//! The "version 2" disk representation of the dirstate

//!

//! See `mercurial/helptext/internals/dirstate-v2.txt`

use crate::dirstate::{DirstateV2Data, TruncatedTimestamp};

use crate::dirstate_tree::dirstate_map::DirstateVersion;

use crate::dirstate_tree::dirstate_map::{

    self, DirstateMap, DirstateMapWriteMode, NodeRef,

};

use crate::dirstate_tree::path_with_basename::WithBasename;

use crate::errors::HgError;

use crate::utils::hg_path::HgPath;

use crate::DirstateEntry;

use crate::DirstateError;

use crate::DirstateParents;

use bitflags::bitflags;

use bytes_cast::unaligned::{U16Be, U32Be};

use bytes_cast::BytesCast;

use format_bytes::format_bytes;

use rand::Rng;

use std::borrow::Cow;

use std::fmt::Write;

/// Added at the start of `.hg/dirstate` when the "v2" format is used.

/// This a redundant sanity check more than an actual "magic number" since

/// `.hg/requires` already governs which format should be used.

pub const V2_FORMAT_MARKER: &[u8; 12] = b"dirstate-v2\n";

/// Keep space for 256-bit hashes

const STORED_NODE_ID_BYTES: usize = 32;

/// … even though only 160 bits are used for now, with SHA-1

const USED_NODE_ID_BYTES: usize = 20;

pub(super) const IGNORE_PATTERNS_HASH_LEN: usize = 20;

pub(super) type IgnorePatternsHash = [u8; IGNORE_PATTERNS_HASH_LEN];

/// Must match constants of the same names in `mercurial/dirstateutils/v2.py`

const TREE_METADATA_SIZE: usize = 44;

const NODE_SIZE: usize = 44;

/// Make sure that size-affecting changes are made knowingly

#[allow(unused)]

fn static_assert_size_of() {

    let _ = std::mem::transmute::<TreeMetadata, [u8; TREE_METADATA_SIZE]>;

    let _ = std::mem::transmute::<DocketHeader, [u8; TREE_METADATA_SIZE + 81]>;

    let _ = std::mem::transmute::<Node, [u8; NODE_SIZE]>;

}

// Must match `HEADER` in `mercurial/dirstateutils/docket.py`

#[derive(BytesCast)]

#[repr(C)]

struct DocketHeader {

    marker: [u8; V2_FORMAT_MARKER.len()],

    parent_1: [u8; STORED_NODE_ID_BYTES],

    parent_2: [u8; STORED_NODE_ID_BYTES],

    metadata: TreeMetadata,

    /// Counted in bytes

    data_size: Size,

    uuid_size: u8,

}

pub struct Docket<'on_disk> {

    header: &'on_disk DocketHeader,

    pub uuid: &'on_disk [u8],

}

/// Fields are documented in the *Tree metadata in the docket file*

/// section of `mercurial/helptext/internals/dirstate-v2.txt`

#[derive(BytesCast)]

#[repr(C)]

pub struct TreeMetadata {

    root_nodes: ChildNodes,

    nodes_with_entry_count: Size,

    nodes_with_copy_source_count: Size,

    unreachable_bytes: Size,

    unused: [u8; 4],

    /// See *Optional hash of ignore patterns* section of

    /// `mercurial/helptext/internals/dirstate-v2.txt`

    ignore_patterns_hash: IgnorePatternsHash,

}

/// Fields are documented in the *The data file format*

/// section of `mercurial/helptext/internals/dirstate-v2.txt`

#[derive(BytesCast, Debug)]

#[repr(C)]

pub(super) struct Node {

    full_path: PathSlice,

    /// In bytes from `self.full_path.start`

    base_name_start: PathSize,

    copy_source: OptPathSlice,

    children: ChildNodes,

    pub(super) descendants_with_entry_count: Size,

    pub(super) tracked_descendants_count: Size,

    flags: U16Be,

    size: U32Be,

    mtime: PackedTruncatedTimestamp,

}

bitflags! {

    #[repr(C)]

    struct Flags: u16 {

        const WDIR_TRACKED = 1 << 0;

        const P1_TRACKED = 1 << 1;

        const P2_INFO = 1 << 2;

        const MODE_EXEC_PERM = 1 << 3;

        const MODE_IS_SYMLINK = 1 << 4;

        const HAS_FALLBACK_EXEC = 1 <<  5;

        const FALLBACK_EXEC = 1 <<  6;

        const HAS_FALLBACK_SYMLINK = 1 <<  7;

        const FALLBACK_SYMLINK = 1 <<  8;

        const EXPECTED_STATE_IS_MODIFIED = 1 << 9;

        const HAS_MODE_AND_SIZE = 1 <<10;

        const HAS_MTIME = 1 <<11;

        const MTIME_SECOND_AMBIGUOUS = 1 << 12;

        const DIRECTORY = 1 <<13;

        const ALL_UNKNOWN_RECORDED = 1 <<14;

        const ALL_IGNORED_RECORDED = 1 <<15;

    }

}

/// Duration since the Unix epoch

#[derive(BytesCast, Copy, Clone, Debug)]

#[repr(C)]

struct PackedTruncatedTimestamp {

    truncated_seconds: U32Be,

    nanoseconds: U32Be,

}

/// Counted in bytes from the start of the file

///

/// NOTE: not supporting `.hg/dirstate` files larger than 4 GiB.

type Offset = U32Be;

/// Counted in number of items

///

/// NOTE: we choose not to support counting more than 4 billion nodes anywhere.

type Size = U32Be;

/// Counted in bytes

///

/// NOTE: we choose not to support file names/paths longer than 64 KiB.

type PathSize = U16Be;

/// A contiguous sequence of `len` times `Node`, representing the child nodes

/// of either some other node or of the repository root.

///

/// Always sorted by ascending `full_path`, to allow binary search.

/// Since nodes with the same parent nodes also have the same parent path,

/// only the `base_name`s need to be compared during binary search.

#[derive(BytesCast, Copy, Clone, Debug)]

#[repr(C)]

struct ChildNodes {

    start: Offset,

    len: Size,

}

/// A `HgPath` of `len` bytes

#[derive(BytesCast, Copy, Clone, Debug)]

#[repr(C)]

struct PathSlice {

    start: Offset,

    len: PathSize,

}

/// Either nothing if `start == 0`, or a `HgPath` of `len` bytes

type OptPathSlice = PathSlice;

/// Unexpected file format found in `.hg/dirstate` with the "v2" format.

///

/// This should only happen if Mercurial is buggy or a repository is corrupted.

#[derive(Debug)]

pub struct DirstateV2ParseError {

    message: String,

}

impl DirstateV2ParseError {

    pub fn new<S: Into<String>>(message: S) -> Self {

        Self {

            message: message.into(),

        }

    }

}

impl From<DirstateV2ParseError> for HgError {

    fn from(e: DirstateV2ParseError) -> Self {

        HgError::corrupted(format!("dirstate-v2 parse error: {}", e.message))

    }

}

impl From<DirstateV2ParseError> for crate::DirstateError {

    fn from(error: DirstateV2ParseError) -> Self {

        HgError::from(error).into()

    }

}

impl TreeMetadata {

    pub fn as_bytes(&self) -> &[u8] {

        BytesCast::as_bytes(self)

    }

}

impl<'on_disk> Docket<'on_disk> {

    /// Generate the identifier for a new data file

    ///

    /// TODO: support the `HGTEST_UUIDFILE` environment variable.

    /// See `mercurial/revlogutils/docket.py`

    pub fn new_uid() -> String {

        const ID_LENGTH: usize = 8;

        let mut id = String::with_capacity(ID_LENGTH);

        let mut rng = rand::thread_rng();

        for _ in 0..ID_LENGTH {

            // One random hexadecimal digit.

            // `unwrap` never panics because `impl Write for String`

            // never returns an error.

            write!(&mut id, "{:x}", rng.gen_range(0..16)).unwrap();

        }

        id

    }

    pub fn serialize(

        parents: DirstateParents,

        tree_metadata: TreeMetadata,

        data_size: u64,

        uuid: &[u8],

    ) -> Result<Vec<u8>, std::num::TryFromIntError> {

        let header = DocketHeader {

            marker: *V2_FORMAT_MARKER,

            parent_1: parents.p1.pad_to_256_bits(),

            parent_2: parents.p2.pad_to_256_bits(),

            metadata: tree_metadata,

            data_size: u32::try_from(data_size)?.into(),

            uuid_size: uuid.len().try_into()?,

        };

        let header = header.as_bytes();

        let mut docket = Vec::with_capacity(header.len() + uuid.len());

        docket.extend_from_slice(header);

        docket.extend_from_slice(uuid);

        Ok(docket)

    }

    pub fn parents(&self) -> DirstateParents {

        use crate::Node;

        let p1 = Node::try_from(&self.header.parent_1[..USED_NODE_ID_BYTES])

            .unwrap();

        let p2 = Node::try_from(&self.header.parent_2[..USED_NODE_ID_BYTES])

            .unwrap();

        DirstateParents { p1, p2 }

    }

    pub fn tree_metadata(&self) -> &[u8] {

        self.header.metadata.as_bytes()

    }

    pub fn data_size(&self) -> usize {

        // This `unwrap` could only panic on a 16-bit CPU

        self.header.data_size.get().try_into().unwrap()

    }

    pub fn data_filename(&self) -> String {

        String::from_utf8(format_bytes!(b"dirstate.{}", self.uuid)).unwrap()

    }

}

pub fn read_docket(

    on_disk: &[u8],

) -> Result<Docket<'_>, DirstateV2ParseError> {

    let (header, uuid) = DocketHeader::from_bytes(on_disk).map_err(|e| {

        DirstateV2ParseError::new(format!("when reading docket, {}", e))

    })?;

    let uuid_size = header.uuid_size as usize;

    if header.marker == *V2_FORMAT_MARKER && uuid.len() == uuid_size {

        Ok(Docket { header, uuid })

    } else {

        Err(DirstateV2ParseError::new(

            "invalid format marker or uuid size",

        ))

    }

}

pub(super) fn read<'on_disk>(

    on_disk: &'on_disk [u8],

    metadata: &[u8],

    uuid: Vec<u8>,

    identity: Option<u64>,

) -> Result<DirstateMap<'on_disk>, DirstateV2ParseError> {

    if on_disk.is_empty() {

        let mut map = DirstateMap::empty(on_disk);

        map.dirstate_version = DirstateVersion::V2;

        return Ok(map);

    }

    let (meta, _) = TreeMetadata::from_bytes(metadata).map_err(|e| {

        DirstateV2ParseError::new(format!("when parsing tree metadata, {}", e))

    })?;

    let dirstate_map = DirstateMap {

        on_disk,

        root: dirstate_map::ChildNodes::OnDisk(

            read_nodes(on_disk, meta.root_nodes).map_err(|mut e| {

                e.message = format!("{}, when reading root notes", e.message);

                e

            })?,

        ),

        nodes_with_entry_count: meta.nodes_with_entry_count.get(),

        nodes_with_copy_source_count: meta.nodes_with_copy_source_count.get(),

        ignore_patterns_hash: meta.ignore_patterns_hash,

        unreachable_bytes: meta.unreachable_bytes.get(),

        old_data_size: on_disk.len(),

        old_uuid: Some(uuid),

        identity,

        dirstate_version: DirstateVersion::V2,

        write_mode: DirstateMapWriteMode::Auto,

    };

    Ok(dirstate_map)

}

impl Node {

    pub(super) fn full_path<'on_disk>(

        &self,

        on_disk: &'on_disk [u8],

    ) -> Result<&'on_disk HgPath, DirstateV2ParseError> {

        read_hg_path(on_disk, self.full_path)

    }

    pub(super) fn base_name_start(

        &self,

    ) -> Result<usize, DirstateV2ParseError> {

        let start = self.base_name_start.get();

        if start < self.full_path.len.get() {

            let start = usize::try_from(start)

                // u32 -> usize, could only panic on a 16-bit CPU

                .expect("dirstate-v2 base_name_start out of bounds");

            Ok(start)

        } else {

            Err(DirstateV2ParseError::new("not enough bytes for base name"))

        }

    }

    pub(super) fn base_name<'on_disk>(

        &self,

        on_disk: &'on_disk [u8],

    ) -> Result<&'on_disk HgPath, DirstateV2ParseError> {

        let full_path = self.full_path(on_disk)?;