#!/usr/bin/env bash

set -euo pipefail

SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
REPO_ROOT="$(cd "${SCRIPT_DIR}/.." && pwd)"
CHANGELOG="${REPO_ROOT}/CHANGELOG.md"

TAG="${1:-}"
OUTPUT="${2:-}"

if [[ -z "${TAG}" ]]; then
  echo "usage: $0 <tag> [output-file]" >&2
  exit 1
fi

TAG="${TAG#v}"
TAG="${TAG#V}"

if [[ ! -f "${CHANGELOG}" ]]; then
  echo "error: CHANGELOG.md not found at ${CHANGELOG}" >&2
  exit 1
fi

NOTES=$(TAG="${TAG}" CHANGELOG_PATH="${CHANGELOG}" python - <<'PY'
import os
import re
import sys
from pathlib import Path

changelog_path = Path(os.environ['CHANGELOG_PATH'])
tag = os.environ['TAG']
text = changelog_path.read_text(encoding='utf-8')
pattern = re.compile(rf'^## \[{re.escape(tag)}\]\s*(?:-.*)?$', re.MULTILINE)
match = pattern.search(text)
if not match:
    sys.stderr.write(f"No changelog section found for tag {tag}.\n")
    sys.exit(1)
start = match.end()
rest = text[start:]
next_heading = re.search(r'^## \[', rest, re.MULTILINE)
section = rest[:next_heading.start()] if next_heading else rest
lines = [line.rstrip() for line in section.strip().splitlines()]
print('\n'.join(lines))
PY
)

if [[ -z "${NOTES}" ]]; then
  echo "error: no content generated for tag ${TAG}" >&2
  exit 1
fi

if [[ -n "${OUTPUT}" ]]; then
  printf '%s\n' "${NOTES}" > "${OUTPUT}"
else
  printf '%s\n' "${NOTES}"
fi