#!/usr/bin/env bash
# telcheck: Check for mail blocks with telnet
# Nathan P. <code@tchbnl.net>
# 0.1a
set -euo pipefail

TEXT_BOLD="$(tput bold)"
TEXT_UNSET="$(tput sgr0)"

VERSION='0.1a'
RELEASE='Toffee'

MAIL_HOSTS=("mx-aol.mail.gm0.yahoodns.net:AOL & Yahoo!"
            "al-ip4-mx-vip1.prodigy.net:AT&T"
            "mx1.mxge.comcast.net:Comcast"
            "gmail-smtp-in.l.google.com:Gmail (Unreliable)"
            "outlook-com.olc.protection.outlook.com:Outlook & Hotmail")

show_help() {
    cat<<EOF
Check for mail server blocks with telnet

Usage: $(basename "${0}") [OPTIONS] [ARGS]

Options:
    -b, --source [IP]   Specify the source IP to check against
    -h, --help          Show this message
    -v, --version       Show version and release
    -B, --battle        Experimental space battle simulator
EOF
}

main() {
    if [[ -v SOURCE_IP ]]; then
        ips="$(ip addr | grep inet | awk '{print $2}' | \
            awk -F '/' '{print $1}' | grep -Ev '127.0.0.1|::1')"

        if ! echo "${ips}" | grep -wq "${SOURCE_IP}"; then
            echo "${SOURCE_IP} wasn't found on this server."
            exit
        fi
    else
        SOURCE_IP="$(ip route get 1.1.1.1 | head -n 1 | awk '{print $7}')"
    fi

    echo "Checking ${SOURCE_IP}..."

    for host in "${MAIL_HOSTS[@]}"; do
        host_name="$(echo "${host}" | awk -F ':' '{print $2}')"
        host_record="$(echo "${host}" | awk -F ':' '{print $1}')"

        echo
        echo "${TEXT_BOLD}${host_name}${TEXT_UNSET}"

        run_check "${host_record}"
    done
}

run_check() {
    hostname="$(hostname)"

    {
        sleep 3s;
        echo -e "EHLO ${hostname}";
        sleep 3s;
        echo -e "MAIL FROM:<root@${hostname}>";
        sleep 3s;
        echo -e "QUIT";
    } | timeout 30s telnet -b "${SOURCE_IP}" "${@}" 25 || true
}

while [[ "${#}" -gt 0 ]]; do
    case "${1}" in
        -b|--source)
            SOURCE_IP="${2}"
            break
            ;;

        -v|--version)
            echo "${VERSION} \"${RELEASE}\""
            exit 0
            ;;

        -h|--help)
            show_help
            exit 0
            ;;

        -B|--battle)
            exit 0
            ;;

        -*)
            echo -e "Not sure what ${1} is supposed to mean" >&2
            echo
            show_help
            exit 1
            ;;

        *)
            break
            ;;
    esac
done

main