#!/bin/bash

set -eu

FILENAME="$1"

function is_new_commit {
    test -z "$(head -n1 "$FILENAME")"
}

function insert_issue_key {
    local issue_key
    issue_key="$(git symbolic-ref -q HEAD | grep -o "[A-Z]\+-[0-9]\+" | head -n1 || true)"
    if [ -n "$issue_key" ]; then
        sed -i "1i${issue_key}: " "$FILENAME"
    fi
}

if is_new_commit; then
    insert_issue_key
fi