"""The CHANGELOG.md section of one version, the text of its release."""

from __future__ import annotations

import re

#: A version heading in CHANGELOG.md: "## [1.2.3] - 2026-10-01".
_HEADING = re.compile(r"^## \[(?P<version>[^\]]+)\]", re.MULTILINE)


def changelog_section(text: str, version: str) -> str | None:
    """The body under ``## [version]`` up to the next version heading, or None."""
    version = version.removeprefix("v")
    headings = list(_HEADING.finditer(text))
    for i, heading in enumerate(headings):
        if heading.group("version") != version:
            continue
        line_end = text.find("\n", heading.end())
        start = len(text) if line_end == -1 else line_end + 1
        end = headings[i + 1].start() if i + 1 < len(headings) else len(text)
        body = text[start:end].strip()
        # Sections are sometimes closed by a horizontal rule; it is layout, not content.
        body = re.sub(r"\n*^---\s*\Z", "", body, flags=re.MULTILINE).strip()
        return body or None
    return None