Re-land "Check in a simple pure-python based Markdown previewer."

third_party/Python-Markdown/markdown/blockprocessors.py

Index: third_party/Python-Markdown/markdown/blockprocessors.py
diff --git a/third_party/Python-Markdown/markdown/blockprocessors.py b/third_party/Python-Markdown/markdown/blockprocessors.py
new file mode 100644
index 0000000000000000000000000000000000000000..29db022cee111b062818853bebaf99d6ffa1dcba
--- /dev/null
+++ b/third_party/Python-Markdown/markdown/blockprocessors.py
@@ -0,0 +1,563 @@
+"""
+CORE MARKDOWN BLOCKPARSER
+===========================================================================
+
+This parser handles basic parsing of Markdown blocks.  It doesn't concern
+itself with inline elements such as **bold** or *italics*, but rather just
+catches blocks, lists, quotes, etc.
+
+The BlockParser is made up of a bunch of BlockProssors, each handling a
+different type of block. Extensions may add/replace/remove BlockProcessors
+as they need to alter how markdown blocks are parsed.
+"""
+
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import unicode_literals
+import logging
+import re
+from . import util
+from .blockparser import BlockParser
+
+logger = logging.getLogger('MARKDOWN')
+
+
+def build_block_parser(md_instance, **kwargs):
+    """ Build the default block parser used by Markdown. """
+    parser = BlockParser(md_instance)
+    parser.blockprocessors['empty'] = EmptyBlockProcessor(parser)
+    parser.blockprocessors['indent'] = ListIndentProcessor(parser)
+    parser.blockprocessors['code'] = CodeBlockProcessor(parser)
+    parser.blockprocessors['hashheader'] = HashHeaderProcessor(parser)
+    parser.blockprocessors['setextheader'] = SetextHeaderProcessor(parser)
+    parser.blockprocessors['hr'] = HRProcessor(parser)
+    parser.blockprocessors['olist'] = OListProcessor(parser)
+    parser.blockprocessors['ulist'] = UListProcessor(parser)
+    parser.blockprocessors['quote'] = BlockQuoteProcessor(parser)
+    parser.blockprocessors['paragraph'] = ParagraphProcessor(parser)
+    return parser
+
+
+class BlockProcessor:
+    """ Base class for block processors.
+
+    Each subclass will provide the methods below to work with the source and
+    tree. Each processor will need to define it's own ``test`` and ``run``
+    methods. The ``test`` method should return True or False, to indicate
+    whether the current block should be processed by this processor. If the
+    test passes, the parser will call the processors ``run`` method.
+
+    """
+
+    def __init__(self, parser):
+        self.parser = parser
+        self.tab_length = parser.markdown.tab_length
+
+    def lastChild(self, parent):
+        """ Return the last child of an etree element. """
+        if len(parent):
+            return parent[-1]
+        else:
+            return None
+
+    def detab(self, text):
+        """ Remove a tab from the front of each line of the given text. """
+        newtext = []
+        lines = text.split('\n')
+        for line in lines:
+            if line.startswith(' '*self.tab_length):
+                newtext.append(line[self.tab_length:])
+            elif not line.strip():
+                newtext.append('')
+            else:
+                break
+        return '\n'.join(newtext), '\n'.join(lines[len(newtext):])
+
+    def looseDetab(self, text, level=1):
+        """ Remove a tab from front of lines but allowing dedented lines. """
+        lines = text.split('\n')
+        for i in range(len(lines)):
+            if lines[i].startswith(' '*self.tab_length*level):
+                lines[i] = lines[i][self.tab_length*level:]
+        return '\n'.join(lines)
+
+    def test(self, parent, block):
+        """ Test for block type. Must be overridden by subclasses.
+
+        As the parser loops through processors, it will call the ``test``
+        method on each to determine if the given block of text is of that
+        type. This method must return a boolean ``True`` or ``False``. The
+        actual method of testing is left to the needs of that particular
+        block type. It could be as simple as ``block.startswith(some_string)``
+        or a complex regular expression. As the block type may be different
+        depending on the parent of the block (i.e. inside a list), the parent
+        etree element is also provided and may be used as part of the test.
+
+        Keywords:
+
+        * ``parent``: A etree element which will be the parent of the block.
+        * ``block``: A block of text from the source which has been split at
+            blank lines.
+        """
+        pass  # pragma: no cover
+
+    def run(self, parent, blocks):
+        """ Run processor. Must be overridden by subclasses.
+
+        When the parser determines the appropriate type of a block, the parser
+        will call the corresponding processor's ``run`` method. This method
+        should parse the individual lines of the block and append them to
+        the etree.
+
+        Note that both the ``parent`` and ``etree`` keywords are pointers
+        to instances of the objects which should be edited in place. Each
+        processor must make changes to the existing objects as there is no
+        mechanism to return new/different objects to replace them.
+
+        This means that this method should be adding SubElements or adding text
+        to the parent, and should remove (``pop``) or add (``insert``) items to
+        the list of blocks.
+
+        Keywords:
+
+        * ``parent``: A etree element which is the parent of the current block.
+        * ``blocks``: A list of all remaining blocks of the document.
+        """
+        pass  # pragma: no cover
+
+
+class ListIndentProcessor(BlockProcessor):
+    """ Process children of list items.
+
+    Example:
+        * a list item
+            process this part
+
+            or this part
+
+    """
+
+    ITEM_TYPES = ['li']
+    LIST_TYPES = ['ul', 'ol']
+
+    def __init__(self, *args):
+        BlockProcessor.__init__(self, *args)
+        self.INDENT_RE = re.compile(r'^(([ ]{%s})+)' % self.tab_length)
+
+    def test(self, parent, block):
+        return block.startswith(' '*self.tab_length) and \
+            not self.parser.state.isstate('detabbed') and \
+            (parent.tag in self.ITEM_TYPES or
+                (len(parent) and parent[-1] is not None and
+                    (parent[-1].tag in self.LIST_TYPES)))
+
+    def run(self, parent, blocks):
+        block = blocks.pop(0)
+        level, sibling = self.get_level(parent, block)
+        block = self.looseDetab(block, level)
+
+        self.parser.state.set('detabbed')
+        if parent.tag in self.ITEM_TYPES:
+            # It's possible that this parent has a 'ul' or 'ol' child list
+            # with a member.  If that is the case, then that should be the
+            # parent.  This is intended to catch the edge case of an indented
+            # list whose first member was parsed previous to this point
+            # see OListProcessor
+            if len(parent) and parent[-1].tag in self.LIST_TYPES:
+                self.parser.parseBlocks(parent[-1], [block])
+            else:
+                # The parent is already a li. Just parse the child block.
+                self.parser.parseBlocks(parent, [block])
+        elif sibling.tag in self.ITEM_TYPES:
+            # The sibling is a li. Use it as parent.
+            self.parser.parseBlocks(sibling, [block])
+        elif len(sibling) and sibling[-1].tag in self.ITEM_TYPES:
+            # The parent is a list (``ol`` or ``ul``) which has children.
+            # Assume the last child li is the parent of this block.
+            if sibling[-1].text:
+                # If the parent li has text, that text needs to be moved to a p
+                # The p must be 'inserted' at beginning of list in the event
+                # that other children already exist i.e.; a nested sublist.
+                p = util.etree.Element('p')
+                p.text = sibling[-1].text
+                sibling[-1].text = ''
+                sibling[-1].insert(0, p)
+            self.parser.parseChunk(sibling[-1], block)
+        else:
+            self.create_item(sibling, block)
+        self.parser.state.reset()
+
+    def create_item(self, parent, block):
+        """ Create a new li and parse the block with it as the parent. """
+        li = util.etree.SubElement(parent, 'li')
+        self.parser.parseBlocks(li, [block])
+
+    def get_level(self, parent, block):
+        """ Get level of indent based on list level. """
+        # Get indent level
+        m = self.INDENT_RE.match(block)
+        if m:
+            indent_level = len(m.group(1))/self.tab_length
+        else:
+            indent_level = 0
+        if self.parser.state.isstate('list'):
+            # We're in a tightlist - so we already are at correct parent.
+            level = 1
+        else:
+            # We're in a looselist - so we need to find parent.
+            level = 0
+        # Step through children of tree to find matching indent level.
+        while indent_level > level:
+            child = self.lastChild(parent)
+            if (child is not None and
+               (child.tag in self.LIST_TYPES or child.tag in self.ITEM_TYPES)):
+                if child.tag in self.LIST_TYPES:
+                    level += 1
+                parent = child
+            else:
+                # No more child levels. If we're short of indent_level,
+                # we have a code block. So we stop here.
+                break
+        return level, parent
+
+
+class CodeBlockProcessor(BlockProcessor):
+    """ Process code blocks. """
+
+    def test(self, parent, block):
+        return block.startswith(' '*self.tab_length)
+
+    def run(self, parent, blocks):
+        sibling = self.lastChild(parent)
+        block = blocks.pop(0)
+        theRest = ''
+        if (sibling is not None and sibling.tag == "pre" and
+           len(sibling) and sibling[0].tag == "code"):
+            # The previous block was a code block. As blank lines do not start
+            # new code blocks, append this block to the previous, adding back
+            # linebreaks removed from the split into a list.
+            code = sibling[0]
+            block, theRest = self.detab(block)
+            code.text = util.AtomicString(
+                '%s\n%s\n' % (code.text, block.rstrip())
+            )
+        else:
+            # This is a new codeblock. Create the elements and insert text.
+            pre = util.etree.SubElement(parent, 'pre')
+            code = util.etree.SubElement(pre, 'code')
+            block, theRest = self.detab(block)
+            code.text = util.AtomicString('%s\n' % block.rstrip())
+        if theRest:
+            # This block contained unindented line(s) after the first indented
+            # line. Insert these lines as the first block of the master blocks
+            # list for future processing.
+            blocks.insert(0, theRest)
+
+
+class BlockQuoteProcessor(BlockProcessor):
+
+    RE = re.compile(r'(^|\n)[ ]{0,3}>[ ]?(.*)')
+
+    def test(self, parent, block):
+        return bool(self.RE.search(block))
+
+    def run(self, parent, blocks):
+        block = blocks.pop(0)
+        m = self.RE.search(block)
+        if m:
+            before = block[:m.start()]  # Lines before blockquote
+            # Pass lines before blockquote in recursively for parsing forst.
+            self.parser.parseBlocks(parent, [before])
+            # Remove ``> `` from begining of each line.
+            block = '\n'.join(
+                [self.clean(line) for line in block[m.start():].split('\n')]
+            )
+        sibling = self.lastChild(parent)
+        if sibling is not None and sibling.tag == "blockquote":
+            # Previous block was a blockquote so set that as this blocks parent
+            quote = sibling
+        else:
+            # This is a new blockquote. Create a new parent element.
+            quote = util.etree.SubElement(parent, 'blockquote')
+        # Recursively parse block with blockquote as parent.
+        # change parser state so blockquotes embedded in lists use p tags
+        self.parser.state.set('blockquote')
+        self.parser.parseChunk(quote, block)
+        self.parser.state.reset()
+
+    def clean(self, line):
+        """ Remove ``>`` from beginning of a line. """
+        m = self.RE.match(line)
+        if line.strip() == ">":
+            return ""
+        elif m:
+            return m.group(2)
+        else:
+            return line
+
+
+class OListProcessor(BlockProcessor):
+    """ Process ordered list blocks. """
+
+    TAG = 'ol'
+    # Detect an item (``1. item``). ``group(1)`` contains contents of item.
+    RE = re.compile(r'^[ ]{0,3}\d+\.[ ]+(.*)')
+    # Detect items on secondary lines. they can be of either list type.
+    CHILD_RE = re.compile(r'^[ ]{0,3}((\d+\.)|[*+-])[ ]+(.*)')
+    # Detect indented (nested) items of either type
+    INDENT_RE = re.compile(r'^[ ]{4,7}((\d+\.)|[*+-])[ ]+.*')
+    # The integer (python string) with which the lists starts (default=1)
+    # Eg: If list is intialized as)
+    #   3. Item
+    # The ol tag will get starts="3" attribute
+    STARTSWITH = '1'
+    # List of allowed sibling tags.
+    SIBLING_TAGS = ['ol', 'ul']
+
+    def test(self, parent, block):
+        return bool(self.RE.match(block))
+
+    def run(self, parent, blocks):
+        # Check fr multiple items in one block.
+        items = self.get_items(blocks.pop(0))
+        sibling = self.lastChild(parent)
+
+        if sibling is not None and sibling.tag in self.SIBLING_TAGS:
+            # Previous block was a list item, so set that as parent
+            lst = sibling
+            # make sure previous item is in a p- if the item has text,
+            # then it isn't in a p
+            if lst[-1].text:
+                # since it's possible there are other children for this
+                # sibling, we can't just SubElement the p, we need to
+                # insert it as the first item.
+                p = util.etree.Element('p')
+                p.text = lst[-1].text
+                lst[-1].text = ''
+                lst[-1].insert(0, p)
+            # if the last item has a tail, then the tail needs to be put in a p
+            # likely only when a header is not followed by a blank line
+            lch = self.lastChild(lst[-1])
+            if lch is not None and lch.tail:
+                p = util.etree.SubElement(lst[-1], 'p')
+                p.text = lch.tail.lstrip()
+                lch.tail = ''
+
+            # parse first block differently as it gets wrapped in a p.
+            li = util.etree.SubElement(lst, 'li')
+            self.parser.state.set('looselist')
+            firstitem = items.pop(0)
+            self.parser.parseBlocks(li, [firstitem])
+            self.parser.state.reset()
+        elif parent.tag in ['ol', 'ul']:
+            # this catches the edge case of a multi-item indented list whose
+            # first item is in a blank parent-list item:
+            # * * subitem1
+            #     * subitem2
+            # see also ListIndentProcessor
+            lst = parent
+        else:
+            # This is a new list so create parent with appropriate tag.
+            lst = util.etree.SubElement(parent, self.TAG)
+            # Check if a custom start integer is set
+            if not self.parser.markdown.lazy_ol and self.STARTSWITH != '1':
+                lst.attrib['start'] = self.STARTSWITH
+
+        self.parser.state.set('list')
+        # Loop through items in block, recursively parsing each with the
+        # appropriate parent.
+        for item in items:
+            if item.startswith(' '*self.tab_length):
+                # Item is indented. Parse with last item as parent
+                self.parser.parseBlocks(lst[-1], [item])
+            else:
+                # New item. Create li and parse with it as parent
+                li = util.etree.SubElement(lst, 'li')
+                self.parser.parseBlocks(li, [item])
+        self.parser.state.reset()
+
+    def get_items(self, block):
+        """ Break a block into list items. """
+        items = []
+        for line in block.split('\n'):
+            m = self.CHILD_RE.match(line)
+            if m:
+                # This is a new list item
+                # Check first item for the start index
+                if not items and self.TAG == 'ol':
+                    # Detect the integer value of first list item
+                    INTEGER_RE = re.compile('(\d+)')
+                    self.STARTSWITH = INTEGER_RE.match(m.group(1)).group()
+                # Append to the list
+                items.append(m.group(3))
+            elif self.INDENT_RE.match(line):
+                # This is an indented (possibly nested) item.
+                if items[-1].startswith(' '*self.tab_length):
+                    # Previous item was indented. Append to that item.
+                    items[-1] = '%s\n%s' % (items[-1], line)
+                else:
+                    items.append(line)
+            else:
+                # This is another line of previous item. Append to that item.
+                items[-1] = '%s\n%s' % (items[-1], line)
+        return items
+
+
+class UListProcessor(OListProcessor):
+    """ Process unordered list blocks. """
+
+    TAG = 'ul'
+    RE = re.compile(r'^[ ]{0,3}[*+-][ ]+(.*)')
+
+
+class HashHeaderProcessor(BlockProcessor):
+    """ Process Hash Headers. """
+
+    # Detect a header at start of any line in block
+    RE = re.compile(r'(^|\n)(?P<level>#{1,6})(?P<header>.*?)#*(\n|$)')
+
+    def test(self, parent, block):
+        return bool(self.RE.search(block))
+
+    def run(self, parent, blocks):
+        block = blocks.pop(0)
+        m = self.RE.search(block)
+        if m:
+            before = block[:m.start()]  # All lines before header
+            after = block[m.end():]     # All lines after header
+            if before:
+                # As the header was not the first line of the block and the
+                # lines before the header must be parsed first,
+                # recursively parse this lines as a block.
+                self.parser.parseBlocks(parent, [before])
+            # Create header using named groups from RE
+            h = util.etree.SubElement(parent, 'h%d' % len(m.group('level')))
+            h.text = m.group('header').strip()
+            if after:
+                # Insert remaining lines as first block for future parsing.
+                blocks.insert(0, after)
+        else:  # pragma: no cover
+            # This should never happen, but just in case...
+            logger.warn("We've got a problem header: %r" % block)
+
+
+class SetextHeaderProcessor(BlockProcessor):
+    """ Process Setext-style Headers. """
+
+    # Detect Setext-style header. Must be first 2 lines of block.
+    RE = re.compile(r'^.*?\n[=-]+[ ]*(\n|$)', re.MULTILINE)
+
+    def test(self, parent, block):
+        return bool(self.RE.match(block))
+
+    def run(self, parent, blocks):
+        lines = blocks.pop(0).split('\n')
+        # Determine level. ``=`` is 1 and ``-`` is 2.
+        if lines[1].startswith('='):
+            level = 1
+        else:
+            level = 2
+        h = util.etree.SubElement(parent, 'h%d' % level)
+        h.text = lines[0].strip()
+        if len(lines) > 2:
+            # Block contains additional lines. Add to  master blocks for later.
+            blocks.insert(0, '\n'.join(lines[2:]))
+
+
+class HRProcessor(BlockProcessor):
+    """ Process Horizontal Rules. """
+
+    RE = r'^[ ]{0,3}((-+[ ]{0,2}){3,}|(_+[ ]{0,2}){3,}|(\*+[ ]{0,2}){3,})[ ]*'
+    # Detect hr on any line of a block.
+    SEARCH_RE = re.compile(RE, re.MULTILINE)
+
+    def test(self, parent, block):
+        m = self.SEARCH_RE.search(block)
+        # No atomic grouping in python so we simulate it here for performance.
+        # The regex only matches what would be in the atomic group - the HR.
+        # Then check if we are at end of block or if next char is a newline.
+        if m and (m.end() == len(block) or block[m.end()] == '\n'):
+            # Save match object on class instance so we can use it later.
+            self.match = m
+            return True
+        return False
+
+    def run(self, parent, blocks):
+        block = blocks.pop(0)
+        # Check for lines in block before hr.
+        prelines = block[:self.match.start()].rstrip('\n')
+        if prelines:
+            # Recursively parse lines before hr so they get parsed first.
+            self.parser.parseBlocks(parent, [prelines])
+        # create hr
+        util.etree.SubElement(parent, 'hr')
+        # check for lines in block after hr.
+        postlines = block[self.match.end():].lstrip('\n')
+        if postlines:
+            # Add lines after hr to master blocks for later parsing.
+            blocks.insert(0, postlines)
+
+
+class EmptyBlockProcessor(BlockProcessor):
+    """ Process blocks that are empty or start with an empty line. """
+
+    def test(self, parent, block):
+        return not block or block.startswith('\n')
+
+    def run(self, parent, blocks):
+        block = blocks.pop(0)
+        filler = '\n\n'
+        if block:
+            # Starts with empty line
+            # Only replace a single line.
+            filler = '\n'
+            # Save the rest for later.
+            theRest = block[1:]
+            if theRest:
+                # Add remaining lines to master blocks for later.
+                blocks.insert(0, theRest)
+        sibling = self.lastChild(parent)
+        if (sibling is not None and sibling.tag == 'pre' and
+           len(sibling) and sibling[0].tag == 'code'):
+            # Last block is a codeblock. Append to preserve whitespace.
+            sibling[0].text = util.AtomicString(
+                '%s%s' % (sibling[0].text, filler)
+            )
+
+
+class ParagraphProcessor(BlockProcessor):
+    """ Process Paragraph blocks. """
+
+    def test(self, parent, block):
+        return True
+
+    def run(self, parent, blocks):
+        block = blocks.pop(0)
+        if block.strip():
+            # Not a blank block. Add to parent, otherwise throw it away.
+            if self.parser.state.isstate('list'):
+                # The parent is a tight-list.
+                #
+                # Check for any children. This will likely only happen in a
+                # tight-list when a header isn't followed by a blank line.
+                # For example:
+                #
+                #     * # Header
+                #     Line 2 of list item - not part of header.
+                sibling = self.lastChild(parent)
+                if sibling is not None:
+                    # Insetrt after sibling.
+                    if sibling.tail:
+                        sibling.tail = '%s\n%s' % (sibling.tail, block)
+                    else:
+                        sibling.tail = '\n%s' % block
+                else:
+                    # Append to parent.text
+                    if parent.text:
+                        parent.text = '%s\n%s' % (parent.text, block)
+                    else:
+                        parent.text = block.lstrip()
+            else:
+                # Create a regular paragraph
+                p = util.etree.SubElement(parent, 'p')
+                p.text = block.lstrip()