#!/usr/bin/env bash
# Generate release notes for a tag from .project/CHANGELOG.md
#
# Usage:
#   tools/release-notes.sh <tag>           # notes since the prior tag
#   tools/release-notes.sh <tag> --full    # full CHANGELOG (for first release)
#
# Writes to stdout. The forgejo release workflow (p2-06) shells out to this
# to populate the release body; developers can also preview before tagging:
#   git tag v0.2.0 && tools/release-notes.sh v0.2.0 | less
#
# CHANGELOG format (see .project/CHANGELOG.md):
#   `YYYY-MM-DD HH:MM <topic>: <what happened> (files=N) [ref: p0-XX]`
# Newest-at-bottom, append-only. We diff the changelog between <prior_tag>..<tag>
# and emit the added lines.

set -euo pipefail

tag="${1:-}"
mode="${2:-range}"

if [ -z "$tag" ]; then
    echo "Usage: $0 <tag> [--full]" >&2
    exit 1
fi

REPO_ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
changelog="$REPO_ROOT/.project/CHANGELOG.md"
version="${tag#v}"

if [ ! -f "$changelog" ]; then
    printf 'Release %s\n\n(no CHANGELOG.md at %s)\n' "$version" "$changelog"
    exit 0
fi

echo "# Magic Civilization $version"
echo

if [ "$mode" = "--full" ]; then
    echo "_First tagged release; full CHANGELOG below:_"
    echo
    cat "$changelog"
    exit 0
fi

# Locate the prior tag via git-describe; empty if none.
prior_tag="$(git -C "$REPO_ROOT" describe --tags --abbrev=0 "${tag}^" 2>/dev/null || true)"

if [ -z "$prior_tag" ]; then
    echo "_First tagged release; full CHANGELOG below:_"
    echo
    cat "$changelog"
    exit 0
fi

echo "_Changes since ${prior_tag}:_"
echo
# `git diff` between the two tags, filtered to added lines in the CHANGELOG,
# stripped of the leading `+` and emitted verbatim.
added="$(git -C "$REPO_ROOT" diff "${prior_tag}..${tag}" -- "$changelog" \
    | grep -E '^\+[^+]' \
    | sed 's/^\+//' \
    || true)"

if [ -z "$added" ]; then
    echo "(no new CHANGELOG entries between ${prior_tag} and ${tag})"
else
    echo "$added"
fi