# storageutil.py - Storage functionality agnostic of backend implementation.

#

# Copyright 2018 Gregory Szorc <gregory.szorc@gmail.com>

#

# 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 hashlib

import re

from ..node import (

    nullid,

)

_nullhash = hashlib.sha1(nullid)

def hashrevisionsha1(text, p1, p2):

    """Compute the SHA-1 for revision data and its parents.

    This hash combines both the current file contents and its history

    in a manner that makes it easy to distinguish nodes with the same

    content in the revision graph.

    """

    # As of now, if one of the parent node is null, p2 is null

    if p2 == nullid:

        # deep copy of a hash is faster than creating one

        s = _nullhash.copy()

        s.update(p1)

    else:

        # none of the parent nodes are nullid

        if p1 < p2:

            a = p1

            b = p2

        else:

            a = p2

            b = p1

        s = hashlib.sha1(a)

        s.update(b)

    s.update(text)

    return s.digest()

METADATA_RE = re.compile(b'\x01\n')

def parsemeta(text):

    """Parse metadata header from revision data.

    Returns a 2-tuple of (metadata, offset), where both can be None if there

    is no metadata.

    """

    # text can be buffer, so we can't use .startswith or .index

    if text[:2] != b'\x01\n':

        return None, None

    s = METADATA_RE.search(text, 2).start()

    mtext = text[2:s]

    meta = {}

    for l in mtext.splitlines():

        k, v = l.split(b': ', 1)

        meta[k] = v

    return meta, s + 2

def packmeta(meta, text):

    """Add metadata to fulltext to produce revision text."""

    keys = sorted(meta)

    metatext = b''.join(b'%s: %s\n' % (k, meta[k]) for k in keys)

    return b'\x01\n%s\x01\n%s' % (metatext, text)

def iscensoredtext(text):

    meta = parsemeta(text)[0]

    return meta and b'censored' in meta

def filtermetadata(text):

    """Extract just the revision data from source text.

    Returns ``text`` unless it has a metadata header, in which case we return

    a new buffer without hte metadata.

    """

    if not text.startswith(b'\x01\n'):

        return text

    offset = text.index(b'\x01\n', 2)

    return text[offset + 2:]