"""
    sphinx.environment.collectors.title
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    The title collector components for sphinx.environment.

    :copyright: Copyright 2007-2021 by the Sphinx team, see AUTHORS.
    :license: BSD, see LICENSE for details.
"""

from typing import Any, Dict, Set

from docutils import nodes

from sphinx.application import Sphinx
from sphinx.environment import BuildEnvironment
from sphinx.environment.collectors import EnvironmentCollector
from sphinx.transforms import SphinxContentsFilter


class TitleCollector(EnvironmentCollector):
    """title collector for sphinx.environment."""

    def clear_doc(self, app: Sphinx, env: BuildEnvironment, docname: str) -> None:
        env.titles.pop(docname, None)
        env.longtitles.pop(docname, None)

    def merge_other(self, app: Sphinx, env: BuildEnvironment,
                    docnames: Set[str], other: BuildEnvironment) -> None:
        for docname in docnames:
            env.titles[docname] = other.titles[docname]
            env.longtitles[docname] = other.longtitles[docname]

    def process_doc(self, app: Sphinx, doctree: nodes.document) -> None:
        """Add a title node to the document (just copy the first section title),
        and store that title in the environment.
        """
        titlenode = nodes.title()
        longtitlenode = titlenode
        # explicit title set with title directive; use this only for
        # the <title> tag in HTML output
        if 'title' in doctree:
            longtitlenode = nodes.title()
            longtitlenode += nodes.Text(doctree['title'])
        # look for first section title and use that as the title
        for node in doctree.traverse(nodes.section):
            visitor = SphinxContentsFilter(doctree)
            node[0].walkabout(visitor)
            titlenode += visitor.get_entry_text()
            break
        else:
            # document has no title
            titlenode += nodes.Text(doctree.get('title', '<no title>'))
        app.env.titles[app.env.docname] = titlenode
        app.env.longtitles[app.env.docname] = longtitlenode


def setup(app: Sphinx) -> Dict[str, Any]:
    app.add_env_collector(TitleCollector)

    return {
        'version': 'builtin',
        'parallel_read_safe': True,
        'parallel_write_safe': True,
    }