#!/bin/bash
set -e
set -f
set -o pipefail
shopt -s lastpipe
PROGNAME=${0##*/}

BOT_SIZE=8
BOT_TITLE=input
BOT_CMD=sendstream
if [ $# = 0 ]
then
        TOP_CMD="$SHELL -i"
else
        TOP_CMD=$*
fi
TOP_TITLE=$TOP_CMD

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()
{
        cat > "$TWOPANE"/"${1:?$PROGNAME: Error: filename cannot be empty string}"
}
save_screenrc()
{
        save_file screenrc"${1:+.$1}"
}

save_screenrc <<'.'
# Disable keybindings.
unbindall
escape \0\0
# Disable messages.  This is needed for screen -X/-Q to work reasonably.
msgwait 0
msgminwait 0

caption string '%t'
layout new
split
focus bottom
resize $BOT_SIZE
screen -ln -t "$BOT_TITLE" 0 bash --noprofile --rcfile "$TWOPANE"/bashrc -i
source "$TWOPANE"/screenrc.startpane
layout save 0
.

save_screenrc 'startpane' <<.
focus top
screen -ln -t "\$TOP_TITLE" 1 $TOP_CMD
exec .!. sh -c 'socat UNIX-LISTEN:"\$TWOPANE"/socket STDIN,rawer!!STDOUT'
title 'output'
focus top
.

restart()
{
        while screen -p1 -Q info >/dev/null
        do
                screen -p1 -X kill
        done
        screen -X source "$TWOPANE"/screenrc.startpane
}

sendstream()
{
        socat_stty_opts=(
                rawer
                echo=0
                intr=0
                quit=0
                eof=0
                start=0
                stop=0
                susp=0
                lnext=0

                opost=1
                onlcr=1
                onlret=1
        )
        stty=$(printf %s, "${socat_stty_opts[@]}")

        trap ': SIGUSR1; restart' USR1
        exec 100<&0 101>&1
        while true
        do
                coproc SOCAT \
                {
                        socat STDIN!!STDOUT UNIX-CONNECT:"$TWOPANE"/socket,forever
                        kill -USR1 $$
                }
                exec 200<&${SOCAT[0]} 201>&${SOCAT[1]}
                socat FD:100,${stty%,}!!STDOUT STDIN!!STDOUT <&200 |
                input_filter |
                tee >(output_filter | soft_cursor >&101) >&201
                reset -I -Q -w
                exec 200<&- 201>&-
                wait -f "$SOCAT_PID" 2>/dev/null
        done
}

input_filter()
{
        while read -N1
        do
                case "$REPLY" in
                        a ) echo -n "${REPLY@U}" ;;
                        A ) echo -n "${REPLY@L}" ;;
                        * ) echo -n "$REPLY" ;;
                esac
        done
}

output_filter()
{
        cat -vt
}

soft_cursor()
{
        printf $'\033[43m \b'
        while read -N1
        do
                printf '%s' \
                        $'\033[00m \b' \
                        "$REPLY" \
                        $'\033[43m \b'
        done
}

save_file bashrc <<.
set -f
set -b
set -o pipefail
shopt -s lastpipe
trap "screen -X quit" EXIT
$(declare -f)
export PS1="\$BOT_TITLE\$ "

if [ "\$SHOW_SOCAT_ERRORS" ]
then
        exec 20>&2
else
        exec 20>/dev/null
fi

\$BOT_CMD
.

main()
{
        screen -c "$TWOPANE"/screenrc -m -S "$STY" -ln
}

main "$@"