#!/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; screen -X quit'
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.${TWOPANE##*/}
SCREENRC=$TWOPANE/screenrc
cat > "$SCREENRC" <<'.'
unbindall
escape \0\0
escape ``
caption string '%t'
layout new
split
focus bottom
resize $BOT_SIZE
screen -ln -t "$BOT_TITLE" 1 bash "$TWOPANE"/bashrc
focus top
screen -ln -t "$TOP_TITLE" sh -c "$TOP_CMD"
exec :!:| socat -u UNIX-RECV:"$TWOPANE"/socket STDOUT
title 'output'
focus bottom
layout save 0
.

cat > "$TWOPANE"/bashrc <<'.'
trap "screen -X quit" EXIT
sendp()
{
        socat -u STDIN UNIX-SENDTO:"$TWOPANE"/socket
}
sendc()
{
        printf '%s' "$*" | sendp
}
send()
{
        sendc "$*"$'\n'
}
export -f send sendc sendp
eval "$BOT_CMD"
.

screen -c "$SCREENRC" -m -S "$STY" -ln