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luminotes
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luminotes/controller/Html_differ.py

220 lines
7.5 KiB
Python

import re
from difflib import SequenceMatcher
from htmllib import HTMLParser
from formatter import AbstractFormatter, NullWriter
from xml.sax.saxutils import quoteattr
class Html_differ( HTMLParser ):
"""
Generates an HTML diff for two HTML strings. It assumed that the input HTML is already cleaned.
"""
def __init__( self ):
HTMLParser.__init__( self, AbstractFormatter( NullWriter() ) )
self.result = []
self.requires_no_close = [ 'img', 'br' ]
WORD_AND_WHITESPACE_PATTERN = re.compile( "\S*\s*" )
def handle_data( self, data ):
# this turns "foo bar baz" into [ "foo ", "bar ", "baz" ] and extends the result with it
self.result.extend( self.WORD_AND_WHITESPACE_PATTERN.findall( data ) )
def handle_charref( self, ref ):
self.result.append( '&#%s;' % ref )
def handle_entityref( self, ref ):
self.result.append( '&%s;' % ref )
def handle_comment( self, comment ):
pass # ignore comments
def handle_starttag( self, tag, method, attrs ):
self.result.append( self.get_starttag_text() )
def handle_endtag( self, tag, attrs ):
if tag not in self.requires_no_close:
self.result.append( "</%s>" % tag )
def unknown_starttag( self, tag, attr ):
self.handle_starttag( tag, None, attr )
def unknown_endtag( self, tag ):
self.handle_endtag( tag, None )
# used to replace, for instance, "<br/>" with "<br />"
INVALID_TAG_PATTERN = re.compile( "(\S)/>" )
INVALID_TAG_FIX = "\\1 />"
def convert_html_to_list( self, html ):
"""
Given an HTML string, produce a list of its constituent elements (tags and text).
@type html: unicode
@param html: HTML string to parse
@rtype: [ unicode, ... ]
@return: parsed list of HTML elements
"""
self.reset()
self.result = []
html = self.INVALID_TAG_PATTERN.sub( self.INVALID_TAG_FIX, html )
self.feed( html )
return [ x for x in self.result if x != "" ]
def diff( self, html_a, html_b ):
"""
Return a composite HTML diff of the given HTML input strings. The returned string contains the
entirety of the input strings, but with deleted/modified text from html_a wrapped in <del> tags,
and inserted/modified text from html_b wrapped in <ins> tags.
@type html_a: unicode
@param html_a: original HTML string
@type html_b: unicode
@param html-b: modified HTML string
@rtype: unicode
@return: composite HTML diff
"""
# parse the two html strings into lists
a = self.convert_html_to_list( html_a )
b = self.convert_html_to_list( html_b )
# prepare the two lists for diffing, and then diff 'em
( a, b ) = self.prepare_lists( a, b )
return self.diff_lists( a, b )
SINGLE_TAG_PATTERN = re.compile( "<(\w+).*/>" ) # e.g. '<br/>' or '<br />' or '<img src="foo" />'
START_TAG_PATTERN = re.compile( "<(\w+).*>" ) # e.g. '<i>' or '<a href="foo">'
END_TAG_PATTERN = re.compile( "</(\w+)>" ) # e.g. '</i>' or '</a>'
@staticmethod
def track_open_tags( item, open_tags ):
"""
Add or remove from the open_tags list based on whether the given item contains a start or end
tag. If item does not contain any tag, then open_tags remains unchanged.
@type item: unicode
@param item: chunk of HTML, containing either an HTML tag or just text
@type open_tags: [ unicode, ... ]
@param open_tags: list of open tags
"""
match = Html_differ.SINGLE_TAG_PATTERN.search( item )
if match: return
match = Html_differ.START_TAG_PATTERN.search( item )
if match:
open_tags.append( match.group( 1 ) )
return
match = Html_differ.END_TAG_PATTERN.search( item )
if not match: return
tag = match.group( 1 )
if match and tag in open_tags:
open_tags.remove( tag )
def prepare_lists( self, a, b ):
"""
Prepare the two lists for diffing by merging together adjacent elements that occur within
modified start and end HTML tags.
For instance, if:
a = [ 'foo ', 'bar ', 'baz ', 'quux' ]
b = [ 'foo ', '<i>', 'bar ', 'baz', '</i> ', 'quux' ]
then the returned lists are as follows:
a = [ 'foo ', 'bar baz ', 'quux' ]
b = [ 'foo ', '<i>bar baz</i> ', 'quux' ]
Merging these elements together ensures that they're diffed as a single unit. Failing to perform
this step would mean that when a phrase in list a becomes italicized in list b, then it wouldn't
show up as modified in the resulting diff.
@type a: [ unicode, ... ]
@type b: [ unicode, ... ]
@rtype: ( [ unicode, ... ], [ unicode, ... ] )
@return: tuple of resulting list a and list b
"""
matcher = SequenceMatcher( None, a, b )
result_a = []
result_b = []
open_tags = [] # modified start tags
open_del_items = [] # deleted items within modified start and end tags
open_ins_items = [] # inserted items within modified start and end tags
for ( change_type, i1, i2, j1, j2 ) in matcher.get_opcodes():
if change_type == "equal":
equal_items = b[ j1:j2 ]
if len( open_tags ) == 0:
result_a.extend( equal_items )
result_b.extend( equal_items )
else:
open_del_items.extend( equal_items )
open_ins_items.extend( equal_items )
continue
# go through the altered items looking for start and end tags
orig_len_open_tags = len( open_tags )
for i in range( i1, i2 ):
Html_differ.track_open_tags( a[ i ], open_tags )
for j in range( j1, j2 ):
Html_differ.track_open_tags( b[ j ], open_tags )
all_tags_got_closed = ( orig_len_open_tags > 0 and len( open_tags ) == 0 )
if change_type == "replace":
open_del_items.extend( a[ i1:i2 ] )
open_ins_items.extend( b[ j1:j2 ] )
elif change_type == "delete":
open_del_items.extend( a[ i1:i2 ] )
elif change_type == "insert":
open_ins_items.extend( b[ j1:j2 ] )
if all_tags_got_closed:
# if all tags were just closed, then merge the items that were in those tags
if len( open_del_items ) > 0:
result_a.append( ''.join( open_del_items ) )
if len( open_ins_items ) > 0:
result_b.append( ''.join( open_ins_items ) )
open_del_items = []
open_ins_items = []
elif len( open_tags ) == 0:
result_a.extend( open_del_items )
result_b.extend( open_ins_items )
open_del_items = []
open_ins_items = []
if len( open_del_items ):
result_a.extend( open_del_items )
if len( open_ins_items ):
result_b.extend( open_ins_items )
return ( result_a, result_b )
def diff_lists( self, a, b ):
"""
Diff two prepared lists and return the result as an HTML string.
@type a: [ unicode, ... ]
@type b: [ unicode, ... ]
@rtype: unicode
@return: composite HTML diff
"""
matcher = SequenceMatcher( None, a, b )
result = []
open_tags = []
# inspired by http://www.aaronsw.com/2002/diff/
for ( change_type, i1, i2, j1, j2 ) in matcher.get_opcodes():
if change_type == "replace":
result.append(
'<del class="diff modified">' + ''.join( a[ i1:i2 ] ) + '</del>' + \
'<ins class="diff modified">' + ''.join( b[ j1:j2 ] ) + '</ins>'
)
elif change_type == "delete":
result.append( '<del class="diff">' + ''.join( a[ i1:i2 ] ) + '</del>' )
elif change_type == "insert":
result.append( '<ins class="diff">' + ''.join( b[ j1:j2 ] ) + '</ins>' )
elif change_type == "equal":
result.append( ''.join( b[ j1:j2 ] ) )
return "".join( result )