#!/usr/bin/env python
# -*- coding: utf8 -*-
# :Copyright: © 2020 Günter Milde.
# :License: Released under the terms of the `2-Clause BSD license`_, in short:
#
#    Copying and distribution of this file, with or without modification,
#    are permitted in any medium without royalty provided the copyright
#    notice and this notice are preserved.
#    This file is offered as-is, without any warranty.
#
# .. _2-Clause BSD license: https://opensource.org/licenses/BSD-2-Clause
#
# Revision: $Revision$
# Date: $Date$
"""
A parser for CommonMark MarkDown text using `recommonmark`__.

__ https://pypi.org/project/recommonmark/
"""

import docutils.parsers
from docutils import nodes, Component

try:
    from recommonmark.parser import CommonMarkParser
    # from recommonmark.transform import AutoStructify
except ImportError as err:
    CommonMarkParser = None
    class Parser(docutils.parsers.Parser):
        def parse(self, inputstring, document):
            error = document.reporter.warning(
                'Missing dependency: MarkDown input is processed by a 3rd '
                'party parser but Python did not find the required module '
                '"recommonmark" (https://pypi.org/project/recommonmark/).')
            document.append(error)


if CommonMarkParser:
    class Parser(CommonMarkParser):
        """MarkDown parser based on recommonmark."""
        # TODO: settings for AutoStructify
        # settings_spec = docutils.parsers.Parser.settings_spec + (
        # see https://recommonmark.readthedocs.io/en/latest/#autostructify

        supported = ('recommonmark', 'commonmark', 'markdown', 'md')
        config_section = 'recommonmark parser'
        config_section_dependencies = ('parsers',)

        # def get_transforms(self):
        #     return Component.get_transforms(self) + [AutoStructify]

        def parse(self, inputstring, document):
            """Use the upstream parser and clean up afterwards.
            """
            # check for exorbitantly long lines
            for i, line in enumerate(inputstring.split('\n')):
                if len(line) > document.settings.line_length_limit:
                    error = document.reporter.error(
                        'Line %d exceeds the line-length-limit.'%(i+1))
                    document.append(error)
                    return

            # pass to upstream parser
            try:
                CommonMarkParser.parse(self, inputstring, document)
            except Exception as err:
                error = document.reporter.error('Parsing with "recommonmark" '
                                                'returned the error:\n%s'%err)
                document.append(error)

            # Post-Processing
            # ---------------

            # merge adjoining Text nodes:
            for node in document.traverse(nodes.TextElement):
                children = node.children
                i = 0
                while i+1 < len(children):
                    if (isinstance(children[i], nodes.Text)
                        and isinstance(children[i+1], nodes.Text)):
                        children[i] = nodes.Text(children[i]+children.pop(i+1))
                        children[i].parent = node
                    else:
                        i += 1

            # add "code" class argument to inline literal (code spans)
            for node in document.traverse(lambda n: isinstance(n,
                                    (nodes.literal, nodes.literal_block))):
                node['classes'].append('code')
            # move "language" argument to classes
            for node in document.traverse(nodes.literal_block):
                if 'language' in node.attributes:
                    node['classes'].append(node['language'])
                    del node['language']

            # remove empty target nodes
            for node in document.traverse(nodes.target):
                # remove empty name
                node['names'] = [v for v in node['names'] if v]
                if node.children or [v for v in node.attributes.values() if v]:
                    continue
                node.parent.remove(node)

            # replace raw nodes if raw is not allowed
            if not document.settings.raw_enabled:
                for node in document.traverse(nodes.raw):
                    warning = document.reporter.warning('Raw content disabled.')
                    node.parent.replace(node, warning)

            # fix section nodes
            for node in document.traverse(nodes.section):
                # remove spurious IDs (first may be from duplicate name)
                if len(node['ids']) > 1:
                    node['ids'].pop()
                # fix section levels
                section_level = self.get_section_level(node)
                if node['level'] != section_level:
                    warning = document.reporter.warning(
                        'Title level inconsistent. Changing from %d to %d.'
                        %(node['level'], section_level),
                        nodes.literal_block('', node[0].astext()))
                    node.insert(1, warning)
                # remove non-standard attribute "level"
                del node['level'] # TODO: store the original md level somewhere

        def get_section_level(self, node):
            level = 1
            while True:
                node = node.parent
                if isinstance(node, nodes.document):
                    return level
                if isinstance(node, nodes.section):
                    level += 1
