feat: automate changelog-backed releases

1 files changed, 158 insertions, 0 deletions

diff --git a/scripts/changelog.py b/scripts/changelog.py
new file mode 100644
index 00000000..5a87d465
--- /dev/null
+++ b/scripts/changelog.py
@@ -0,0 +1,158 @@
+#!/usr/bin/env python3
+from __future__ import annotations
+
+import argparse
+import re
+import sys
+from dataclasses import dataclass
+from datetime import date
+from pathlib import Path
+
+SECTION_RE = re.compile(r"^##\s+(?:\[(?P<bracketed>[^\]]+)\]|(?P<plain>.+?))\s*$", re.MULTILINE)
+VERSION_WITH_DATE_RE = re.compile(r"^(?P<version>.+?)\s+-\s+\d{4}-\d{2}-\d{2}$")
+
+
+@dataclass(frozen=True)
+class Section:
+    title: str
+    start: int
+    end: int
+    body_start: int
+
+
+class ChangelogError(ValueError):
+    pass
+
+
+def normalize_title(raw_title: str) -> str:
+    title = raw_title.strip()
+    match = VERSION_WITH_DATE_RE.match(title)
+    if match:
+        title = match.group("version").strip()
+    if title.startswith("[") and title.endswith("]"):
+        title = title[1:-1].strip()
+    return title
+
+
+def parse_sections(text: str) -> list[Section]:
+    matches = list(SECTION_RE.finditer(text))
+    sections: list[Section] = []
+
+    for index, match in enumerate(matches):
+        title = normalize_title(match.group("bracketed") or match.group("plain") or "")
+        end = matches[index + 1].start() if index + 1 < len(matches) else len(text)
+        body_start = match.end()
+        if body_start < len(text) and text[body_start : body_start + 1] == "\n":
+            body_start += 1
+        sections.append(Section(title=title, start=match.start(), end=end, body_start=body_start))
+
+    return sections
+
+
+def find_section(text: str, wanted_title: str) -> Section:
+    for section in parse_sections(text):
+        if section.title == wanted_title:
+            return section
+    raise ChangelogError(f"section not found: {wanted_title}")
+
+
+def extract_section_body(text: str, wanted_title: str) -> str:
+    section = find_section(text, wanted_title)
+    body = text[section.body_start : section.end].strip("\n")
+    if not body.strip():
+        raise ChangelogError(f"section is empty: {wanted_title}")
+    return body + "\n"
+
+
+def prepare_release(text: str, version: str, release_date: str) -> str:
+    unreleased = None
+    existing_version = False
+
+    for section in parse_sections(text):
+        if section.title == "Unreleased":
+            unreleased = section
+        if section.title == version:
+            existing_version = True
+
+    if existing_version:
+        raise ChangelogError(f"version already exists in changelog: {version}")
+    if unreleased is None:
+        raise ChangelogError("missing Unreleased section")
+
+    unreleased_body = text[unreleased.body_start : unreleased.end].strip("\n")
+    if not unreleased_body.strip():
+        raise ChangelogError("Unreleased section is empty")
+
+    prefix = text[: unreleased.start].rstrip("\n")
+    suffix = text[unreleased.end :].strip("\n")
+
+    rebuilt = f"## Unreleased\n\n## [{version}] - {release_date}\n\n{unreleased_body}"
+    if suffix:
+        rebuilt += f"\n\n{suffix}"
+
+    if prefix:
+        return f"{prefix}\n\n{rebuilt}\n"
+    return rebuilt + "\n"
+
+
+def load_text(path: Path) -> str:
+    try:
+        return path.read_text(encoding="utf-8")
+    except FileNotFoundError as exc:
+        raise ChangelogError(f"changelog not found: {path}") from exc
+
+
+def write_text(path: Path, text: str) -> None:
+    path.write_text(text, encoding="utf-8")
+
+
+def cmd_prepare(args: argparse.Namespace) -> int:
+    path = Path(args.path)
+    original = load_text(path)
+    updated = prepare_release(original, args.version, args.date)
+    write_text(path, updated)
+    return 0
+
+
+def cmd_extract(args: argparse.Namespace) -> int:
+    path = Path(args.path)
+    body = extract_section_body(load_text(path), args.version)
+    if args.output:
+        write_text(Path(args.output), body)
+    else:
+        sys.stdout.write(body)
+    return 0
+
+
+def build_parser() -> argparse.ArgumentParser:
+    parser = argparse.ArgumentParser(description="Prepare and extract changelog release notes")
+    subparsers = parser.add_subparsers(dest="command", required=True)
+
+    prepare = subparsers.add_parser("prepare", help="Move Unreleased into a versioned section")
+    prepare.add_argument("--path", default="CHANGELOG.md")
+    prepare.add_argument("--version", required=True)
+    prepare.add_argument("--date", default=str(date.today()))
+    prepare.set_defaults(func=cmd_prepare)
+
+    extract = subparsers.add_parser("extract", help="Extract a version section body")
+    extract.add_argument("--path", default="CHANGELOG.md")
+    extract.add_argument("--version", required=True)
+    extract.add_argument("--output")
+    extract.set_defaults(func=cmd_extract)
+
+    return parser
+
+
+def main() -> int:
+    parser = build_parser()
+    args = parser.parse_args()
+
+    try:
+        return args.func(args)
+    except ChangelogError as exc:
+        print(f"error: {exc}", file=sys.stderr)
+        return 1
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())