#!/bin/sh

set -eu

# Print the Keep-a-Changelog section for a release tag, so CI can use it as the
# body of the Gitea release page without re-implementing CHANGELOG parsing.
#
# Run as `scripts/release-notes.sh <tag>`. A leading `v` is tolerated so both
# `v1.2.3` and `1.2.3` match the `## [1.2.3]` heading. Prints to stdout and
# exits non-zero when the tag has no section, so a release can never publish
# with an empty body.
#
# Why: development/publishing.md § Release notes are extracted from the changelog.

TAG="${1:-}"
CHANGELOG="${CHANGELOG:-CHANGELOG.md}"

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

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

# `v1.2.3` and `1.2.3` are the same release; the heading only ever uses the
# bare version.
VERSION="${TAG#v}"

awk -v version="${VERSION}" '
    # A new section ends the one we are printing (or is the one we want).
    /^## \[/ {
        if (found) exit
        heading = $0
        sub(/^## \[/, "", heading)
        sub(/\].*$/, "", heading)
        if (heading == version) found = 1
        next
    }

    # Link-reference definitions live at the bottom of the file and are never
    # part of the section body. Stopping here keeps the last release notes
    # from picking them up (there is no following heading to stop at).
    /^\[[^]]+\]:/ { exit }

    found {
        if ($0 ~ /^[[:space:]]*$/) {
            # Buffer blank lines so trailing ones at the end of the section
            # are dropped instead of leaking into the release body.
            if (started) pending = pending $0 "\n"
        } else {
            printf "%s%s\n", pending, $0
            pending = ""
            started = 1
        }
    }

    END {
        if (!found) {
            printf "Error: no CHANGELOG section for [%s].\n", version > "/dev/stderr"
            exit 1
        }
    }
' "${CHANGELOG}"