#!/usr/bin/env bash
set -euo pipefail

# Recursion guard: this hook calls `git commit --amend` below, which would
# trigger post-commit again. The amend invocation sets this env var inline.
[[ -n "${BASETIME_SKIP_CHANGELOG_HOOK:-}" ]] && exit 0

git_dir="$(git rev-parse --git-dir)"
if [[ -e "$git_dir/MERGE_HEAD" \
   || -e "$git_dir/CHERRY_PICK_HEAD" \
   || -e "$git_dir/REVERT_HEAD" \
   || -d "$git_dir/rebase-merge" \
   || -d "$git_dir/rebase-apply" ]]; then
  exit 0
fi

# Skip merge commits (they have a second parent).
if git rev-parse --verify -q HEAD^2 >/dev/null; then
  exit 0
fi

repo_root="$(git rev-parse --show-toplevel)"
changelog="$repo_root/CHANGELOG.md"
[[ -f "$changelog" ]] || exit 0
grep -q '^## Unreleased' "$changelog" || exit 0

# If the developer included CHANGELOG.md in the commit themselves, trust them.
if git diff-tree --no-commit-id --name-only -r HEAD | grep -qx 'CHANGELOG.md'; then
  exit 0
fi

subject="$(git log -1 --pretty=%s)"
short_sha="$(git log -1 --pretty=%h)"

case "$subject" in
  "Merge "*|"Revert "*|"fixup!"*|"squash!"*|"chore(changelog)"*|"chore(release)"*)
    exit 0
    ;;
esac

# Skip version-bump-only subjects (e.g. `0.4.9`, `v1.2.3`) so a local
# `pnpm version patch` doesn't pollute the changelog.
if [[ "$subject" =~ ^v?[0-9]+\.[0-9]+\.[0-9]+ ]]; then
  exit 0
fi

# Idempotency: if this commit's short SHA is already referenced in
# `## Unreleased`, do nothing.
if grep -qF "\`$short_sha\`" "$changelog"; then
  exit 0
fi

bullet="- ${subject}. (\`${short_sha}\`)"

python3 - "$changelog" "$bullet" <<'PY'
import re
import sys
import pathlib

path = pathlib.Path(sys.argv[1])
bullet = sys.argv[2]
text = path.read_text()


def repl(match: re.Match) -> str:
    heading = match.group(1)
    body = match.group(2).lstrip("\n")
    if body:
        return f"{heading}\n\n{bullet}\n{body}"
    return f"{heading}\n\n{bullet}\n\n"


new_text = re.sub(
    r"(^## Unreleased[^\n]*)\n+((?:.*?)(?=^## |\Z))",
    repl,
    text,
    count=1,
    flags=re.S | re.M,
)
path.write_text(new_text)
PY

git add -- "$changelog"
BASETIME_SKIP_CHANGELOG_HOOK=1 git commit --amend --no-edit --no-verify --quiet -- "$changelog"