# nodemap.py - nodemap related code and utilities

#

# Copyright 2019 Pierre-Yves David <pierre-yves.david@octobus.net>

# Copyright 2019 George Racinet <georges.racinet@octobus.net>

#

# 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 .. import (

    error,

    node as nodemod,

    pycompat,

)

class NodeMap(dict):

    def __missing__(self, x):

        raise error.RevlogError(b'unknown node: %s' % x)

def setup_persistent_nodemap(tr, revlog):

    """Install whatever is needed transaction side to persist a nodemap on disk

    (only actually persist the nodemap if this is relevant for this revlog)

    """

    if revlog.nodemap_file is None:

        return  # we do not use persistent_nodemap on this revlog

    callback_id = b"revlog-persistent-nodemap-%s" % revlog.nodemap_file

    if tr.hasfinalize(callback_id):

        return  # no need to register again

    tr.addfinalize(callback_id, lambda tr: _persist_nodemap(tr, revlog))

def _persist_nodemap(tr, revlog):

    """Write nodemap data on disk for a given revlog

    """

    if getattr(revlog, 'filteredrevs', ()):

        raise error.ProgrammingError(

            "cannot persist nodemap of a filtered changelog"

        )

    if revlog.nodemap_file is None:

        msg = "calling persist nodemap on a revlog without the feature enableb"

        raise error.ProgrammingError(msg)

    data = persistent_data(revlog.index)

    # EXP-TODO: if this is a cache, this should use a cache vfs, not a

    # store vfs

    with revlog.opener(revlog.nodemap_file, b'w') as f:

        f.write(data)

    # EXP-TODO: if the transaction abort, we should remove the new data and

    # reinstall the old one. (This will be simpler when the file format get a

    # bit more advanced)

### Nodemap Trie

#

# This is a simple reference implementation to compute and persist a nodemap

# trie. This reference implementation is write only. The python version of this

# is not expected to be actually used, since it wont provide performance

# improvement over existing non-persistent C implementation.

#

# The nodemap is persisted as Trie using 4bits-address/16-entries block. each

# revision can be adressed using its node shortest prefix.

#

# The trie is stored as a sequence of block. Each block contains 16 entries

# (signed 64bit integer, big endian). Each entry can be one of the following:

#

#  * value >=  0 -> index of sub-block

#  * value == -1 -> no value

#  * value <  -1 -> a revision value: rev = -(value+10)

#

# The implementation focus on simplicity, not on performance. A Rust

# implementation should provide a efficient version of the same binary

# persistence. This reference python implementation is never meant to be

# extensively use in production.

def persistent_data(index):

    """return the persistent binary form for a nodemap for a given index

    """

    trie = _build_trie(index)

    return _persist_trie(trie)

S_BLOCK = struct.Struct(">" + ("l" * 16))

NO_ENTRY = -1

# rev 0 need to be -2 because 0 is used by block, -1 is a special value.

REV_OFFSET = 2

def _transform_rev(rev):

    """Return the number used to represent the rev in the tree.

    (or retrieve a rev number from such representation)

    Note that this is an involution, a function equal to its inverse (i.e.

    which gives the identity when applied to itself).

    """

    return -(rev + REV_OFFSET)

def _to_int(hex_digit):

    """turn an hexadecimal digit into a proper integer"""

    return int(hex_digit, 16)

def _build_trie(index):

    """build a nodemap trie

    The nodemap stores revision number for each unique prefix.

    Each block is a dictionary with keys in `[0, 15]`. Values are either

    another block or a revision number.

    """

    root = {}

    for rev in range(len(index)):

        hex = nodemod.hex(index[rev][7])

        _insert_into_block(index, 0, root, rev, hex)

    return root

def _insert_into_block(index, level, block, current_rev, current_hex):

    """insert a new revision in a block

    index: the index we are adding revision for

    level: the depth of the current block in the trie

    block: the block currently being considered

    current_rev: the revision number we are adding

    current_hex: the hexadecimal representation of the of that revision

    """

    hex_digit = _to_int(current_hex[level : level + 1])

    entry = block.get(hex_digit)

    if entry is None:

        # no entry, simply store the revision number

        block[hex_digit] = current_rev

    elif isinstance(entry, dict):

        # need to recurse to an underlying block

        _insert_into_block(index, level + 1, entry, current_rev, current_hex)

    else:

        # collision with a previously unique prefix, inserting new

        # vertices to fit both entry.

        other_hex = nodemod.hex(index[entry][7])

        other_rev = entry

        new = {}

        block[hex_digit] = new

        _insert_into_block(index, level + 1, new, other_rev, other_hex)

        _insert_into_block(index, level + 1, new, current_rev, current_hex)

def _persist_trie(root):

    """turn a nodemap trie into persistent binary data

    See `_build_trie` for nodemap trie structure"""

    block_map = {}

    chunks = []

    for tn in _walk_trie(root):

        block_map[id(tn)] = len(chunks)

        chunks.append(_persist_block(tn, block_map))

    return b''.join(chunks)

def _walk_trie(block):

    """yield all the block in a trie

    Children blocks are always yield before their parent block.

    """

    for (_, item) in sorted(block.items()):

        if isinstance(item, dict):

            for sub_block in _walk_trie(item):

                yield sub_block

    yield block

def _persist_block(block_node, block_map):

    """produce persistent binary data for a single block

    Children block are assumed to be already persisted and present in

    block_map.

    """

    data = tuple(_to_value(block_node.get(i), block_map) for i in range(16))

    return S_BLOCK.pack(*data)

def _to_value(item, block_map):

    """persist any value as an integer"""

    if item is None:

        return NO_ENTRY

    elif isinstance(item, dict):

        return block_map[id(item)]

    else:

        return _transform_rev(item)