path: root/markdown/util.py

# -*- coding: utf-8 -*-
from __future__ import unicode_literals
import re
import sys
from collections import namedtuple


"""
Python 3 Stuff
=============================================================================
"""
PY3 = sys.version_info[0] == 3

if PY3:  # pragma: no cover
    string_type = str
    text_type = str
    int2str = chr
else:  # pragma: no cover
    string_type = basestring   # noqa
    text_type = unicode        # noqa
    int2str = unichr           # noqa


"""
Constants you might want to modify
-----------------------------------------------------------------------------
"""


BLOCK_LEVEL_ELEMENTS = re.compile(
    "^(p|div|h[1-6]|blockquote|pre|table|dl|ol|ul"
    "|script|noscript|form|fieldset|iframe|math"
    "|hr|hr/|style|li|dt|dd|thead|tbody"
    "|tr|th|td|section|footer|header|group|figure"
    "|figcaption|aside|article|canvas|output"
    "|progress|video|nav)$",
    re.IGNORECASE
)
# Placeholders
STX = '\u0002'  # Use STX ("Start of text") for start-of-placeholder
ETX = '\u0003'  # Use ETX ("End of text") for end-of-placeholder
INLINE_PLACEHOLDER_PREFIX = STX+"klzzwxh:"
INLINE_PLACEHOLDER = INLINE_PLACEHOLDER_PREFIX + "%s" + ETX
INLINE_PLACEHOLDER_RE = re.compile(INLINE_PLACEHOLDER % r'([0-9]+)')
AMP_SUBSTITUTE = STX+"amp"+ETX
HTML_PLACEHOLDER = STX + "wzxhzdk:%s" + ETX
HTML_PLACEHOLDER_RE = re.compile(HTML_PLACEHOLDER % r'([0-9]+)')
TAG_PLACEHOLDER = STX + "hzzhzkh:%s" + ETX


"""
Constants you probably do not need to change
-----------------------------------------------------------------------------
"""

RTL_BIDI_RANGES = (
    ('\u0590', '\u07FF'),
    # Hebrew (0590-05FF), Arabic (0600-06FF),
    # Syriac (0700-074F), Arabic supplement (0750-077F),
    # Thaana (0780-07BF), Nko (07C0-07FF).
    ('\u2D30', '\u2D7F')  # Tifinagh
)

# Extensions should use "markdown.util.etree" instead of "etree" (or do `from
# markdown.util import etree`).  Do not import it by yourself.

try:  # pragma: no cover
    # Is the C implementation of ElementTree available?
    import xml.etree.cElementTree as etree
    from xml.etree.ElementTree import Comment
    # Serializers (including ours) test with non-c Comment
    etree.test_comment = Comment
    if etree.VERSION < "1.0.5":
        raise RuntimeError("cElementTree version 1.0.5 or higher is required.")
except (ImportError, RuntimeError):  # pragma: no cover
    # Use the Python implementation of ElementTree?
    import xml.etree.ElementTree as etree
    if etree.VERSION < "1.1":
        raise RuntimeError("ElementTree version 1.1 or higher is required")


"""
AUXILIARY GLOBAL FUNCTIONS
=============================================================================
"""


def isBlockLevel(tag):
    """Check if the tag is a block level HTML tag."""
    if isinstance(tag, string_type):
        return BLOCK_LEVEL_ELEMENTS.match(tag)
    # Some ElementTree tags are not strings, so return False.
    return False


def parseBoolValue(value, fail_on_errors=True, preserve_none=False):
    """Parses a string representing bool value. If parsing was successful,
       returns True or False. If preserve_none=True, returns True, False,
       or None. If parsing was not successful, raises  ValueError, or, if
       fail_on_errors=False, returns None."""
    if not isinstance(value, string_type):
        if preserve_none and value is None:
            return value
        return bool(value)
    elif preserve_none and value.lower() == 'none':
        return None
    elif value.lower() in ('true', 'yes', 'y', 'on', '1'):
        return True
    elif value.lower() in ('false', 'no', 'n', 'off', '0', 'none'):
        return False
    elif fail_on_errors:
        raise ValueError('Cannot parse bool value: %r' % value)


"""
MISC AUXILIARY CLASSES
=============================================================================
"""


class AtomicString(text_type):
    """A string which should not be further processed."""
    pass


class Processor(object):
    def __init__(self, md=None):
        if md:
            self.md = md


class HtmlStash(object):
    """
    This class is used for stashing HTML objects that we extract
    in the beginning and replace with place-holders.
    """

    def __init__(self):
        """ Create a HtmlStash. """
        self.html_counter = 0  # for counting inline html segments
        self.rawHtmlBlocks = []
        self.tag_counter = 0
        self.tag_data = []  # list of dictionaries in the order tags appear

    def store(self, html):
        """
        Saves an HTML segment for later reinsertion.  Returns a
        placeholder string that needs to be inserted into the
        document.

        Keyword arguments:

        * html: an html segment

        Returns : a placeholder string

        """
        self.rawHtmlBlocks.append(html)
        placeholder = self.get_placeholder(self.html_counter)
        self.html_counter += 1
        return placeholder

    def reset(self):
        self.html_counter = 0
        self.rawHtmlBlocks = []

    def get_placeholder(self, key):
        return HTML_PLACEHOLDER % key

    def store_tag(self, tag, attrs, left_index, right_index):
        """Store tag data and return a placeholder."""
        self.tag_data.append({'tag': tag, 'attrs': attrs,
                              'left_index': left_index,
                              'right_index': right_index})
        placeholder = TAG_PLACEHOLDER % str(self.tag_counter)
        self.tag_counter += 1  # equal to the tag's index in self.tag_data
        return placeholder


# Used internally by `Registry` for each item in its sorted list.
# Provides an easier to read API when editing the code later.
# For example, `item.name` is more clear than `item[0]`.
_PriorityItem = namedtuple('PriorityItem', ['name', 'priority'])


class Registry(object):
    """
    A priority sorted registry.

    A `Registry` instance provides two public methods to alter the data of the
    registry: `register` and `deregister`. Use `register` to add items and
    `deregister` to remove items. See each method for specifics.

    When registering an item, a "name" and a "priority" must be provided. All
    items are automatically sorted by "priority" from highest to lowest. The
    "name" is used to remove ("deregister") and get items.

    A `Registry` instance it like a list (which maintains order) when reading
    data. You may iterate over the items, get an item and get a count (length)
    of all items. You may also check that the registry contains an item.

    When getting an item you may use either the index of the item or the
    string-based "name". For example:

        registry = Registry()
        registry.register(SomeItem(), 'itemname', 20)
        # Get the item by index
        item = registry[0]
        # Get the item by name
        item = registry['itemname']

    When checking that the registry contains an item, you may use either the
    string-based "name", or a reference to the actual item. For example:

        someitem = SomeItem()
        registry.register(someitem, 'itemname', 20)
        # Contains the name
        assert 'itemname' in registry
        # Contains the item instance
        assert someitem in registry

    The method `get_index_for_name` is also available to obtain the index of
    an item using that item's assigned "name".
    """

    def __init__(self):
        self._data = {}
        self._priority = []
        self._is_sorted = False

    def __contains__(self, item):
        if isinstance(item, string_type):
            # Check if an item exists by this name.
            return item in self._data.keys()
        # Check if this instance exists.
        return item in self._data.values()

    def __iter__(self):
        self._sort()
        return iter([self._data[k] for k, p in self._priority])

    def __getitem__(self, key):
        self._sort()
        if isinstance(key, slice):
            data = Registry()
            for k, p in self._priority[key]:
                data.register(self._data[k], k, p)
            return data
        if isinstance(key, int):
            return self._data[self._priority[key].name]
        return self._data[key]

    def __len__(self):
        return len(self._priority)

    def __repr__(self):
        return '<{0}({1})>'.format(self.__class__.__name__, list(self))

    def get_index_for_name(self, name):
        """
        Return the index of the given name.
        """
        self._sort()
        if name in self:
            return self._priority.index(
                [x for x in self._priority if x.name == name][0]
            )
        raise ValueError('No item named "{0}" exists.'.format(name))

    def register(self, item, name, priority):
        """
        Add an item to the registry with the given name and priority.

        Parameters:

        * `item`: The item being registered.
        * `name`: A string used to reference the item.
        * `priority`: An integer or float used to sort against all items.

        If an item is registered with a "name" which already exists, the
        existing item is replaced with the new item. Tread carefully as the
        old item is lost with no way to recover it. The new item will be
        sorted according to its priority and will **not** retain the position
        of the old item.
        """
        if name in self:
            # Remove existing item of same name first
            self.deregister(name)
        self._is_sorted = False
        self._data[name] = item
        self._priority.append(_PriorityItem(name, priority))

    def deregister(self, name, strict=True):
        """
        Remove an item from the registry.

        Set `strict=False` to fail silently.
        """
        try:
            index = self.get_index_for_name(name)
            del self._priority[index]
            del self._data[name]
        except ValueError:
            if strict:
                raise

    def _sort(self):
        """
        Sort the registry by priority from highest to lowest.

        This method is called internally and should never be explicitly called.
        """
        if not self._is_sorted:
            self._priority.sort(key=lambda item: item.priority, reverse=True)
            self._is_sorted = True