"""
Table of Contents Extension for Python-Markdown
===============================================

See <https://Python-Markdown.github.io/extensions/toc>
for documentation.

Original code Copyright 2008 [Jack Miller](https://codezen.org/)

All changes Copyright 2008-2014 The Python Markdown Project

License: [BSD](https://opensource.org/licenses/bsd-license.php)

"""

from . import Extension
from ..treeprocessors import Treeprocessor
from ..util import code_escape, parseBoolValue, AMP_SUBSTITUTE, HTML_PLACEHOLDER_RE, AtomicString
from ..treeprocessors import UnescapeTreeprocessor
import re
import html
import unicodedata
import xml.etree.ElementTree as etree


def slugify(value, separator, unicode=False):
    """ Slugify a string, to make it URL friendly. """
    if not unicode:
        # Replace Extended Latin characters with ASCII, i.e. `žlutý` => `zluty`
        value = unicodedata.normalize('NFKD', value)
        value = value.encode('ascii', 'ignore').decode('ascii')
    value = re.sub(r'[^\w\s-]', '', value).strip().lower()
    return re.sub(r'[{}\s]+'.format(separator), separator, value)


def slugify_unicode(value, separator):
    """ Slugify a string, to make it URL friendly while preserving Unicode characters. """
    return slugify(value, separator, unicode=True)


IDCOUNT_RE = re.compile(r'^(.*)_([0-9]+)$')


def unique(id, ids):
    """ Ensure id is unique in set of ids. Append '_1', '_2'... if not """
    while id in ids or not id:
        m = IDCOUNT_RE.match(id)
        if m:
            id = '%s_%d' % (m.group(1), int(m.group(2))+1)
        else:
            id = '%s_%d' % (id, 1)
    ids.add(id)
    return id


def get_name(el):
    """Get title name."""

    text = []
    for c in el.itertext():
        if isinstance(c, AtomicString):
            text.append(html.unescape(c))
        else:
            text.append(c)
    return ''.join(text).strip()


def stashedHTML2text(text, md, strip_entities=True):
    """ Extract raw HTML from stash, reduce to plain text and swap with placeholder. """
    def _html_sub(m):
        """ Substitute raw html with plain text. """
        try:
            raw = md.htmlStash.rawHtmlBlocks[int(m.group(1))]
        except (IndexError, TypeError):  # pragma: no cover
            return m.group(0)
        # Strip out tags and/or entities - leaving text
        res = re.sub(r'(<[^>]+>)', '', raw)
        if strip_entities:
            res = re.sub(r'(&[\#a-zA-Z0-9]+;)', '', res)
        return res

    return HTML_PLACEHOLDER_RE.sub(_html_sub, text)


def unescape(text):
    """ Unescape escaped text. """
    c = UnescapeTreeprocessor()
    return c.unescape(text)


def nest_toc_tokens(toc_list):
    """Given an unsorted list with errors and skips, return a nested one.
    [{'level': 1}, {'level': 2}]
    =>
    [{'level': 1, 'children': [{'level': 2, 'children': []}]}]

    A wrong list is also converted:
    [{'level': 2}, {'level': 1}]
    =>
    [{'level': 2, 'children': []}, {'level': 1, 'children': []}]
    """

    ordered_list = []
    if len(toc_list):
        # Initialize everything by processing the first entry
        last = toc_list.pop(0)
        last['children'] = []
        levels = [last['level']]
        ordered_list.append(last)
        parents = []

        # Walk the rest nesting the entries properly
        while toc_list:
            t = toc_list.pop(0)
            current_level = t['level']
            t['children'] = []

            # Reduce depth if current level < last item's level
            if current_level < levels[-1]:
                # Pop last level since we know we are less than it
                levels.pop()

                # Pop parents and levels we are less than or equal to
                to_pop = 0
                for p in reversed(parents):
                    if current_level <= p['level']:
                        to_pop += 1
                    else:  # pragma: no cover
                        break
                if to_pop:
                    levels = levels[:-to_pop]
                    parents = parents[:-to_pop]

                # Note current level as last
                levels.append(current_level)

            # Level is the same, so append to
            # the current parent (if available)
            if current_level == levels[-1]:
                (parents[-1]['children'] if parents
                 else ordered_list).append(t)

            # Current level is > last item's level,
            # So make last item a parent and append current as child
            else:
                last['children'].append(t)
                parents.append(last)
                levels.append(current_level)
            last = t

    return ordered_list


class TocTreeprocessor(Treeprocessor):
    def __init__(self, md, config):
        super().__init__(md)

        self.marker = config["marker"]
        self.title = config["title"]
        self.base_level = int(config["baselevel"]) - 1
        self.slugify = config["slugify"]
        self.sep = config["separator"]
        self.toc_class = config["toc_class"]
        self.use_anchors = parseBoolValue(config["anchorlink"])
        self.anchorlink_class = config["anchorlink_class"]
        self.use_permalinks = parseBoolValue(config["permalink"], False)
        if self.use_permalinks is None:
            self.use_permalinks = config["permalink"]
        self.permalink_class = config["permalink_class"]
        self.permalink_title = config["permalink_title"]
        self.header_rgx = re.compile("[Hh][123456]")
        if isinstance(config["toc_depth"], str) and '-' in config["toc_depth"]:
            self.toc_top, self.toc_bottom = [int(x) for x in config["toc_depth"].split('-')]
        else:
            self.toc_top = 1
            self.toc_bottom = int(config["toc_depth"])

    def iterparent(self, node):
        ''' Iterator wrapper to get allowed parent and child all at once. '''

        # We do not allow the marker inside a header as that
        # would causes an endless loop of placing a new TOC
        # inside previously generated TOC.
        for child in node:
            if not self.header_rgx.match(child.tag) and child.tag not in ['pre', 'code']:
                yield node, child
                yield from self.iterparent(child)

    def replace_marker(self, root, elem):
        ''' Replace marker with elem. '''
        for (p, c) in self.iterparent(root):
            text = ''.join(c.itertext()).strip()
            if not text:
                continue

            # To keep the output from screwing up the
            # validation by putting a `<div>` inside of a `<p>`
            # we actually replace the `<p>` in its entirety.

            # The `<p>` element may contain more than a single text content
            # (`nl2br` can introduce a `<br>`). In this situation, `c.text` returns
            # the very first content, ignore children contents or tail content.
            # `len(c) == 0` is here to ensure there is only text in the `<p>`.
            if c.text and c.text.strip() == self.marker and len(c) == 0:
                for i in range(len(p)):
                    if p[i] == c:
                        p[i] = elem
                        break

    def set_level(self, elem):
        ''' Adjust header level according to base level. '''
        level = int(elem.tag[-1]) + self.base_level
        if level > 6:
            level = 6
        elem.tag = 'h%d' % level

    def add_anchor(self, c, elem_id):
        anchor = etree.Element("a")
        anchor.text = c.text
        anchor.attrib["href"] = "#" + elem_id
        anchor.attrib["class"] = self.anchorlink_class
        c.text = ""
        for elem in c:
            anchor.append(elem)
        while len(c):
            c.remove(c[0])
        c.append(anchor)

    def add_permalink(self, c, elem_id):
        permalink = etree.Element("a")
        permalink.text = ("%spara;" % AMP_SUBSTITUTE
                          if self.use_permalinks is True
                          else self.use_permalinks)
        permalink.attrib["href"] = "#" + elem_id
        permalink.attrib["class"] = self.permalink_class
        if self.permalink_title:
            permalink.attrib["title"] = self.permalink_title
        c.append(permalink)

    def build_toc_div(self, toc_list):
        """ Return a string div given a toc list. """
        div = etree.Element("div")
        div.attrib["class"] = self.toc_class

        # Add title to the div
        if self.title:
            header = etree.SubElement(div, "span")
            header.attrib["class"] = "toctitle"
            header.text = self.title

        def build_etree_ul(toc_list, parent):
            ul = etree.SubElement(parent, "ul")
            for item in toc_list:
                # List item link, to be inserted into the toc div
                li = etree.SubElement(ul, "li")
                link = etree.SubElement(li, "a")
                link.text = item.get('name', '')
                link.attrib["href"] = '#' + item.get('id', '')
                if item['children']:
                    build_etree_ul(item['children'], li)
            return ul

        build_etree_ul(toc_list, div)

        if 'prettify' in self.md.treeprocessors:
            self.md.treeprocessors['prettify'].run(div)

        return div

    def run(self, doc):
        # Get a list of id attributes
        used_ids = set()
        for el in doc.iter():
            if "id" in el.attrib:
                used_ids.add(el.attrib["id"])

        toc_tokens = []
        for el in doc.iter():
            if isinstance(el.tag, str) and self.header_rgx.match(el.tag):
                self.set_level(el)
                text = get_name(el)

                # Do not override pre-existing ids
                if "id" not in el.attrib:
                    innertext = unescape(stashedHTML2text(text, self.md))
                    el.attrib["id"] = unique(self.slugify(innertext, self.sep), used_ids)

                if int(el.tag[-1]) >= self.toc_top and int(el.tag[-1]) <= self.toc_bottom:
                    toc_tokens.append({
                        'level': int(el.tag[-1]),
                        'id': el.attrib["id"],
                        'name': unescape(stashedHTML2text(
                            code_escape(el.attrib.get('data-toc-label', text)),
                            self.md, strip_entities=False
                        ))
                    })

                # Remove the data-toc-label attribute as it is no longer needed
                if 'data-toc-label' in el.attrib:
                    del el.attrib['data-toc-label']

                if self.use_anchors:
                    self.add_anchor(el, el.attrib["id"])
                if self.use_permalinks not in [False, None]:
                    self.add_permalink(el, el.attrib["id"])

        toc_tokens = nest_toc_tokens(toc_tokens)
        div = self.build_toc_div(toc_tokens)
        if self.marker:
            self.replace_marker(doc, div)

        # serialize and attach to markdown instance.
        toc = self.md.serializer(div)
        for pp in self.md.postprocessors:
            toc = pp.run(toc)
        self.md.toc_tokens = toc_tokens
        self.md.toc = toc


class TocExtension(Extension):

    TreeProcessorClass = TocTreeprocessor

    def __init__(self, **kwargs):
        self.config = {
            "marker": ['[TOC]',
                       'Text to find and replace with Table of Contents - '
                       'Set to an empty string to disable. Defaults to "[TOC]"'],
            "title": ["",
                      "Title to insert into TOC <div> - "
                      "Defaults to an empty string"],
            "toc_class": ['toc',
                          'CSS class(es) used for the link. '
                          'Defaults to "toclink"'],
            "anchorlink": [False,
                           "True if header should be a self link - "
                           "Defaults to False"],
            "anchorlink_class": ['toclink',
                                 'CSS class(es) used for the link. '
                                 'Defaults to "toclink"'],
            "permalink": [0,
                          "True or link text if a Sphinx-style permalink should "
                          "be added - Defaults to False"],
            "permalink_class": ['headerlink',
                                'CSS class(es) used for the link. '
                                'Defaults to "headerlink"'],
            "permalink_title": ["Permanent link",
                                "Title attribute of the permalink - "
                                "Defaults to 'Permanent link'"],
            "baselevel": ['1', 'Base level for headers.'],
            "slugify": [slugify,
                        "Function to generate anchors based on header text - "
                        "Defaults to the headerid ext's slugify function."],
            'separator': ['-', 'Word separator. Defaults to "-".'],
            "toc_depth": [6,
                          'Define the range of section levels to include in'
                          'the Table of Contents. A single integer (b) defines'
                          'the bottom section level (<h1>..<hb>) only.'
                          'A string consisting of two digits separated by a hyphen'
                          'in between ("2-5"), define the top (t) and the'
                          'bottom (b) (<ht>..<hb>). Defaults to `6` (bottom).'],
        }

        super().__init__(**kwargs)

    def extendMarkdown(self, md):
        md.registerExtension(self)
        self.md = md
        self.reset()
        tocext = self.TreeProcessorClass(md, self.getConfigs())
        md.treeprocessors.register(tocext, 'toc', 5)

    def reset(self):
        self.md.toc = ''
        self.md.toc_tokens = []


def makeExtension(**kwargs):  # pragma: no cover
    return TocExtension(**kwargs)
