#!/bin/bash
set -e
set -f
set -o pipefail
shopt -s lastpipe

BOT_SIZE=8
BOT_TITLE=input
BOT_CMD='PS1="$BOT_TITLE\$ " bash --noprofile --norc -i'
TOP_CMD='PS1="$TOP_TITLE\$ " bash --noprofile --norc -i'
TOP_TITLE=output

TWOPANE=$(mktemp -d)
export TWOPANE TOP_CMD BOT_CMD TOP_TITLE BOT_TITLE BOT_SIZE
trap 'rm -r "$TWOPANE"' EXIT
STY=twopane.${TWOPANE##*/}
save_file()
{
        out=$TWOPANE/${1:?$0: filename cannot be empty string}
        cat > "$out"
}
save_screenrc()
{
        save_file screenrc"${1:+.$1}"
}

save_screenrc <<'.'
unbindall
escape \0\0
caption string '%t'
layout new
split
focus bottom
resize $BOT_SIZE
screen -ln -t "$BOT_TITLE" 0 bash "$TWOPANE"/bashrc

source "$TWOPANE"/screenrc.startpane
.

save_screenrc 'startpane' <<'.'
focus top
screen -ln -t "$TOP_TITLE" 1 sh -c "$TOP_CMD; screen -X focus top; screen -X remove"
exec :!. socat -u UNIX-RECV:"$TWOPANE"/socket STDOUT
title 'output'
focus bottom
layout save 0
.

save_screenrc 'restart' <<'.'
layout new
split
focus bottom
resize $BOT_SIZE
select 0
title 'input'

source "$TWOPANE"/screenrc.startpane
.

save_file bashrc <<'.'
trap "screen -X quit" EXIT
restart()
{
        screen -X source "$TWOPANE"/screenrc.restart
}
sendp()
{
        socat -u STDIN UNIX-SENDTO:"$TWOPANE"/socket
}
sendc()
{
        printf '%s' "$*" | sendp
}
send()
{
        sendc "$*"$'\n'
}
start()
{
        while read -r -N1
        do
                sendc "$REPLY"
        done
}
export -f restart sendp sendc send start
bash -c "$BOT_CMD" || read -p "Error: process terminated with exit code $?
Press enter to quit."
.

screen -c "$TWOPANE"/screenrc -m -S "$STY" -ln