# v2.py - Pure-Python implementation of the dirstate-v2 file format

#

# Copyright Mercurial Contributors

#

# This software may be used and distributed according to the terms of the

# GNU General Public License version 2 or any later version.

from __future__ import absolute_import

import struct

from ..thirdparty import attr

from .. import error, policy

parsers = policy.importmod('parsers')

# Must match the constant of the same name in

# `rust/hg-core/src/dirstate_tree/on_disk.rs`

TREE_METADATA_SIZE = 44

NODE_SIZE = 44

# Must match the `TreeMetadata` Rust struct in

# `rust/hg-core/src/dirstate_tree/on_disk.rs`. See doc-comments there.

#

# * 4 bytes: start offset of root nodes

# * 4 bytes: number of root nodes

# * 4 bytes: total number of nodes in the tree that have an entry

# * 4 bytes: total number of nodes in the tree that have a copy source

# * 4 bytes: number of bytes in the data file that are not used anymore

# * 4 bytes: unused

# * 20 bytes: SHA-1 hash of ignore patterns

TREE_METADATA = struct.Struct('>LLLLL4s20s')

# Must match the `Node` Rust struct in

# `rust/hg-core/src/dirstate_tree/on_disk.rs`. See doc-comments there.

#

# * 4 bytes: start offset of full path

# * 2 bytes: length of the full path

# * 2 bytes: length within the full path before its "base name"

# * 4 bytes: start offset of the copy source if any, or zero for no copy source

# * 2 bytes: length of the copy source if any, or unused

# * 4 bytes: start offset of child nodes

# * 4 bytes: number of child nodes

# * 4 bytes: number of descendant nodes that have an entry

# * 4 bytes: number of descendant nodes that have a "tracked" state

# * 1 byte: flags

# * 4 bytes: expected size

# * 4 bytes: mtime seconds

# * 4 bytes: mtime nanoseconds

NODE = struct.Struct('>LHHLHLLLLHlll')

assert TREE_METADATA_SIZE == TREE_METADATA.size

assert NODE_SIZE == NODE.size

def parse_dirstate(map, copy_map, data, tree_metadata):

    """parse a full v2-dirstate from a binary data into dictionnaries:

    - map: a {path: entry} mapping that will be filled

    - copy_map: a {path: copy-source} mapping that will be filled

    - data: a binary blob contains v2 nodes data

    - tree_metadata:: a binary blob of the top level node (from the docket)

    """

    (

        root_nodes_start,

        root_nodes_len,

        _nodes_with_entry_count,

        _nodes_with_copy_source_count,

        _unreachable_bytes,

        _unused,

        _ignore_patterns_hash,

    ) = TREE_METADATA.unpack(tree_metadata)

    parse_nodes(map, copy_map, data, root_nodes_start, root_nodes_len)

def parse_nodes(map, copy_map, data, start, len):

    """parse <len> nodes from <data> starting at offset <start>

    This is used by parse_dirstate to recursively fill `map` and `copy_map`.

    All directory specific information is ignored and do not need any

    """

    for i in range(len):

        node_start = start + NODE_SIZE * i

        node_bytes = slice_with_len(data, node_start, NODE_SIZE)

        (

            path_start,

            path_len,

            _basename_start,

            copy_source_start,

            copy_source_len,

            children_start,

            children_count,

            _descendants_with_entry_count,

            _tracked_descendants_count,

            flags,

            size,

            mtime_s,

            mtime_ns,

        ) = NODE.unpack(node_bytes)

        # Parse child nodes of this node recursively

        parse_nodes(map, copy_map, data, children_start, children_count)

        item = parsers.DirstateItem.from_v2_data(flags, size, mtime_s, mtime_ns)

        if not item.any_tracked:

            continue

        path = slice_with_len(data, path_start, path_len)

        map[path] = item

        if copy_source_start:

            copy_map[path] = slice_with_len(

                data, copy_source_start, copy_source_len

            )

def slice_with_len(data, start, len):

    return data[start : start + len]

@attr.s

class Node(object):

    path = attr.ib()

    entry = attr.ib()

    parent = attr.ib(default=None)

    children_count = attr.ib(default=0)

    children_offset = attr.ib(default=0)

    descendants_with_entry = attr.ib(default=0)

    tracked_descendants = attr.ib(default=0)

    def pack(self, copy_map, paths_offset):

        path = self.path

        copy = copy_map.get(path)

        entry = self.entry

        path_start = paths_offset

        path_len = len(path)

        basename_start = path.rfind(b'/') + 1  # 0 if rfind returns -1

        if copy is not None:

            copy_source_start = paths_offset + len(path)

            copy_source_len = len(copy)

        else:

            copy_source_start = 0

            copy_source_len = 0

        if entry is not None:

            flags, size, mtime_s, mtime_ns = entry.v2_data()

        else:

            # There are no mtime-cached directories in the Python implementation

            size = 0

            mtime_s = 0

            mtime_ns = 0

        return NODE.pack(

            path_start,

            path_len,

            basename_start,

            copy_source_start,

            copy_source_len,

            self.children_offset,

            self.children_count,

            self.descendants_with_entry,

            self.tracked_descendants,

            flags,

            size,

            mtime_s,

            mtime_ns,

        )

def pack_dirstate(map, copy_map, now):

    """

    Pack `map` and `copy_map` into the dirstate v2 binary format and return

    the bytearray.

    `now` is a timestamp of the current filesystem time used to detect race

    conditions in writing the dirstate to disk, see inline comment.

    The on-disk format expects a tree-like structure where the leaves are

    written first (and sorted per-directory), going up levels until the root

    node and writing that one to the docket. See more details on the on-disk

    format in `mercurial/helptext/internals/dirstate-v2`.

    Since both `map` and `copy_map` are flat dicts we need to figure out the

    hierarchy. This algorithm does so without having to build the entire tree

    in-memory: it only keeps the minimum number of nodes around to satisfy the

    format.

    # Algorithm explanation

    This explanation does not talk about the different counters for tracked

    descendents and storing the copies, but that work is pretty simple once this

    algorithm is in place.

    ## Building a subtree

    First, sort `map`: this makes it so the leaves of the tree are contiguous

    per directory (i.e. a/b/c and a/b/d will be next to each other in the list),

    and enables us to use the ordering of folders to have a "cursor" of the

    current folder we're in without ever going twice in the same branch of the

    tree. The cursor is a node that remembers its parent and any information

    relevant to the format (see the `Node` class), building the relevant part

    of the tree lazily.

    Then, for each file in `map`, move the cursor into the tree to the

    corresponding folder of the file: for example, if the very first file

    is "a/b/c", we start from `Node[""]`, create `Node["a"]` which points to

    its parent `Node[""]`, then create `Node["a/b"]`, which points to its parent

    `Node["a"]`. These nodes are kept around in a stack.

    If the next file in `map` is in the same subtree ("a/b/d" or "a/b/e/f"), we

    add it to the stack and keep looping with the same logic of creating the

    tree nodes as needed. If however the next file in `map` is *not* in the same

    subtree ("a/other", if we're still in the "a/b" folder), then we know that

    the subtree we're in is complete.

    ## Writing the subtree

    We have the entire subtree in the stack, so we start writing it to disk

    folder by folder. The way we write a folder is to pop the stack into a list

    until the folder changes, revert this list of direct children (to satisfy

    the format requirement that children be sorted). This process repeats until

    we hit the "other" subtree.

    An example:

        a

        dir1/b

        dir1/c

        dir2/dir3/d

        dir2/dir3/e

        dir2/f

    Would have us:

        - add to the stack until "dir2/dir3/e"

        - realize that "dir2/f" is in a different subtree

        - pop "dir2/dir3/e", "dir2/dir3/d", reverse them so they're sorted and

          pack them since the next entry is "dir2/dir3"

        - go back up to "dir2"

        - add "dir2/f" to the stack

        - realize we're done with the map

        - pop "dir2/f", "dir2/dir3" from the stack, reverse and pack them

        - go up to the root node, do the same to write "a", "dir1" and "dir2" in

          that order

    ## Special case for the root node

    The root node is not serialized in the format, but its information is

    written to the docket. Again, see more details on the on-disk format in

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

    """

    data = bytearray()

    root_nodes_start = 0

    root_nodes_len = 0

    nodes_with_entry_count = 0

    nodes_with_copy_source_count = 0

    # Will always be 0 since this implementation always re-writes everything

    # to disk

    unreachable_bytes = 0

    unused = b'\x00' * 4

    # This is an optimization that's only useful for the Rust implementation

    ignore_patterns_hash = b'\x00' * 20

    if len(map) == 0:

        tree_metadata = TREE_METADATA.pack(

            root_nodes_start,

            root_nodes_len,

            nodes_with_entry_count,

            nodes_with_copy_source_count,

            unreachable_bytes,

            unused,

            ignore_patterns_hash,

        )

        return data, tree_metadata

    sorted_map = sorted(map.items(), key=lambda x: x[0])

    # Use a stack to not have to only remember the nodes we currently need

    # instead of building the entire tree in memory

    stack = []

    current_node = Node(b"", None)

    stack.append(current_node)

    for index, (path, entry) in enumerate(sorted_map, 1):

        if entry.need_delay(now):

            # The file was last modified "simultaneously" with the current

            # write to dirstate (i.e. within the same second for file-

            # systems with a granularity of 1 sec). This commonly happens

            # for at least a couple of files on 'update'.

            # The user could change the file without changing its size

            # within the same second. Invalidate the file's mtime in

            # dirstate, forcing future 'status' calls to compare the

            # contents of the file if the size is the same. This prevents

            # mistakenly treating such files as clean.

            entry.set_possibly_dirty()

        nodes_with_entry_count += 1

        if path in copy_map:

            nodes_with_copy_source_count += 1

        current_folder = get_folder(path)

        current_node = move_to_correct_node_in_tree(

            current_folder, current_node, stack

        )

        current_node.children_count += 1

        # Entries from `map` are never `None`

        if entry.tracked:

            current_node.tracked_descendants += 1

        current_node.descendants_with_entry += 1

        stack.append(Node(path, entry, current_node))

        should_pack = True

        next_path = None

        if index < len(sorted_map):

            # Determine if the next entry is in the same sub-tree, if so don't

            # pack yet

            next_path = sorted_map[index][0]

            should_pack = not get_folder(next_path).startswith(current_folder)

        if should_pack:

            pack_directory_children(current_node, copy_map, data, stack)

            while stack and current_node.path != b"":

                # Go up the tree and write until we reach the folder of the next

                # entry (if any, otherwise the root)

                parent = current_node.parent

                in_parent_folder_of_next_entry = next_path is not None and (

                    get_folder(next_path).startswith(get_folder(stack[-1].path))

                )

                if parent is None or in_parent_folder_of_next_entry:

                    break

                pack_directory_children(parent, copy_map, data, stack)

                current_node = parent

    # Special case for the root node since we don't write it to disk, only its

    # children to the docket

    current_node = stack.pop()

    assert current_node.path == b"", current_node.path

    assert len(stack) == 0, len(stack)

    tree_metadata = TREE_METADATA.pack(

        current_node.children_offset,

        current_node.children_count,

        nodes_with_entry_count,

        nodes_with_copy_source_count,

        unreachable_bytes,

        unused,

        ignore_patterns_hash,

    )

    return data, tree_metadata

def get_folder(path):

    """

    Return the folder of the path that's given, an empty string for root paths.

    """

    return path.rsplit(b'/', 1)[0] if b'/' in path else b''

def move_to_correct_node_in_tree(target_folder, current_node, stack):

    """

    Move inside the dirstate node tree to the node corresponding to

    `target_folder`, creating the missing nodes along the way if needed.

    """

    while target_folder != current_node.path:

        if target_folder.startswith(current_node.path):

            # We need to go down a folder

            prefix = target_folder[len(current_node.path) :].lstrip(b'/')

            subfolder_name = prefix.split(b'/', 1)[0]

            if current_node.path:

                subfolder_path = current_node.path + b'/' + subfolder_name

            else:

                subfolder_path = subfolder_name

            next_node = stack[-1]

            if next_node.path == target_folder:

                # This folder is now a file and only contains removed entries

                # merge with the last node

                current_node = next_node

            else:

                current_node.children_count += 1

                current_node = Node(subfolder_path, None, current_node)

                stack.append(current_node)

        else:

            # We need to go up a folder

            current_node = current_node.parent

    return current_node

def pack_directory_children(node, copy_map, data, stack):

    """

    Write the binary representation of the direct sorted children of `node` to

    `data`

    """

    direct_children = []

    while stack[-1].path != b"" and get_folder(stack[-1].path) == node.path:

        direct_children.append(stack.pop())

    if not direct_children:

        raise error.ProgrammingError(b"no direct children for %r" % node.path)

    # Reverse the stack to get the correct sorted order

    direct_children.reverse()

    packed_children = bytearray()

    # Write the paths to `data`. Pack child nodes but don't write them yet

    for child in direct_children:

        packed = child.pack(copy_map=copy_map, paths_offset=len(data))

        packed_children.extend(packed)

        data.extend(child.path)

        data.extend(copy_map.get(child.path, b""))

        node.tracked_descendants += child.tracked_descendants

        node.descendants_with_entry += child.descendants_with_entry

    # Write the fixed-size child nodes all together

    node.children_offset = len(data)

    data.extend(packed_children)