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

BOT_SIZE=8
BOT_TITLE=input
BOT_CMD=start
if [ $# = 0 ]
then
        TOP_CMD="$SHELL -i"
else
        TOP_CMD=$*
fi
TOP_TITLE="Command: $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
layout save 0
.

kill_top()
{
        while screen -p1 -Q info >/dev/null
        do
                screen -p1 -X kill
        done
}

start_top()
{
        if [ $# -gt 0 ]
        then
                TOP_CMD=$*
                TOP_TITLE="Command: $TOP_CMD"
        fi
        screen -X focus top
        screen -X screen -ln -t "$TOP_TITLE" 1 $TOP_CMD
        screen -p1 -X exec .!. sh -c 'exec socat UNIX-LISTEN:"$TWOPANE"/socket STDIN,rawer!!STDOUT'
}

restart_top()
{
        kill_top
        start_top $*
}

socat_connect()
{
        socat STDIN!!STDOUT UNIX-CONNECT:"$TWOPANE"/socket,forever
        kill -USR1 $$
        [ "$TOP_EXIT" != restart ] || restart_top
}

connect()
{
        case $# in
                2 ) declare -n std0="$1" std1="$2"; local pid ;;
                3 ) declare -n pid="$1" std0="$2" std1="$3" ;;
                0 ) local std0 std1 pid ;;
                * ) exit 1 ;;
        esac
        std0=${3:-200}
        std1=${4:-201}
        disconnect $std0 $std1
        coproc SOCAT { socat_connect; }
        pid=${SOCAT_PID}
        eval "exec ${std0}<&${SOCAT[0]} ${std1}>&${SOCAT[1]}"
}

sendc()
{
        [ "${SOCAT[0]}" || connect stdin stdout
        printf '%s' "$*" >&$stdout
}

send()
{
        [ "${SOCAT[0]}" || connect stdin stdout
        printf '%s\n' "$*" >&$stdout
}

disconnect()
{
        eval "exec ${1:-200}<&- ${2:-201}>&-"
        wait -f "$SOCAT_PID" 2>/dev/null
}

restart()
{
        start
}

start()
{
        if [ "$STARTED" ]
        then
                kill_top
        else
                STARTED=y
        fi
        start_top $*
        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 ; SOCAT=() ; ' USR1
        exec 100<&0 101>&1
        while true
        do
                connect stdin stdout
                socat FD:100,${stty%,}!!STDOUT STDIN!!STDOUT <&$stdin |
                tee >(output_filter | soft_cursor >&101) >&$stdout

                reset -I -Q -w
                disconnect

                case "$TOP_EXIT" in
                        restart )
                                continue ;;
                        quit )
                                exit ;;
                        * )
                                screen -X focus bottom
                                echo
                                break
                        ;;
                esac
        done
}

quit()
{
        screen -X quit
}

focus()
{
        screen -X focus "$@"
}

output_filter()
{
        exec 15> >(exec cat -v)
        while read -r -N1
        do
                case "$REPLY" in
                        $'\n' )
                        echo -n '^J'
                        continue
                        ;;
                esac
                if [[ "$REPLY" =~ [[:print:]] ]]
                then
                        printf '%s' "$REPLY"
                else
                        printf '%s' "$REPLY" >&15
                fi
        done
}

soft_cursor()
{
        cursor=$'\033['${cursor_color:=104}$'m \b\033[00m'
        printf '%s' "$cursor"
        while read -r -N1
        do
                case "$REPLY" in
                        $'\r' ) printf '%s' "$REPLY" "$cursor" ;;
                        * ) printf '%s' $' \b' "$REPLY" "$cursor" ;;
                esac
        done
}

our_bashrc_main()
{
        set -f
        set -o pipefail
        shopt -s lastpipe
        trap "screen -X quit" EXIT
        export PS1="$BOT_TITLE\\\$ "
}

save_file bashrc <<.
${TOP_CMD@A}
${BOT_CMD@A}
${TOP_TITLE@A}
${BOT_TITLE@A}
$(declare -f)
our_bashrc_main
\$BOT_CMD
.

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

main "$@"