"""
Sphinx inplace translation.
Please put `xxx_zh_CN.rst` alongside `xxx.rst`. When language is set to `zh_CN`,
`xxx_zh_CN.rst` will be used in place of `xxx.rst`.
If translation does not exist, it will automatically fallback to the original files, without warning.

I write this based on the example of:
https://github.com/readthedocs/sphinxcontrib-multisrc/blob/master/sphinxcontrib/multisrc.py
"""

import os
import types


def builder_inited(app):
    """Event listener to set up multiple environments."""
    patch_doc2path(app.env, app.config.language)


def patch_doc2path(env, language):
    # patch doc2path so that it resolves to the correct language.
    override_doc2path = env.doc2path

    def doc2path(env, docname: str, base: bool = True):
        path = override_doc2path(docname, base)
        if language not in (None, 'en'):
            # The language is set to another one
            new_docname = f'{docname}_{language}'
            new_path = override_doc2path(new_docname, base)
            if os.path.exists(new_path):
                return new_path
        return path

    env.doc2path = types.MethodType(doc2path, env)


def setup(app):
    app.connect('builder-inited', builder_inited)