"""One HTML5 repair policy shared by extraction and backfilling."""
import re
from bs4 import BeautifulSoup, NavigableString, Tag

BLOCK_TAGS = {'p', 'h1', 'h2', 'h3', 'h4', 'h5', 'h6', 'li', 'div',
              'section', 'article', 'blockquote', 'table', 'tr', 'td', 'th',
              'ul', 'ol', 'dl', 'dt', 'dd', 'figure', 'figcaption', 'pre'}
TARGET_TAGS = {'p', 'h1', 'h2', 'h3', 'h4', 'h5', 'h6', 'li', 'td', 'th',
               'dt', 'dd', 'figcaption', 'blockquote', 'div', 'section', 'article'}
SKIP_TAGS = {'script', 'style', 'pre', 'code', 'math', 'svg', 'textarea'}


def parse_html(content):
    return BeautifulSoup(re.sub(r'^\s*<\?xml[^>]*\?>', '', content), 'html5lib')


def normalize_navigation_markup(soup):
    """Remove only our generated wrappers around nested NAV labels.

    Reader TOC parsers expect li > a + ol. A generated li > span > a
    retains a valid href but is interpreted as an unlinked section by Calibre.
    This also upgrades source structures cached by earlier versions.
    """
    for wrapper in list(soup.find_all('span', attrs={'data-translation-unit': 'true'})):
        parent = wrapper.parent
        if (parent and parent.name == 'li' and wrapper.find_parent('nav')
                and parent.find('ol', recursive=False)
                and wrapper.find('a', href=True, recursive=False)):
            wrapper.unwrap()


def translation_targets(soup):
    """Choose disjoint leaf blocks; wrap mixed direct text without renaming containers.

    A li containing p must never be extracted twice. Text before a nested list or
    inside an otherwise bare body still needs its own unit.
    """
    normalize_navigation_markup(soup)
    for container in list(soup.find_all(list(TARGET_TAGS | {'body'}))):
        if container.find_parent(list(SKIP_TAGS)) or container.find_parent('nav'):
            continue
        has_blocks = container.find(list(BLOCK_TAGS)) is not None
        if container.name != 'body' and not has_blocks:
            continue
        run = []
        def flush():
            if run and any(isinstance(x, NavigableString) and x.strip() or
                           isinstance(x, Tag) and x.get_text(strip=True) for x in run):
                wrapper = soup.new_tag('span')
                wrapper['data-translation-unit'] = 'true'
                run[0].insert_before(wrapper)
                for node in run:
                    wrapper.append(node.extract())
            run.clear()
        for child in list(container.children):
            if isinstance(child, Tag) and (child.name in BLOCK_TAGS | SKIP_TAGS or child.get('data-translation-unit') == 'true' or child.find(list(BLOCK_TAGS))):
                flush()
            else:
                run.append(child)
        flush()
    return [tag for tag in soup.find_all(True)
            if (tag.get('data-translation-unit') == 'true' or
                tag.name in TARGET_TAGS and not tag.find(list(BLOCK_TAGS)))
            and not tag.find_parent(list(SKIP_TAGS))
            and not tag.find_parent(attrs={'data-translation-unit': 'true'})]