eq, FromBytes, AsBytes)]
pub struct Uuid(uuid::Bytes);

impl core::fmt::Debug for Uuid {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        uuid::Uuid::from_bytes_ref(&self.0).fmt(f)
    }
}

impl Deref for Uuid {
    type Target = uuid::Uuid;

    fn deref(&self) -> &Self::Target {
        uuid::Uuid::from_bytes_ref(&self.0)
    }
}

unsafe impl Pod for Uuid {}
unsafe impl Zeroable for Uuid {}

#[repr(C, packed(1))]
#[derive(Debug, Clone, Copy, Eq, FromBytes, AsBytes)]
pub struct Key {
    pub id: ObjectId,
    pub ty: ObjectTypeWrapper,
    pub offset: U64<LE>,
}

impl Key {
    pub fn new(id: KnownObjectId, ty: ObjectType, offset: u64) -> Self {
        Self {
            id: ObjectId::from_id(id),
            ty: ObjectTypeWrapper::from_ty(ty),
            offset: U64::new(offset),
        }
    }
    pub fn ty(&self) -> ObjectType {
        self.ty.as_type()
    }
    pub fn id(&self) -> KnownObjectId {
        self.id.as_id()
    }
}

impl PartialEq for Key {
    fn eq(&self, other: &Self) -> bool {
        self.id() == other.id() && self.ty() == other.ty() && self.offset == other.offset
    }
}

impl Ord for Key {
    fn cmp(&self, other: &Self) -> core::cmp::Ordering {
        self.partial_cmp(other).unwrap()
    }
}

impl PartialOrd for Key {
    fn partial_cmp(&self, other: &Self) -> Option<core::cmp::Ordering> {
        match self.id().partial_cmp(&other.id()) {
            Some(core::cmp::Ordering::Equal) => {}
            ord => return ord,
        }
        match self.ty().partial_cmp(&other.ty()) {
            Some(core::cmp::Ordering::Equal) => {}
            ord => return ord,
        }
        self.offset.get().partial_cmp(&other.offset.get())
    }
}

macro_rules! impl_try_from_ctx {
    ($($ty:ty),*) => {
        $(impl<'a> TryFromCtx<'a> for $ty {
            type Error = scroll::Error;

            fn try_from_ctx(
                from: &'a [u8],
                _: (),
            ) -> core::result::Result<(Self, usize), Self::Error> {
                Self::read_from(&from[..size_of::<Self>()])
                    .map(|v| (v, size_of::<Self>()))
                    .ok_or(scroll::Error::TooBig {
                        size: size_of::<Self>(),
                        len: from.len(),
                    })
            }
        })*
    };
}

macro_rules! impl_parse_try_from_ctx {
    ($($ty:ty),*) => {
        $(impl $ty {
            pub fn parse(bytes: &[u8]) -> Result<Self> {
                Ok(bytes.pread(0)?)
            }
        })*
    };
}

impl_parse_try_from_ctx!(Chunk, Header, Key, RootItem);
impl_try_from_ctx!(Key, Chunk, Header, Superblock, RootItem);

const MAX_LABEL_SIZE: usize = 0x100;
const SYS_CHUNK_ARRAY_SIZE: usize = 0x800;
const BTRFS_NUM_BACKUP_ROOTS: usize = 4;

fn format_u8str<T: AsRef<[u8]>>(s: &T, f: &mut core::fmt::Formatter) -> core::fmt::Result {
    let bytes = s.as_ref();
    let end = bytes
        .iter()
        .position(|&b| b == 0)
        .map(|i| i + 1)
        .unwrap_or(bytes.len());
    core::ffi::CStr::from_bytes_with_nul(&bytes[..end])
        .map(|s| write!(f, "{:?}", s))
        .map_err(|_| core::fmt::Error)?
}

#[repr(C, packed(1))]
#[derive(Derivative, Clone, Copy, FromBytes, AsBytes)]
#[derivative(Debug)]
pub struct INodeItem {
    generation: U64<LE>,
    transid: U64<LE>,
    st_size: U64<LE>,
    st_blocks: U64<LE>,
    block_group: U64<LE>,
    st_nlink: U32<LE>,
    st_uid: U32<LE>,
    st_gid: U32<LE>,
    st_mode: U32<LE>,
    st_rdev: U64<LE>,
    flags: U64<LE>,
    sequence: U64<LE>,
    #[derivative(Debug = "ignore")]
    reserved: [u8; 32],
    st_atime: Timespec,
    st_ctime: Timespec,
    st_mtime: Timespec,
    otime: Timespec,
}

#[repr(C, packed(1))]
#[derive(Debug, Clone, Copy, Pod, Zeroable)]
pub struct ChunkItem {
    size: u64,
    root_id: u64,
    stripe_length: u64,
    ty: u64,
    opt_io_alignment: u32,
    opt_io_width: u32,
    sector_size: u32,
    num_stripes: u16,
    sub_stripes: u16,
}

#[repr(C, packed(1))]
#[derive(Debug, Clone, Copy, Pod, Zeroable)]
pub struct ChunkItemStripe {
    dev_id: u64,
    offset: u64,
    dev_uuid: Uuid,
}

#[repr(C, packed(1))]
#[derive(Debug, Clone, Copy, Pod, Zeroable)]
pub struct ExtentData {
    generation: u64,
    decoded_size: u64,
    compression: u8,
    encryption: u8,
    encoding: u16,
    ty: u8,
    data: [u8; 1],
}

#[repr(C, packed(1))]
#[derive(Debug, Clone, Copy, Pod, Zeroable)]
pub struct ExtentData2 {
    address: u64,
    size: u64,
    offset: u64,
    num_bytes: u64,
}

#[repr(C, packed(1))]
#[derive(Debug, Clone, Copy, Pod, Zeroable)]
pub struct INodeRef {
    index: u64,
    n: u16,
    name: [u8; 1],
}

#[repr(C, packed(1))]
#[derive(Debug, Clone, Copy, Pod, Zeroable)]
pub struct INodeExtRef {
    dir: u64,
    index: u64,
    n: u16,
    name: [u8; 1],
}

#[repr(C, packed(1))]
#[derive(Debug, Clone, Copy, Pod, Zeroable)]
pub struct ExtentItem {
    ref_count: u64,
    generation: u64,
    flags: u64,
}

#[repr(C, packed(1))]
#[derive(Debug, Clone, Copy)]
pub struct ExtentItem2 {
    first_item: Key,
    level: u8,
}

#[repr(C, packed(1))]
#[derive(Debug, Clone, Copy, Pod, Zeroable)]
pub struct ExtentItemV0 {
    ref_count: u32,
}

#[repr(C, packed(1))]
#[derive(Debug, Clone, Copy)]
pub struct ExtentItemTree {
    extent_item: ExtentItem,
    first_item: Key,
    level: u8,
}

#[repr(C, packed(1))]
#[derive(Debug, Clone, Copy, Pod, Zeroable)]
pub struct TreeBlockRef {
    offset: u64,
}

#[repr(C, packed(1))]
#[derive(Debug, Clone, Copy, Pod, Zeroable)]
pub struct ExtentDataRef {
    root: u64,
    objid: u64,
    offset: u64,
    count: u32,
}

#[repr(C, packed(1))]
#[derive(Debug, Clone, Copy, Pod, Zeroable)]
pub struct BlockGroupItem {
    used: u64,
    chunk_tree: u64,
    flags: u64,
}

#[repr(C, packed(1))]
#[derive(Debug, Clone, Copy, Pod, Zeroable)]
pub struct ExtentRefV0 {
    root: u64,
    gen: u64,
    objid: u64,
    count: u32,
}

#[repr(C, packed(1))]
#[derive(Debug, Clone, Copy, Pod, Zeroable)]
pub struct SharedBlockRef {
    offset: u64,
}

#[repr(C, packed(1))]
#[derive(Debug, Clone, Copy, Pod, Zeroable)]
pub struct SharedDataRef {
    offset: u64,
    count: u32,
}

#[repr(C, packed(1))]
#[derive(Debug, Clone, Copy, Pod, Zeroable)]
pub struct FreeSpaceEntry {
    offset: u64,
    size: u64,
    ty: u8,
}

#[repr(C, packed(1))]
#[derive(Debug, Clone, Copy)]
pub struct FreeSpaceItem {
    key: Key,

    generation: u64,
    num_entries: u64,
    num_bitmaps: u64,
}

#[repr(C, packed(1))]
#[derive(Debug, Clone, Copy, Pod, Zeroable)]
pub struct RootRef {
    dir: u64,
    index: u64,
    n: u16,
    name: [u8; 1],
}

#[repr(C, packed(1))]
#[derive(Debug, Clone, Copy, Pod, Zeroable)]
pub struct DevExtent {
    chunktree: u64,
    objid: u64,
    address: u64,
    length: u64,
    chunktree_uuid: Uuid,
}

#[repr(C, packed(1))]
#[derive(Debug, Clone, Copy, Pod, Zeroable)]
pub struct BalanceArgs {}

#[repr(C, packed(1))]
#[derive(Debug, Clone, Copy, Pod, Zeroable)]
pub struct BalanceItem {}

#[repr(C, packed(1))]
#[derive(Debug, Clone, Copy, Pod, Zeroable)]
pub struct FreeSpaceInfo {
    count: u32,
    flags: u32,
}

#[repr(C, packed(1))]
#[derive(Debug, Clone, Copy, Pod, Zeroable)]
pub struct SendHeader {}
#[repr(C, packed(1))]
#[derive(Debug, Clone, Copy, Pod, Zeroable)]
pub struct SendCommand {}
#[repr(C, packed(1))]
#[derive(Debug, Clone, Copy, Pod, Zeroable)]
pub struct SendTlv {}

const CSUM_SIZE: usize = 32;
const LABEL_SIZE: usize = 256;
const SYSTEM_CHUNK_ARRAY_SIZE: usize = 2048;

pub const FS_TREE_OBJECTID: u64 = 5;

pub const INODE_REF_KEY: u8 = 12;
pub const DIR_ITEM_KEY: u8 = 84;
pub const ROOT_ITEM_KEY: u8 = 132;
pub const CHUNK_ITEM_KEY: u8 = 228;

pub const FT_REG_FILE: u8 = 1;

#[repr(C, packed)]
#[derive(Debug, Clone, Copy, FromBytes, AsBytes)]
pub struct DevItem {
    /// the internal btrfs device id
    pub devid: U64<LE>,
    /// size of the device
    pub total_bytes: U64<LE>,
    /// bytes used
    pub bytes_used: U64<LE>,
    /// optimal io alignment for this device
    pub io_align: U32<LE>,
    /// optimal io width for this device
    pub io_width: U32<LE>,
    /// minimal io size for this device
    pub sector_size: U32<LE>,
    /// type and info about this device
    pub ty: U64<LE>,
    /// expected generation for this device
    pub generation: U64<LE>,
    /// starting byte of this partition on the device, to allow for stripe alignment in the future
    pub start_offset: U64<LE>,
    /// grouping information for allocation decisions
    pub dev_group: U32<LE>,
    /// seek speed 0-100 where 100 is fastest
    pub seek_speed: u8,
    /// bandwidth 0-100 where 100 is fastest
    pub bandwidth: u8,
    /// btrfs generated uuid for this device
    pub uuid: Uuid,
    /// uuid of FS who owns this device
    pub fsid: Uuid,
}

#[repr(C, packed)]
#[derive(Debug, Clone, Copy, FromBytes, AsBytes)]
pub struct RootBackup {
    pub tree_root: U64<LE>,
    pub tree_root_gen: U64<LE>,
    pub chunk_root: U64<LE>,
    pub chunk_root_gen: U64<LE>,
    pub extent_root: U64<LE>,
    pub extent_root_gen: U64<LE>,
    pub fs_root: U64<LE>,
    pub fs_root_gen: U64<LE>,
    pub dev_root: U64<LE>,
    pub dev_root_gen: U64<LE>,
    pub csum_root: U64<LE>,
    pub csum_root_gen: U64<LE>,
    pub total_bytes: U64<LE>,
    pub bytes_used: U64<LE>,
    pub num_devices: U64<LE>,
    /// future
    pub unused_64: [u64; 4],
    pub tree_root_level: u8,
    pub chunk_root_level: u8,
    pub extent_root_level: u8,
    pub fs_root_level: u8,
    pub dev_root_level: u8,
    pub csum_root_level: u8,
    /// future and to align
    pub unused_8: [u8; 10],
}

#[repr(C, packed)]
#[derive(Derivative, Clone, Copy, FromBytes, AsBytes)]
#[derivative(Debug)]
pub struct Superblock {
    pub csum: [u8; 32],
    pub fsid: Uuid,
    /// Physical address of this block
    pub bytenr: U64<LE>,
    pub flags: U64<LE>,
    pub magic: [u8; 0x8],
    pub generation: U64<LE>,
    /// Logical address of the root tree root
    pub root: U64<LE>,
    /// Logical address of the chunk tree root
    pub chunk_root: U64<LE>,
    /// Logical address of the log tree root
    pub log_root: U64<LE>,
    pub log_root_transid: U64<LE>,
    pub total_bytes: U64<LE>,
    pub bytes_used: U64<LE>,
    pub root_dir_objectid: U64<LE>,
    pub num_devices: U64<LE>,
    pub sector_size: U32<LE>,
    pub node_size: U32<LE>,
    /// Unused and must be equal to `nodesize`
    pub leafsize: U32<LE>,
    pub stripesize: U32<LE>,
    pub sys_chunk_array_size: U32<LE>,
    pub chunk_root_generation: U64<LE>,
    pub compat_flags: U64<LE>,
    pub compat_ro_flags: U64<LE>,
    pub incompat_flags: U64<LE>,
    pub csum_type: U16<LE>,
    pub root_level: u8,
    pub chunk_root_level: u8,
    pub log_root_level: u8,
    pub dev_item: DevItem,
    #[derivative(Debug(format_with = "format_u8str"))]
    pub label: [u8; 0x100],
    pub cache_generation: U64<LE>,
    pub uuid_tree_generation: U64<LE>,
    pub metadata_uuid: Uuid,
    /// Future expansion
    #[derivative(Debug = "ignore")]
    _reserved: [u64; 28],
    #[derivative(Debug = "ignore")]
    pub sys_chunk_array: [u8; 0x800],
    #[derivative(Debug = "ignore")]
    pub root_backups: [RootBackup; 4],
    #[derivative(Debug = "ignore")]
    _reserved2: [u8; 565],
}

#[repr(u16)]
#[derive(Derivative, Clone, Copy, TryFromPrimitive)]
#[derivative(Debug)]
pub enum ChecksumType {
    Crc32 = 0,
    XxHash64,
    Sha256,
    Blake2B,
}

pub fn calculate_crc32c(bytes: &[u8]) -> [u8; 32] {
    let crc = crc::Crc::<u32>::new(&crc::CRC_32_ISCSI);
    let mut csum = [0u8; 32];
    csum[..4].copy_from_slice(crc.checksum(bytes).as_bytes());
    csum
}

impl Superblock {
    pub const SUPERBLOCK_BASE_OFFSET: usize = 0x10000;
    pub const SUPERBLOCK_OFFSETS: [usize; 4] = [
        Self::SUPERBLOCK_BASE_OFFSET,
        0x4000000,
        0x4000000000,
        0x4000000000000,
    ];
    pub const MAGIC: [u8; 8] = *b"_BHRfS_M";

    pub fn parse(bytes: &[u8]) -> Result<Self> {
        let superblock = Self::read_from(bytes).ok_or(Error::ReadFailed)?;

        if !superblock.verify_magic() {
            return Err(Error::InvalidMagic);
        }

        if !superblock.verify_checksum() {
            return Err(Error::InvalidChecksum {
                expected: superblock.csum,
                actual: superblock.calculate_checksum(),
            });
        }

        Ok(superblock)
    }

    pub fn calculate_checksum(&self) -> [u8; 32] {
        match self.checksum_type().expect("csum type invalid") {
            ChecksumType::Crc32 => calculate_crc32c(&self.as_bytes()[0x20..]),
            ChecksumType::XxHash64 => todo!(),
            ChecksumType::Sha256 => todo!(),
            ChecksumType::Blake2B => todo!(),
        }
    }

    pub fn verify_checksum(&self) -> bool {
        self.calculate_checksum() == self.csum
    }

    pub fn checksum_type(&self) -> Option<ChecksumType> {
        ChecksumType::try_from_primitive(self.csum_type.get()).ok()
    }

    pub fn verify_magic(&self) -> bool {
        self.magic == Self::MAGIC
    }
}

#[repr(C, packed)]
#[derive(Debug, Clone, Copy, FromBytes, AsBytes)]
pub struct Stripe {
    pub devid: U64<LE>,
    pub offset: U64<LE>,
    pub dev_uuid: Uuid,
}

impl Stripe {
    pub fn parse(bytes: &[u8]) -> Result<Self> {
        Self::read_from(bytes).ok_or(Error::ReadFailed)
    }
}

#[repr(C, packed)]
#[derive(Debug, Clone, Copy, FromBytes, AsBytes)]
pub struct Chunk {
    /// size of this chunk in bytes
    pub length: U64<LE>,
    /// objectid of the root referencing this chunk
    pub owner: U64<LE>,
    pub stripe_len: U64<LE>,
    pub ty: U64<LE>,
    /// optimal io alignment for this chunk
    pub io_align: U32<LE>,
    /// optimal io width for this chunk
    pub io_width: U32<LE>,
    /// minimal io size for this chunk
    pub sector_size: U32<LE>,
    /// 2^16 stripes is quite a lot, a second limit is the size of a single item in the btree
    pub num_stripes: U16<LE>,
    /// sub stripes only matter for raid10
    pub sub_stripes: U16<LE>,
    pub stripe: Stripe,
    // additional stripes go here
}

#[repr(C, packed)]
#[derive(Debug, Clone, Copy, FromBytes, AsBytes)]
pub struct Timespec {
    pub sec: U64<LE>,
    pub nsec: U32<LE>,
}

#[repr(C, packed)]
#[derive(Derivative, Clone, Copy, FromBytes, AsBytes)]
#[derivative(Debug)]
pub struct InodeItem {
    /// nfs style generation number
    pub generation: U64<LE>,
    /// transid that last touched this inode
    pub transid: U64<LE>,
    pub size: U64<LE>,
    pub nbytes: U64<LE>,
    pub block_group: U64<LE>,
    pub nlink: U32<LE>,
    pub uid: U32<LE>,
    pub gid: U32<LE>,
    pub mode: U32<LE>,
    pub rdev: U64<LE>,
    pub flags: U64<LE>,
    /// modification sequence number for NFS
    pub sequence: U64<LE>,
    #[derivative(Debug = "ignore")]
    pub reserved: [u64; 4],
    pub atime: Timespec,
    pub ctime: Timespec,
    pub mtime: Timespec,
    pub otime: Timespec,
}

#[repr(C, packed)]
#[derive(Derivative, Clone, Copy, FromBytes, AsBytes)]
#[derivative(Debug)]
pub struct RootItem {
    pub inode: InodeItem,
    pub generation: U64<LE>,
    pub root_dirid: U64<LE>,
    pub bytenr: U64<LE>,
    pub byte_limit: U64<LE>,
    pub bytes_used: U64<LE>,
    pub last_snapshot: U64<LE>,
    pub flags: U64<LE>,
    pub refs: U32<LE>,
    pub drop_progress: Key,
    pub drop_level: u8,
    pub level: u8,
    pub generation_v2: U64<LE>,
    pub uuid: Uuid,
    pub parent_uuid: Uuid,
    pub received_uuid: Uuid,
    /// updated when an inode changes
    pub ctransid: U64<LE>,
    /// trans when created
    pub otransid: U64<LE>,
    /// trans when sent. non-zero for received subvol
    pub stransid: U64<LE>,
    /// trans when received. non-zero for received subvol
    pub rtransid: U64<LE>,
    pub ctime: Timespec,
    pub otime: Timespec,
    pub stime: Timespec,
    pub rtime: Timespec,
    #[derivative(Debug = "ignore")]
    pub reserved: [u64; 8],
}

#[repr(u8)]
#[non_exhaustive]
#[derive(Debug, Clone, Copy, PartialEq, Eq, FromPrimitive)]
pub enum DirItemType {
    Unknown,
    RegFile,
    Dir,
    ChrDev,
    BlkDev,
    Fifo,
    Sock,
    Symlink,
    Xattr,
    #[num_enum(catch_all)]
    Invalid(u8),
}

#[repr(C, packed)]
#[derive(Debug, Clone, Copy, FromBytes, AsBytes)]
pub struct DirItem {
    pub location: Key,
    pub transid: U64<LE>,
    pub data_len: U16<LE>,
    pub name_len: U16<LE>,
    ty: u8,
}

impl DirItem {
    pub fn ty(&self) -> DirItemType {
        DirItemType::from_primitive(self.ty)
    }

    pub fn parse_single(bytes: &[u8]) -> Result<(DirItemEntry)> {
        let offset = &mut 0;
        Self::parse_single_inner(bytes, offset)
    }

    fn parse_single_inner(bytes: &[u8], offset: &mut usize) -> Result<DirItemEntry> {
        let dir_item = DirItem::read_from(&bytes[*offset..*offset + size_of::<DirItem>()])
            .ok_or(Error::ReadFailed)?;
        *offset += size_of::<DirItem>();
        let name_len = dir_item.name_len.get() as usize;
        let name = &bytes[*offset..*offset + name_len];
        *offset += name_len;

        Ok(DirItemEntry::new(dir_item, name.to_vec()))
    }

    pub fn parse(bytes: &[u8]) -> Result<Vec<(DirItemEntry)>> {
        let offset = &mut 0;
        let entries = core::iter::from_fn(|| {
            if *offset + size_of::<DirItem>() < bytes.len() {
                Some(Self::parse_single_inner(&bytes[*offset..], offset))
            } else {
                None
            }
        })
        .collect::<Result<Vec<_>>>()?;

        Ok(entries)
    }
}

#[derive(Clone)]
pub struct DirItemEntry {
    pub dir_item: DirItem,
    pub name: Vec<u8>,
}

impl DirItemEntry {
    pub fn new(dir_item: DirItem, name: Vec<u8>) -> Self {
        Self { dir_item, name }
    }

    pub fn name_as_str(&self) -> core::result::Result<&str, core::str::Utf8Error> {
        core::str::from_utf8(&self.name)
    }
    pub fn name_as_string_lossy(&self) -> alloc::borrow::Cow<str> {
        alloc::string::String::from_utf8_lossy(&self.name)
    }
}

impl core::fmt::Debug for DirItemEntry {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        f.debug_struct("DirItemEntry")
            .field("dir_item", &self.dir_item)
            .field("name", &self.name_as_string_lossy())
            .finish()
    }
}

#[repr(C, packed)]
#[derive(Debug, Clone, Copy, Pod, Zeroable)]
pub struct InodeRef {
    pub index: u64,
    pub name_len: u16,
}

#[repr(C, packed)]
#[derive(Debug, Clone, PartialEq, Eq, Copy, FromBytes, AsBytes)]
pub struct Header {
    pub csum: [u8; 32],
    pub fsid: Uuid,
    /// Which block this node is supposed to live in
    pub bytenr: U64<LE>,
    pub flags: U64<LE>,
    pub chunk_tree_uuid: Uuid,
    pub generation: U64<LE>,
    pub owner: U64<LE>,
    pub nritems: U32<LE>,
    pub level: u8,
}

#[repr(C, packed)]
#[derive(Debug, Clone, Copy, FromBytes, AsBytes)]
/// A `BtrfsLeaf` is full of `BtrfsItem`s. `offset` and `size` (relative to start of data area)
/// tell us where to find the item in the leaf.
pub struct Item {
    pub key: Key,
    pub offset: U32<LE>,
    pub size: U32<LE>,
}

#[repr(C, packed)]
#[derive(Debug, Clone, Copy, FromBytes, AsBytes)]
/// All non-leaf blocks are nodes and they hold only keys are pointers to other blocks
pub struct KeyPtr {
    pub key: Key,
    pub blockptr: U64<LE>,
    pub generation: U64<LE>,
}

use alloc::vec::Vec;

#[derive(Debug)]
pub enum TreeItem {
    Chunk(Chunk),
    Root(RootItem),
    DirItem(Vec<DirItemEntry>),
    DirIndex(DirItemEntry),
    Unimplemented,
}

impl From<Chunk> for TreeItem {
    fn from(value: Chunk) -> Self {
        Self::Chunk(value)
    }
}

impl From<RootItem> for TreeItem {
    fn from(value: RootItem) -> Self {
        Self::Root(value)
    }
}

impl From<Vec<DirItemEntry>> for TreeItem {
    fn from(value: Vec<DirItemEntry>) -> Self {
        Self::DirItem(value)
    }
}

impl From<DirItemEntry> for TreeItem {
    fn from(value: DirItemEntry) -> Self {
        Self::DirIndex(value)
    }
}

impl TreeItem {
    pub fn parse(item: &Item, bytes: &[u8]) -> Result<Self> {
        Ok(match item.key.ty() {
            ObjectType::RootItem => RootItem::parse(bytes)?.into(),
            ObjectType::ChunkItem => Chunk::parse(bytes)?.into(),
            ObjectType::DirItem => DirItem::parse(bytes)?.into(),
            ObjectType::DirIndex => DirItem::parse_single(bytes)?.into(),
            _ => TreeItem::Unimplemented,
        })
    }
}

impl TreeItem {
    pub fn as_chunk(&self) -> Option<&Chunk> {
        if let Self::Chunk(v) = self {
            Some(v)
        } else {
            None
        }
    }

    pub fn as_root(&self) -> Option<&RootItem> {
        if let Self::Root(v) = self {
            Some(v)
        } else {
            None
        }
    }
}

#[derive(Debug, Clone)]
pub struct BTreeLeafNode {
    pub header: Header,
    /// actual leaf data
    pub items: Vec<Item>,
}

impl BTreeLeafNode {
    pub fn parse(header: Header, bytes: &[u8]) -> Result<Self> {
        log::debug!("leaf:");

        let offset = &mut 0;
        let items = core::iter::from_fn(|| {
            if *offset as usize + size_of::<Item>() < bytes.len() {
                let item = Item::read_from(&bytes[*offset..*offset + size_of::<Item>()]);
                *offset += size_of::<Item>();

                if let Some(item) = item.as_ref() {
                    log::debug!(
                        "\titem type {:?}: ty offset: {}",
                        item.key.ty.as_type(),
                        item.key.offset.get()
                    );
                    log::debug!("\t{item:?}");
                }

                item
            } else {
                None
            }
        })
        .take(header.nritems.get() as usize)
        .collect::<Vec<_>>();
        Ok(Self { header, items })
    }
}

#[derive(Debug, Clone)]
pub struct BTreeInternalNode {
    pub header: Header,
    pub children: Vec<KeyPtr>,
}

impl BTreeInternalNode {
    pub fn parse(header: Header, bytes: &[u8]) -> Result<Self> {
        log::debug!("internal lvl: {}", header.level);

        let offset = &mut 0;
        let size = size_of::<KeyPtr>();
        let children = core::iter::from_fn(|| {
            if *offset as usize + size < bytes.len() {
                let item = KeyPtr::read_from(&bytes[*offset..*offset + size]);
                *offset += size;

                if let Some(item) = item.as_ref() {
                    log::debug!(
                        "\tchild gen: {} offset: {}",
                        item.generation.get(),
                        item.key.offset.get()
                    );
                }

                item
            } else {
                None
            }
        })
        .take(header.nritems.get() as usize)
        .collect::<Vec<_>>();

        Ok(Self { header, children })
    }
}

#[derive(Debug, Clone)]
pub enum BTreeNode {
    Internal(BTreeInternalNode),
    Leaf(BTreeLeafNode),
}

impl BTreeNode {
    pub fn parse(bytes: &[u8]) -> Result<Self> {
        let offset = &mut 0;
        let header = bytes.gread::<Header>(offset)?;

        if header.level == 0 {
            Ok(Self::Leaf(BTreeLeafNode::parse(header, &bytes[*offset..])?))
        } else {
            Ok(Self::Internal(BTreeInternalNode::parse(
                header,
                &bytes[*offset..],
            )?))
        }
    }
}