from bs4 import BeautifulSoup, Comment, Doctype, NavigableString, Tag
from textwrap import fill
import re
import six


# General-purpose regex patterns
re_convert_heading = re.compile(r'convert_h(\d+)')
re_line_with_content = re.compile(r'^(.*)', flags=re.MULTILINE)
re_whitespace = re.compile(r'[\t ]+')
re_all_whitespace = re.compile(r'[\t \r\n]+')
re_newline_whitespace = re.compile(r'[\t \r\n]*[\r\n][\t \r\n]*')
re_html_heading = re.compile(r'h(\d+)')

# Pattern for creating convert_<tag> function names from tag names
re_make_convert_fn_name = re.compile(r'[\[\]:-]')

# Extract (leading_nl, content, trailing_nl) from a string
# (functionally equivalent to r'^(\n*)(.*?)(\n*)$', but greedy is faster than reluctant here)
re_extract_newlines = re.compile(r'^(\n*)((?:.*[^\n])?)(\n*)$', flags=re.DOTALL)

# Escape miscellaneous special Markdown characters
re_escape_misc_chars = re.compile(r'([]\\&<`[>~=+|])')

# Escape sequence of one or more consecutive '-', preceded
# and followed by whitespace or start/end of fragment, as it
# might be confused with an underline of a header, or with a
# list marker
re_escape_misc_dash_sequences = re.compile(r'(\s|^)(-+(?:\s|$))')

# Escape sequence of up to six consecutive '#', preceded
# and followed by whitespace or start/end of fragment, as
# it might be confused with an ATX heading
re_escape_misc_hashes = re.compile(r'(\s|^)(#{1,6}(?:\s|$))')

# Escape '.' or ')' preceded by up to nine digits, as it might be
# confused with a list item
re_escape_misc_list_items = re.compile(r'((?:\s|^)[0-9]{1,9})([.)](?:\s|$))')

# Heading styles
ATX = 'atx'
ATX_CLOSED = 'atx_closed'
UNDERLINED = 'underlined'
SETEXT = UNDERLINED

# Newline style
SPACES = 'spaces'
BACKSLASH = 'backslash'

# Strong and emphasis style
ASTERISK = '*'
UNDERSCORE = '_'

# Document strip styles
LSTRIP = 'lstrip'
RSTRIP = 'rstrip'
STRIP = 'strip'


def chomp(text):
    """
    If the text in an inline tag like b, a, or em contains a leading or trailing
    space, strip the string and return a space as suffix of prefix, if needed.
    This function is used to prevent conversions like
        <b> foo</b> => ** foo**
    """
    prefix = ' ' if text and text[0] == ' ' else ''
    suffix = ' ' if text and text[-1] == ' ' else ''
    text = text.strip()
    return (prefix, suffix, text)


def abstract_inline_conversion(markup_fn):
    """
    This abstracts all simple inline tags like b, em, del, ...
    Returns a function that wraps the chomped text in a pair of the string
    that is returned by markup_fn, with '/' inserted in the string used after
    the text if it looks like an HTML tag. markup_fn is necessary to allow for
    references to self.strong_em_symbol etc.
    """
    def implementation(self, el, text, parent_tags):
        markup_prefix = markup_fn(self)
        if markup_prefix.startswith('<') and markup_prefix.endswith('>'):
            markup_suffix = '</' + markup_prefix[1:]
        else:
            markup_suffix = markup_prefix
        if '_noformat' in parent_tags:
            return text
        prefix, suffix, text = chomp(text)
        if not text:
            return ''
        return '%s%s%s%s%s' % (prefix, markup_prefix, text, markup_suffix, suffix)
    return implementation


def _todict(obj):
    return dict((k, getattr(obj, k)) for k in dir(obj) if not k.startswith('_'))


def should_remove_whitespace_inside(el):
    """Return to remove whitespace immediately inside a block-level element."""
    if not el or not el.name:
        return False
    if re_html_heading.match(el.name) is not None:
        return True
    return el.name in ('p', 'blockquote',
                       'article', 'div', 'section',
                       'ol', 'ul', 'li',
                       'table', 'thead', 'tbody', 'tfoot',
                       'tr', 'td', 'th')


def should_remove_whitespace_outside(el):
    """Return to remove whitespace immediately outside a block-level element."""
    return should_remove_whitespace_inside(el) or (el and el.name == 'pre')


def _is_block_content_element(el):
    """
    In a block context, returns:

    - True for content elements (tags and non-whitespace text)
    - False for non-content elements (whitespace text, comments, doctypes)
    """
    if isinstance(el, Tag):
        return True
    elif isinstance(el, (Comment, Doctype)):
        return False  # (subclasses of NavigableString, must test first)
    elif isinstance(el, NavigableString):
        return el.strip() != ''
    else:
        return False


def _prev_block_content_sibling(el):
    """Returns the first previous sibling that is a content element, else None."""
    while el is not None:
        el = el.previous_sibling
        if _is_block_content_element(el):
            return el
    return None


def _next_block_content_sibling(el):
    """Returns the first next sibling that is a content element, else None."""
    while el is not None:
        el = el.next_sibling
        if _is_block_content_element(el):
            return el
    return None


class MarkdownConverter(object):
    class DefaultOptions:
        autolinks = True
        bullets = '*+-'  # An iterable of bullet types.
        code_language = ''
        code_language_callback = None
        convert = None
        default_title = False
        escape_asterisks = True
        escape_underscores = True
        escape_misc = False
        heading_style = UNDERLINED
        keep_inline_images_in = []
        newline_style = SPACES
        strip = None
        strip_document = STRIP
        strong_em_symbol = ASTERISK
        sub_symbol = ''
        sup_symbol = ''
        table_infer_header = False
        wrap = False
        wrap_width = 80

    class Options(DefaultOptions):
        pass

    def __init__(self, **options):
        # Create an options dictionary. Use DefaultOptions as a base so that
        # it doesn't have to be extended.
        self.options = _todict(self.DefaultOptions)
        self.options.update(_todict(self.Options))
        self.options.update(options)
        if self.options['strip'] is not None and self.options['convert'] is not None:
            raise ValueError('You may specify either tags to strip or tags to'
                             ' convert, but not both.')

        # Initialize the conversion function cache
        self.convert_fn_cache = {}

    def convert(self, html):
        soup = BeautifulSoup(html, 'html.parser')
        return self.convert_soup(soup)

    def convert_soup(self, soup):
        return self.process_tag(soup, parent_tags=set())

    def process_element(self, node, parent_tags=None):
        if isinstance(node, NavigableString):
            return self.process_text(node, parent_tags=parent_tags)
        else:
            return self.process_tag(node, parent_tags=parent_tags)

    def process_tag(self, node, parent_tags=None):
        # For the top-level element, initialize the parent context with an empty set.
        if parent_tags is None:
            parent_tags = set()

        # Collect child elements to process, ignoring whitespace-only text elements
        # adjacent to the inner/outer boundaries of block elements.
        should_remove_inside = should_remove_whitespace_inside(node)

        def _can_ignore(el):
            if isinstance(el, Tag):
                # Tags are always processed.
                return False
            elif isinstance(el, (Comment, Doctype)):
                # Comment and Doctype elements are always ignored.
                # (subclasses of NavigableString, must test first)
                return True
            elif isinstance(el, NavigableString):
                if six.text_type(el).strip() != '':
                    # Non-whitespace text nodes are always processed.
                    return False
                elif should_remove_inside and (not el.previous_sibling or not el.next_sibling):
                    # Inside block elements (excluding <pre>), ignore adjacent whitespace elements.
                    return True
                elif should_remove_whitespace_outside(el.previous_sibling) or should_remove_whitespace_outside(el.next_sibling):
                    # Outside block elements (including <pre>), ignore adjacent whitespace elements.
                    return True
                else:
                    return False
            elif el is None:
                return True
            else:
                raise ValueError('Unexpected element type: %s' % type(el))

        children_to_convert = [el for el in node.children if not _can_ignore(el)]

        # Create a copy of this tag's parent context, then update it to include this tag
        # to propagate down into the children.
        parent_tags_for_children = set(parent_tags)
        parent_tags_for_children.add(node.name)

        # if this tag is a heading or table cell, add an '_inline' parent pseudo-tag
        if (
            re_html_heading.match(node.name) is not None  # headings
            or node.name in {'td', 'th'}  # table cells
        ):
            parent_tags_for_children.add('_inline')

        # if this tag is a preformatted element, add a '_noformat' parent pseudo-tag
        if node.name in {'pre', 'code', 'kbd', 'samp'}:
            parent_tags_for_children.add('_noformat')

        # Convert the children elements into a list of result strings.
        child_strings = [
            self.process_element(el, parent_tags=parent_tags_for_children)
            for el in children_to_convert
        ]

        # Remove empty string values.
        child_strings = [s for s in child_strings if s]

        # Collapse newlines at child element boundaries, if needed.
        if node.name == 'pre' or node.find_parent('pre'):
            # Inside <pre> blocks, do not collapse newlines.
            pass
        else:
            # Collapse newlines at child element boundaries.
            updated_child_strings = ['']  # so the first lookback works
            for child_string in child_strings:
                # Separate the leading/trailing newlines from the content.
                leading_nl, content, trailing_nl = re_extract_newlines.match(child_string).groups()

                # If the last child had trailing newlines and this child has leading newlines,
                # use the larger newline count, limited to 2.
                if updated_child_strings[-1] and leading_nl:
                    prev_trailing_nl = updated_child_strings.pop()  # will be replaced by the collapsed value
                    num_newlines = min(2, max(len(prev_trailing_nl), len(leading_nl)))
                    leading_nl = '\n' * num_newlines

                # Add the results to the updated child string list.
                updated_child_strings.extend([leading_nl, content, trailing_nl])

            child_strings = updated_child_strings

        # Join all child text strings into a single string.
        text = ''.join(child_strings)

        # apply this tag's final conversion function
        convert_fn = self.get_conv_fn_cached(node.name)
        if convert_fn is not None:
            text = convert_fn(node, text, parent_tags=parent_tags)

        return text

    def convert__document_(self, el, text, parent_tags):
        """Final document-level formatting for BeautifulSoup object (node.name == "[document]")"""
        if self.options['strip_document'] == LSTRIP:
            text = text.lstrip('\n')  # remove leading separation newlines
        elif self.options['strip_document'] == RSTRIP:
            text = text.rstrip('\n')  # remove trailing separation newlines
        elif self.options['strip_document'] == STRIP:
            text = text.strip('\n')  # remove leading and trailing separation newlines
        elif self.options['strip_document'] is None:
            pass  # leave leading and trailing separation newlines as-is
        else:
            raise ValueError('Invalid value for strip_document: %s' % self.options['strip_document'])

        return text

    def process_text(self, el, parent_tags=None):
        # For the top-level element, initialize the parent context with an empty set.
        if parent_tags is None:
            parent_tags = set()

        text = six.text_type(el) or ''

        # normalize whitespace if we're not inside a preformatted element
        if 'pre' not in parent_tags:
            if self.options['wrap']:
                text = re_all_whitespace.sub(' ', text)
            else:
                text = re_newline_whitespace.sub('\n', text)
                text = re_whitespace.sub(' ', text)

        # escape special characters if we're not inside a preformatted or code element
        if '_noformat' not in parent_tags:
            text = self.escape(text, parent_tags)

        # remove leading whitespace at the start or just after a
        # block-level element; remove traliing whitespace at the end
        # or just before a block-level element.
        if (should_remove_whitespace_outside(el.previous_sibling)
                or (should_remove_whitespace_inside(el.parent)
                    and not el.previous_sibling)):
            text = text.lstrip(' \t\r\n')
        if (should_remove_whitespace_outside(el.next_sibling)
                or (should_remove_whitespace_inside(el.parent)
                    and not el.next_sibling)):
            text = text.rstrip()

        return text

    def get_conv_fn_cached(self, tag_name):
        """Given a tag name, return the conversion function using the cache."""
        # If conversion function is not in cache, add it
        if tag_name not in self.convert_fn_cache:
            self.convert_fn_cache[tag_name] = self.get_conv_fn(tag_name)

        # Return the cached entry
        return self.convert_fn_cache[tag_name]

    def get_conv_fn(self, tag_name):
        """Given a tag name, find and return the conversion function."""
        tag_name = tag_name.lower()

        # Handle strip/convert exclusion options
        if not self.should_convert_tag(tag_name):
            return None

        # Handle headings with _convert_hn() function
        match = re_html_heading.match(tag_name)
        if match:
            n = int(match.group(1))
            return lambda el, text, parent_tags: self._convert_hn(n, el, text, parent_tags)

        # For other tags, look up their conversion function by tag name
        convert_fn_name = "convert_%s" % re_make_convert_fn_name.sub('_', tag_name)
        convert_fn = getattr(self, convert_fn_name, None)
        return convert_fn

    def should_convert_tag(self, tag):
        """Given a tag name, return whether to convert based on strip/convert options."""
        strip = self.options['strip']
        convert = self.options['convert']
        if strip is not None:
            return tag not in strip
        elif convert is not None:
            return tag in convert
        else:
            return True

    def escape(self, text, parent_tags):
        if not text:
            return ''
        if self.options['escape_misc']:
            text = re_escape_misc_chars.sub(r'\\\1', text)
            text = re_escape_misc_dash_sequences.sub(r'\1\\\2', text)
            text = re_escape_misc_hashes.sub(r'\1\\\2', text)
            text = re_escape_misc_list_items.sub(r'\1\\\2', text)

        if self.options['escape_asterisks']:
            text = text.replace('*', r'\*')
        if self.options['escape_underscores']:
            text = text.replace('_', r'\_')
        return text

    def underline(self, text, pad_char):
        text = (text or '').rstrip()
        return '\n\n%s\n%s\n\n' % (text, pad_char * len(text)) if text else ''

    def convert_a(self, el, text, parent_tags):
        if '_noformat' in parent_tags:
            return text
        prefix, suffix, text = chomp(text)
        if not text:
            return ''
        href = el.get('href')
        title = el.get('title')
        # For the replacement see #29: text nodes underscores are escaped
        if (self.options['autolinks']
                and text.replace(r'\_', '_') == href
                and not title
                and not self.options['default_title']):
            # Shortcut syntax
            return '<%s>' % href
        if self.options['default_title'] and not title:
            title = href
        title_part = ' "%s"' % title.replace('"', r'\"') if title else ''
        return '%s[%s](%s%s)%s' % (prefix, text, href, title_part, suffix) if href else text

    convert_b = abstract_inline_conversion(lambda self: 2 * self.options['strong_em_symbol'])

    def convert_blockquote(self, el, text, parent_tags):
        # handle some early-exit scenarios
        text = (text or '').strip(' \t\r\n')
        if '_inline' in parent_tags:
            return ' ' + text + ' '
        if not text:
            return "\n"

        # indent lines with blockquote marker
        def _indent_for_blockquote(match):
            line_content = match.group(1)
            return '> ' + line_content if line_content else '>'
        text = re_line_with_content.sub(_indent_for_blockquote, text)

        return '\n' + text + '\n\n'

    def convert_br(self, el, text, parent_tags):
        if '_inline' in parent_tags:
            return ""

        if self.options['newline_style'].lower() == BACKSLASH:
            return '\\\n'
        else:
            return '  \n'

    def convert_code(self, el, text, parent_tags):
        if 'pre' in parent_tags:
            return text
        converter = abstract_inline_conversion(lambda self: '`')
        return converter(self, el, text, parent_tags)

    convert_del = abstract_inline_conversion(lambda self: '~~')

    def convert_div(self, el, text, parent_tags):
        if '_inline' in parent_tags:
            return ' ' + text.strip() + ' '
        text = text.strip()
        return '\n\n%s\n\n' % text if text else ''

    convert_article = convert_div

    convert_section = convert_div

    convert_em = abstract_inline_conversion(lambda self: self.options['strong_em_symbol'])

    convert_kbd = convert_code

    def convert_dd(self, el, text, parent_tags):
        text = (text or '').strip()
        if '_inline' in parent_tags:
            return ' ' + text + ' '
        if not text:
            return '\n'

        # indent definition content lines by four spaces
        def _indent_for_dd(match):
            line_content = match.group(1)
            return '    ' + line_content if line_content else ''
        text = re_line_with_content.sub(_indent_for_dd, text)

        # insert definition marker into first-line indent whitespace
        text = ':' + text[1:]

        return '%s\n' % text

    def convert_dt(self, el, text, parent_tags):
        # remove newlines from term text
        text = (text or '').strip()
        text = re_all_whitespace.sub(' ', text)
        if '_inline' in parent_tags:
            return ' ' + text + ' '
        if not text:
            return '\n'

        # TODO - format consecutive <dt> elements as directly adjacent lines):
        #   https://michelf.ca/projects/php-markdown/extra/#def-list

        return '\n%s\n' % text

    def _convert_hn(self, n, el, text, parent_tags):
        """ Method name prefixed with _ to prevent <hn> to call this """
        if '_inline' in parent_tags:
            return text

        # prevent MemoryErrors in case of very large n
        n = max(1, min(6, n))

        style = self.options['heading_style'].lower()
        text = text.strip()
        if style == UNDERLINED and n <= 2:
            line = '=' if n == 1 else '-'
            return self.underline(text, line)
        text = re_all_whitespace.sub(' ', text)
        hashes = '#' * n
        if style == ATX_CLOSED:
            return '\n\n%s %s %s\n\n' % (hashes, text, hashes)
        return '\n\n%s %s\n\n' % (hashes, text)

    def convert_hr(self, el, text, parent_tags):
        return '\n\n---\n\n'

    convert_i = convert_em

    def convert_img(self, el, text, parent_tags):
        alt = el.attrs.get('alt', None) or ''
        src = el.attrs.get('src', None) or ''
        title = el.attrs.get('title', None) or ''
        title_part = ' "%s"' % title.replace('"', r'\"') if title else ''
        if ('_inline' in parent_tags
                and el.parent.name not in self.options['keep_inline_images_in']):
            return alt

        return '![%s](%s%s)' % (alt, src, title_part)

    def convert_list(self, el, text, parent_tags):

        # Converting a list to inline is undefined.
        # Ignoring inline conversion parents for list.

        before_paragraph = False
        next_sibling = _next_block_content_sibling(el)
        if next_sibling and next_sibling.name not in ['ul', 'ol']:
            before_paragraph = True
        if 'li' in parent_tags:
            # remove trailing newline if we're in a nested list
            return '\n' + text.rstrip()
        return '\n\n' + text + ('\n' if before_paragraph else '')

    convert_ul = convert_list
    convert_ol = convert_list

    def convert_li(self, el, text, parent_tags):
        # handle some early-exit scenarios
        text = (text or '').strip()
        if not text:
            return "\n"

        # determine list item bullet character to use
        parent = el.parent
        if parent is not None and parent.name == 'ol':
            if parent.get("start") and str(parent.get("start")).isnumeric():
                start = int(parent.get("start"))
            else:
                start = 1
            bullet = '%s.' % (start + len(el.find_previous_siblings('li')))
        else:
            depth = -1
            while el:
                if el.name == 'ul':
                    depth += 1
                el = el.parent
            bullets = self.options['bullets']
            bullet = bullets[depth % len(bullets)]
        bullet = bullet + ' '
        bullet_width = len(bullet)
        bullet_indent = ' ' * bullet_width

        # indent content lines by bullet width
        def _indent_for_li(match):
            line_content = match.group(1)
            return bullet_indent + line_content if line_content else ''
        text = re_line_with_content.sub(_indent_for_li, text)

        # insert bullet into first-line indent whitespace
        text = bullet + text[bullet_width:]

        return '%s\n' % text

    def convert_p(self, el, text, parent_tags):
        if '_inline' in parent_tags:
            return ' ' + text.strip(' \t\r\n') + ' '
        text = text.strip(' \t\r\n')
        if self.options['wrap']:
            # Preserve newlines (and preceding whitespace) resulting
            # from <br> tags.  Newlines in the input have already been
            # replaced by spaces.
            if self.options['wrap_width'] is not None:
                lines = text.split('\n')
                new_lines = []
                for line in lines:
                    line = line.lstrip(' \t\r\n')
                    line_no_trailing = line.rstrip()
                    trailing = line[len(line_no_trailing):]
                    line = fill(line,
                                width=self.options['wrap_width'],
                                break_long_words=False,
                                break_on_hyphens=False)
                    new_lines.append(line + trailing)
                text = '\n'.join(new_lines)
        return '\n\n%s\n\n' % text if text else ''

    def convert_pre(self, el, text, parent_tags):
        if not text:
            return ''
        code_language = self.options['code_language']

        if self.options['code_language_callback']:
            code_language = self.options['code_language_callback'](el) or code_language

        return '\n\n```%s\n%s\n```\n\n' % (code_language, text)

    def convert_script(self, el, text, parent_tags):
        return ''

    def convert_style(self, el, text, parent_tags):
        return ''

    convert_s = convert_del

    convert_strong = convert_b

    convert_samp = convert_code

    convert_sub = abstract_inline_conversion(lambda self: self.options['sub_symbol'])

    convert_sup = abstract_inline_conversion(lambda self: self.options['sup_symbol'])

    def convert_table(self, el, text, parent_tags):
        return '\n\n' + text.strip() + '\n\n'

    def convert_caption(self, el, text, parent_tags):
        return text.strip() + '\n\n'

    def convert_figcaption(self, el, text, parent_tags):
        return '\n\n' + text.strip() + '\n\n'

    def convert_td(self, el, text, parent_tags):
        colspan = 1
        if 'colspan' in el.attrs and el['colspan'].isdigit():
            colspan = int(el['colspan'])
        return ' ' + text.strip().replace("\n", " ") + ' |' * colspan

    def convert_th(self, el, text, parent_tags):
        colspan = 1
        if 'colspan' in el.attrs and el['colspan'].isdigit():
            colspan = int(el['colspan'])
        return ' ' + text.strip().replace("\n", " ") + ' |' * colspan

    def convert_tr(self, el, text, parent_tags):
        cells = el.find_all(['td', 'th'])
        is_first_row = el.find_previous_sibling() is None
        is_headrow = (
            all([cell.name == 'th' for cell in cells])
            or (el.parent.name == 'thead'
                # avoid multiple tr in thead
                and len(el.parent.find_all('tr')) == 1)
        )
        is_head_row_missing = (
            (is_first_row and not el.parent.name == 'tbody')
            or (is_first_row and el.parent.name == 'tbody' and len(el.parent.parent.find_all(['thead'])) < 1)
        )
        overline = ''
        underline = ''
        if ((is_headrow
             or (is_head_row_missing
                 and self.options['table_infer_header']))
                and is_first_row):
            # first row and:
            # - is headline or
            # - headline is missing and header inference is enabled
            # print headline underline
            full_colspan = 0
            for cell in cells:
                if 'colspan' in cell.attrs and cell['colspan'].isdigit():
                    full_colspan += int(cell["colspan"])
                else:
                    full_colspan += 1
            underline += '| ' + ' | '.join(['---'] * full_colspan) + ' |' + '\n'
        elif ((is_head_row_missing
               and not self.options['table_infer_header'])
              or (is_first_row
                  and (el.parent.name == 'table'
                       or (el.parent.name == 'tbody'
                           and not el.parent.find_previous_sibling())))):
            # headline is missing and header inference is disabled or:
            # first row, not headline, and:
            #  - the parent is table or
            #  - the parent is tbody at the beginning of a table.
            # print empty headline above this row
            overline += '| ' + ' | '.join([''] * len(cells)) + ' |' + '\n'
            overline += '| ' + ' | '.join(['---'] * len(cells)) + ' |' + '\n'
        return overline + '|' + text + '\n' + underline


def markdownify(html, **options):
    return MarkdownConverter(**options).convert(html)