#!/usr/bin/env python3
"""Prints the CHANGELOG.md section of one version (used as the release text).

  changelog_section.py 0.2.1 [CHANGELOG.md]

A section starts at a "## <version>" heading (anything may follow the version, e.g. " – changes
since 0.1.0") and ends before the next "## " heading. Exit code 1 if the version has no section.
"""
import re
import sys


def section(text, version):
    out, inside = [], False
    for line in text.splitlines():
        if line.startswith("## "):
            if inside:
                break
            inside = re.match(r"## v?" + re.escape(version) + r"(\s|$)", line) is not None
            continue
        if inside:
            out.append(line)
    return "\n".join(out).strip() if inside or out else None


def main():
    if len(sys.argv) < 2:
        sys.exit(__doc__)
    path = sys.argv[2] if len(sys.argv) > 2 else "CHANGELOG.md"
    with open(path, encoding="utf-8") as f:
        s = section(f.read(), sys.argv[1])
    if not s:
        sys.exit("no section for version %s in %s" % (sys.argv[1], path))
    print(s)


if __name__ == "__main__":
    main()