#!/bin/bash
# I, Ian Kelling, follow the GNU license recommendations at
# https://www.gnu.org/licenses/license-recommendations.en.html. They
# recommend that small programs, < 300 lines, be licensed under the
# Apache License 2.0. This file contains or is part of one or more small
# programs. If a small program grows beyond 300 lines, I plan to switch
# its license to GPL.

# Copyright 2024 Ian Kelling

# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at

#     http://www.apache.org/licenses/LICENSE-2.0

# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

# based on
# http://askubuntu.com/questions/53443/how-do-i-ignore-a-proxy-if-not-available
# altered because testing a down proxy takes like 2 seconds,
# and we would do it like 100 times in a row. so cache a failed result
# locally for 10 minutes. Also, using newer option based on man apt.conf.
#
# Once when I was testing, it seemed I needed to have it output
# DIRECT after outputing the proxy url

# note, the url we are trying to fetch is $1

# note, if there is a problem, some ways to debug:
# first,
# edit /etc/apt/apt.conf.d/02proxy
# add, remove the autodetec
# Acquire::http::proxy "http://CacheServerIp:3142";
# see the /var/log/apt-cacher-ng logs
# read
# file:///usr/share/doc/apt-cacher-ng/html/index.html

proxy_host=faiserver
proxy_port=3142
proxy_url=http://$proxy_host:$proxy_port/
f=/tmp/apt_proxy_fail
if [[ ! -w /tmp ]]; then
    echo DIRECT
    exit 0
fi
modtime=$(stat -c %Y $f 2>/dev/null ) ||:
if [[ $modtime ]] && (( $(( EPOCHSECONDS - modtime  )) < 60*10 )); then
    echo DIRECT
    exit 0
else
    rm -f $f
fi
if getent hosts $proxy_host &>/dev/null && timeout 1 nc -z $proxy_host $proxy_port &>/dev/null; then
    echo $proxy_url
else
    if [[ ! -e $f || -w $f ]]; then
        touch $f
    fi
fi