#!/usr/bin/env sh

# usage: adb-ssh-socks5 [-d]
# stupid mobile data tethering over USB
# uses adb to forward ssh ports from USB-connected android smartphone running
# sshd so as to share it's mobile data connection via socks5 proxy without
# being throttled as hotspot/tethering usage by mobile carriers

# typical setup (very fiddly and not very deterministic!):
# 1. ensure sshd is already running on port 8022 on Termux
# 2. ensure you have enabled pubkey authentication or
#    at least a plaintext password (via passwd) on Termux before starting
# 3. enable 'Developer Options > USB debugging' on android device
# 4. accept adb server's pubkey or re-accept it after 7+ days of inactivity
# 5. ensure File Transfer/MTP mode is enabled when connected over USB
# 6. just keep re-running this script if any step happens in the wrong order 🤪

# expected ports and addresses
# force IPv4
SSHD_PORT='8022'
PROXY_ADDR='127.0.0.1'
PROXY_PORT='1080'

cd $HOME

# undo changes made by by this stupid hack
if [ "$1" = '-d' ]; then
	patch -p1 -R -r - < "$0.patch"
	adb forward --remove-all
	adb kill-server
	pkill autossh
	printf '%s\n' 'Changes undone.'
	exit 0
fi

# makes this script somewhat re-entrant
patch -p1 --dry-run --forward < "$0.patch" > /dev/null 2>&1 || {
	printf '%s\n' 'Already in use, resetting environment...'
	"$0" -d
}

# forward ports from phone and open SSH session
adb start-server
printf '%s\r' 'Waiting for ADB connection over USB...'
while ! [ $(adb devices -l | wc -l) -gt 2 ]; do sleep 1; done
{	printf '%s %s\r' 'Forwarding port' "$(adb forward tcp:$SSHD_PORT tcp:$SSHD_PORT)"
}
printf '%s\r' "Ensure sshd is running on port $SSHD_PORT"
autossh -D $PROXY_PORT -p $SSHD_PORT -fnN $PROXY_ADDR

# TODO: make this more re-entrant without using flags
# don't feel like understanding iptables and tunnel devices
# just patch every config file to use socks5 proxy
sleep 1 && patch -p1 -r - < "$0.patch"