"""reStructuredText helper functions."""

from __future__ import annotations

import re
from collections import defaultdict
from contextlib import contextmanager
from typing import TYPE_CHECKING
from unicodedata import east_asian_width

from docutils.parsers.rst import roles
from docutils.parsers.rst.languages import en as english
from docutils.parsers.rst.states import Body
from docutils.utils import Reporter
from jinja2 import pass_environment

from sphinx.locale import __
from sphinx.util import docutils, logging

if TYPE_CHECKING:
    from collections.abc import Iterator

    from docutils.statemachine import StringList
    from jinja2 import Environment

logger = logging.getLogger(__name__)

_FIELD_NAME_RE = re.compile(Body.patterns['field_marker'])
symbols_re = re.compile(r'([!-\-/:-@\[-`{-~])')  # symbols without dot(0x2e)
SECTIONING_CHARS = ['=', '-', '~']

# width of characters
WIDECHARS: dict[str, str] = defaultdict(lambda: 'WF')  # WF: Wide + Full-width
WIDECHARS['ja'] = 'WFA'  # In Japanese, Ambiguous characters also have double width


def escape(text: str) -> str:
    text = symbols_re.sub(r'\\\1', text)
    text = re.sub(r'^\.', r'\.', text)  # escape a dot at top
    return text


def textwidth(text: str, widechars: str = 'WF') -> int:
    """Get width of text."""

    def charwidth(char: str, widechars: str) -> int:
        if east_asian_width(char) in widechars:
            return 2
        else:
            return 1

    return sum(charwidth(c, widechars) for c in text)


@pass_environment
def heading(env: Environment, text: str, level: int = 1) -> str:
    """Create a heading for *level*."""
    assert level <= 3
    # ``env.language`` is injected by ``sphinx.util.template.ReSTRenderer``
    width = textwidth(text, WIDECHARS[env.language])  # type: ignore[attr-defined]
    sectioning_char = SECTIONING_CHARS[level - 1]
    return f'{text}\n{sectioning_char * width}'


@contextmanager
def default_role(docname: str, name: str) -> Iterator[None]:
    if name:
        dummy_reporter = Reporter('', 4, 4)
        role_fn, _ = roles.role(name, english, 0, dummy_reporter)  # type: ignore[arg-type]
        if role_fn:
            docutils.register_role('', role_fn)  # type: ignore[arg-type]
        else:
            logger.warning(__('default role %s not found'), name, location=docname)

    yield

    docutils.unregister_role('')


def _prepend_prologue(content: StringList, prologue: str) -> None:
    """Prepend a string to content body as a prologue."""
    if not prologue:
        return
    pos = 0
    for line in content:
        if _FIELD_NAME_RE.match(line):
            pos += 1
        else:
            break

    if pos > 0:
        # insert a blank line after docinfo
        content.insert(pos, '', '', 0)
        pos += 1

    # insert prologue (after docinfo if exists)
    lineno = 0
    for lineno, line in enumerate(prologue.splitlines()):
        content.insert(pos + lineno, line, '', lineno)

    content.insert(pos + lineno + 1, '', '', 0)


def _append_epilogue(content: StringList, epilogue: str) -> None:
    """Append a string to content body as an epilogue."""
    if not epilogue:
        return
    if len(content) > 0:
        source, lineno = content.items[-1]
    else:
        source = ''
        lineno = 0
    content.append('', source, lineno + 1)
    for lineno, line in enumerate(epilogue.splitlines()):
        content.append(line, '', lineno)