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

//!

//! # File format

//!

//! The file starts with a fixed-sized header, whose layout is defined by the

//! `Header` struct. Its `root` field contains the slice (offset and length) to

//! the nodes representing the files and directories at the root of the

//! repository. Each node is also fixed-size, defined by the `Node` struct.

//! Nodes in turn contain slices to variable-size paths, and to their own child

//! nodes (if any) for nested files and directories.

use crate::dirstate_tree::dirstate_map::{self, DirstateMap, 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 crate::EntryState;

use bytes_cast::unaligned::{I32Be, I64Be, U32Be, U64Be};

use bytes_cast::BytesCast;

use std::borrow::Cow;

use std::convert::TryFrom;

use std::time::{Duration, SystemTime, UNIX_EPOCH};

/// 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";

#[derive(BytesCast)]

#[repr(C)]

struct Header {

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

    /// `dirstatemap.parents()` in `mercurial/dirstate.py` relies on this

    /// `parents` field being at this offset, immediately after `marker`.

    parents: DirstateParents,

    root: ChildNodes,

    nodes_with_entry_count: Size,

    nodes_with_copy_source_count: Size,

}

#[derive(BytesCast)]

#[repr(C)]

pub(super) struct Node {

    full_path: PathSlice,

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

    base_name_start: Size,

    copy_source: OptPathSlice,

    children: ChildNodes,

    pub(super) tracked_descendants_count: Size,

    /// Dependending on the value of `state`:

    ///

    /// * A null byte: `data` is not used.

    ///

    /// * A `n`, `a`, `r`, or `m` ASCII byte: `state` and `data` together

    ///   represent a dirstate entry like in the v1 format.

    ///

    /// * A `d` ASCII byte: the bytes of `data` should instead be interpreted

    ///   as the `Timestamp` for the mtime of a cached directory.

    ///

    ///   The presence of this state means that at some point, this path in

    ///   the working directory was observed:

    ///

    ///   - To be a directory

    ///   - With the modification time as given by `Timestamp`

    ///   - That timestamp was already strictly in the past when observed,

    ///     meaning that later changes cannot happen in the same clock tick

    ///     and must cause a different modification time (unless the system

    ///     clock jumps back and we get unlucky, which is not impossible but

    ///     but deemed unlikely enough).

    ///   - The directory did not contain any child entry that did not have a

    ///     corresponding dirstate node.

    ///

    ///   This means that if `std::fs::symlink_metadata` later reports the

    ///   same modification time, we don’t need to call `std::fs::read_dir`

    ///   again for this directory and can iterate child dirstate nodes

    ///   instead.

    state: u8,

    data: Entry,

}

#[derive(BytesCast, Copy, Clone)]

#[repr(C)]

struct Entry {

    mode: I32Be,

    mtime: I32Be,

    size: I32Be,

}

/// Duration since the Unix epoch

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

#[repr(C)]

pub(super) struct Timestamp {

    seconds: I64Be,

    /// In `0 .. 1_000_000_000`.

    ///

    /// This timestamp is later or earlier than `(seconds, 0)` by this many

    /// nanoseconds, if `seconds` is non-negative or negative, respectively.

    nanoseconds: U32Be,

}

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

///

/// NOTE: If we decide to never support `.hg/dirstate` files larger than 4 GiB

/// we could save space by using `U32Be` instead.

type Offset = U64Be;

/// Counted in number of items

///

/// NOTE: not supporting directories with more than 4 billion direct children,

/// or filenames more than 4 GiB.

type Size = U32Be;

/// Location of consecutive, fixed-size items.

///

/// An item can be a single byte for paths, or a struct with

/// `derive(BytesCast)`.

#[derive(BytesCast, Copy, Clone)]

#[repr(C)]

struct Slice {

    start: Offset,

    len: Size,

}

/// 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.

type ChildNodes = Slice;

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

type PathSlice = Slice;

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

type OptPathSlice = Slice;

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

fn _static_assert_size_of() {

    let _ = std::mem::transmute::<Header, [u8; 72]>;

    let _ = std::mem::transmute::<Node, [u8; 57]>;

}

/// 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;

impl From<DirstateV2ParseError> for HgError {

    fn from(_: DirstateV2ParseError) -> Self {

        HgError::corrupted("dirstate-v2 parse error")

    }

}

impl From<DirstateV2ParseError> for crate::DirstateError {

    fn from(error: DirstateV2ParseError) -> Self {

        HgError::from(error).into()

    }

}

pub(super) fn read<'on_disk>(

    on_disk: &'on_disk [u8],

) -> Result<

    (DirstateMap<'on_disk>, Option<DirstateParents>),

    DirstateV2ParseError,

> {

    if on_disk.is_empty() {

        return Ok((DirstateMap::empty(on_disk), None));

    }

    let dirstate_map = DirstateMap {

        on_disk,

        root: dirstate_map::ChildNodes::OnDisk(read_slice::<Node>(

        )?),

    };

    Ok((dirstate_map, parents))

}

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<'on_disk>(

        &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)

        }

    }

    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)?;

        let base_name_start = self.base_name_start()?;

        Ok(HgPath::new(&full_path.as_bytes()[base_name_start..]))

    }

    pub(super) fn path<'on_disk>(

        &self,

        on_disk: &'on_disk [u8],

    ) -> Result<dirstate_map::NodeKey<'on_disk>, DirstateV2ParseError> {

        Ok(WithBasename::from_raw_parts(

            Cow::Borrowed(self.full_path(on_disk)?),

            self.base_name_start()?,

        ))

    }

    pub(super) fn has_copy_source<'on_disk>(&self) -> bool {

        self.copy_source.start.get() != 0

    }

    pub(super) fn copy_source<'on_disk>(

        &self,

        on_disk: &'on_disk [u8],

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

        Ok(if self.has_copy_source() {

            Some(read_hg_path(on_disk, self.copy_source)?)

        } else {

            None

        })

    }

    pub(super) fn node_data(

        &self,

    ) -> Result<dirstate_map::NodeData, DirstateV2ParseError> {

        let entry = |state| {

            dirstate_map::NodeData::Entry(self.entry_with_given_state(state))

        };

        match self.state {

            b'\0' => Ok(dirstate_map::NodeData::None),

            b'd' => Ok(dirstate_map::NodeData::CachedDirectory {

                mtime: *self.data.as_timestamp(),

            }),

            b'n' => Ok(entry(EntryState::Normal)),

            b'a' => Ok(entry(EntryState::Added)),

            b'r' => Ok(entry(EntryState::Removed)),

            b'm' => Ok(entry(EntryState::Merged)),

            _ => Err(DirstateV2ParseError),

        }

    }

    pub(super) fn cached_directory_mtime(&self) -> Option<&Timestamp> {

        if self.state == b'd' {

            Some(self.data.as_timestamp())

        } else {

            None

        }

    }

    pub(super) fn state(

        &self,

    ) -> Result<Option<EntryState>, DirstateV2ParseError> {

        match self.state {

            b'\0' | b'd' => Ok(None),

            b'n' => Ok(Some(EntryState::Normal)),

            b'a' => Ok(Some(EntryState::Added)),

            b'r' => Ok(Some(EntryState::Removed)),

            b'm' => Ok(Some(EntryState::Merged)),

            _ => Err(DirstateV2ParseError),

        }

    }

    fn entry_with_given_state(&self, state: EntryState) -> DirstateEntry {

        DirstateEntry {

            state,

            mode: self.data.mode.get(),

            mtime: self.data.mtime.get(),

            size: self.data.size.get(),

        }

    }

    pub(super) fn entry(

        &self,

    ) -> Result<Option<DirstateEntry>, DirstateV2ParseError> {

        Ok(self

            .state()?

            .map(|state| self.entry_with_given_state(state)))

    }

    pub(super) fn children<'on_disk>(

        &self,

        on_disk: &'on_disk [u8],

    ) -> Result<&'on_disk [Node], DirstateV2ParseError> {

        read_slice::<Node>(on_disk, self.children)

    }

    pub(super) fn to_in_memory_node<'on_disk>(

        &self,

        on_disk: &'on_disk [u8],

    ) -> Result<dirstate_map::Node<'on_disk>, DirstateV2ParseError> {

        Ok(dirstate_map::Node {

            children: dirstate_map::ChildNodes::OnDisk(

                self.children(on_disk)?,

            ),

            copy_source: self.copy_source(on_disk)?.map(Cow::Borrowed),

            data: self.node_data()?,

            tracked_descendants_count: self.tracked_descendants_count.get(),

        })

    }

}

impl Entry {

    fn from_timestamp(timestamp: Timestamp) -> Self {

        // Safety: both types implement the `ByteCast` trait, so we could

        // safely use `as_bytes` and `from_bytes` to do this conversion. Using

        // `transmute` instead makes the compiler check that the two types

        // have the same size, which eliminates the error case of

        // `from_bytes`.

        unsafe { std::mem::transmute::<Timestamp, Entry>(timestamp) }

    }

    fn as_timestamp(&self) -> &Timestamp {

        // Safety: same as above in `from_timestamp`

        unsafe { &*(self as *const Entry as *const Timestamp) }

    }

}

impl Timestamp {

    pub fn seconds(&self) -> i64 {

        self.seconds.get()

    }