blockprocessors.py

"""
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.

"""

import re
import markdown

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=None):
        self.parser = parser

    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(' '*markdown.TAB_LENGTH):
                newtext.append(line[markdown.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(' '*markdown.TAB_LENGTH*level):
                lines[i] = lines[i][markdown.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

    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


class ListIndentProcessor(BlockProcessor):
    """ Process children of list items. 
    
    Example:
        * a list item
            process this part

            or this part

    """

    INDENT_RE = re.compile(r'^(([ ]{%s})+)'% markdown.TAB_LENGTH)
    ITEM_TYPES = ['li']
    LIST_TYPES = ['ul', 'ol']

    def test(self, parent, block):
        return block.startswith(' '*markdown.TAB_LENGTH) and \
                not self.parser.state.isstate('detabbed') and  \
                (parent.tag in self.ITEM_TYPES or \
                    (len(parent) and parent[-1] 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:
            # 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
                block = '%s\n\n%s' % (sibling[-1].text, block)
                sibling[-1].text = ''
            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 = markdown.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))/markdown.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 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(' '*markdown.TAB_LENGTH)
    
    def run(self, parent, blocks):
        sibling = self.lastChild(parent)
        block = blocks.pop(0)
        theRest = ''
        if sibling 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 = markdown.AtomicString('%s\n%s\n' % (code.text, block.rstrip()))
        else:
            # This is a new codeblock. Create the elements and insert text.
            pre = markdown.etree.SubElement(parent, 'pre')
            code = markdown.etree.SubElement(pre, 'code')
            block, theRest = self.detab(block)
            code.text = markdown.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 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 = markdown.etree.SubElement(parent, 'blockquote')
        # Recursively parse block with blockquote as parent.
        self.parser.parseChunk(quote, block)

    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+\.)|[*+-])[ ]+.*')

    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 and sibling.tag in ['ol', 'ul']:
            # Previous block was a list item, so set that as parent
            lst = sibling
            # make sure previous item is in a p.
            if len(lst) and lst[-1].text and not len(lst[-1]):
                p = markdown.etree.SubElement(lst[-1], 'p')
                p.text = lst[-1].text
                lst[-1].text = ''
            # parse first block differently as it gets wrapped in a p.
            li = markdown.etree.SubElement(lst, 'li')
            self.parser.state.set('looselist')
            firstitem = items.pop(0)
            self.parser.parseBlocks(li, [firstitem])
            self.parser.state.reset()
        else:
            # This is a new list so create parent with appropriate tag.
            lst = markdown.etree.SubElement(parent, self.TAG)
        self.parser.state.set('list')
        # Loop through items in block, recursively parsing each with the
        # appropriate parent.
        for item in items:
            if item.startswith(' '*markdown.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 = markdown.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 item. Append
                items.append(m.group(3))
            elif self.INDENT_RE.match(line):
                # This is an indented (possibly nested) item.
                if items[-1].startswith(' '*markdown.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 = markdown.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:
            # This should never happen, but just in case...
            message(CRITICAL, "We've got a problem header!")


class SetextHeaderProcessor(BlockProcessor):
    """ Process Setext-style Headers. """

    # Detect Setext-style header. Must be first 2 lines of block.
    RE = re.compile(r'^.*?\n[=-]{3,}', 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 = markdown.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}(?P<ch>[*_-])[ ]?((?P=ch)[ ]?){2,}[ ]*'
    # Detect hr on any line of a block.
    SEARCH_RE = re.compile(r'(^|\n)%s(\n|$)' % RE)
    # Match a hr on a single line of text.
    MATCH_RE = re.compile(r'^%s$' % RE)

    def test(self, parent, block):
        return bool(self.SEARCH_RE.search(block))

    def run(self, parent, blocks):
        lines = blocks.pop(0).split('\n')
        prelines = []
        # Check for lines in block before hr.
        for line in lines:
            m = self.MATCH_RE.match(line)
            if m:
                break
            else:
                prelines.append(line)
        if len(prelines):
            # Recursively parse lines before hr so they get parsed first.
            self.parser.parseBlocks(parent, ['\n'.join(prelines)])
        # create hr
        hr = markdown.etree.SubElement(parent, 'hr')
        # check for lines in block after hr.
        lines = lines[len(prelines)+1:]
        if len(lines):
            # Add lines after hr to master blocks for later parsing.
            blocks.insert(0, '\n'.join(lines))


class EmptyBlockProcessor(BlockProcessor):
    """ Process blocks and start with an empty line. """

    # Detect a block that only contains whitespace 
    # or only whitespace on the first line.
    RE = re.compile(r'^\s*\n')

    def test(self, parent, block):
        return bool(self.RE.match(block))

    def run(self, parent, blocks):
        block = blocks.pop(0)
        m = self.RE.match(block)
        if m:
            # Add remaining line to master blocks for later.
            blocks.insert(0, block[m.end():])
            sibling = self.lastChild(parent)
            if sibling and sibling.tag == 'pre' and sibling[0] and \
                    sibling[0].tag == 'code':
                # Last block is a codeblock. Append to preserve whitespace.
                sibling[0].text = markdown.AtomicString('%s/n/n/n' % sibling[0].text )


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. 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 = markdown.etree.SubElement(parent, 'p')
                p.text = block.lstrip()