#!/bin/bash
BASH_ARGV0=twopane.bash
echo -n "$0" >/proc/$$/comm
set -e
set -f
set -o pipefail
shopt -s lastpipe

. read_chars.bash

BOT_SIZE=8
BOT_TITLE=input

if [ $# = 0 ]
then
        TOP_CMD="$SHELL -i"
        BOT_CMD=foreground
        TOP_EXIT=prompt
        #BOT_CMD=start
        #TOP_EXIT=restart
else
        TOP_CMD=$*
        BOT_CMD=start
        TOP_EXIT=quit
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=$(systemd-escape -p "$TWOPANE")
systemd_escape_path()
{
        declare -g -n path="$1" result="$2"
        result=$(realpath "$path")
        result=${result//-/--}
        result=${result//\//-}
}
systemd_escape_path TWOPANE STY
STY=$0.$$.$STY

save_file()
{
        cat > "$TWOPANE"/"${1:?$0: 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
# Try to disable blocking the terminal on ^S.
# Doesn't seem to work here.
# More is needed.  Xterm?
nonblock on

# Enable mouse focus
defmousetrack on
mousetrack on

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
.

check_screen_pane()
{
        screen -p "$pane" -Q info >/dev/null
}

kill_screen_pane()
{
        while check_screen_pane
        do
                screen -p "$pane" -X kill
        done
}

start_screen_pane()
{
#       declare -g -a PANES
        declare -i pane="${1:-1}"
        (( pane > 0 )) || return
#       PANES+=("$pane")
        if check_screen_pane "$pane"
        then
                return
        fi
        shift
        if [ $# = 0 ]
        then
                set -f
                set -- ${TOP_CMD:-bash -i}
        fi
        TOP_TITLE="Command: ${*@Q}"
        screen -X focus top
        screen -X screen -ln -t "$TOP_TITLE" 1 "$@"
        screen -p "$pane" -X exec .!. bash -c 'exec -a top-pane-tty-forward socat UNIX-LISTEN:"$TWOPANE"/socket STDIN,cfmakeraw!!STDOUT'
}

restart_screen_pane()
{
        kill_screen_pane
        start_screen_pane "$@"
}

connect_coproc()
{
        declare -n coproc="$1"
        shift
        declare -g -n std1="${!coproc}_STDOUT"
        declare -g -n std0="${!coproc}_STDIN"
        declare -g -n opid="${!coproc}_PID"

        if [ $# = 0 ]
        then
                set -- "${!coproc}"
        fi
        if ! [ "$opid" ]
        then
                local STDERR
                {
                        coproc "${!coproc}" \
                        {
                                "$@"
                        } 2>&$STDERR {STDERR}>&-
                } {STDERR}>&2 2>/dev/null
                i "${!opid}=$opid"
                x disown
        fi
        # The copied file descriptors (unlike the original coprocess
        # file descriptors, in ${coproc[0]} and ${coproc[1]}) can be
        # passed to external processes (e.g.: socat(1) instances) and
        # used in subshells.
        {
                exec {std0}<&0 {std1}>&1
        } <&${coproc[0]} >&${coproc[1]}
}

disconnect_coproc()
{
        if [ $# = 1 ]
        then
                declare -n coproc="$1"
                declare -g -n std1="${!coproc}_STDOUT"
                declare -g -n std0="${!coproc}_STDIN"
                declare -g -n  pid="${!coproc}_PID"
                [ "$std0" -a "$std1" ] || return
                exec {std0}<&- {std1}>&-
                unset std0 std1
                x kill "$pid"
                x wait -f "$pid"
        fi
}

connect()
{
        connect_coproc SOCAT
        i "SOCAT_PID=$SOCAT_PID"
}

disconnect()
{
        i "SOCAT_STDIN=$SOCAT_STDIN SOCAT_STDOUT=$SOCAT_STDOUT SOCAT_PID=$SOCAT_PID"
        x disconnect_coproc SOCAT
}

sendc()
{
        [ "${SOCAT[0]}" ] || connect
        printf '%s' "$*" >&${SOCAT[1]}
}

send()
{
        [ "${SOCAT[0]}" ] || connect
        printf '%s\n' "$*" >&${SOCAT[1]}
}

restart()
{
        start "$@"
}

start()
{
        foreground "$@"
}

check_tty_reader()
{
        [ "$TTY_READER_PID" ] || return
        TTY_READER_JOBSPEC=$(jobs -sl | pid_to_jobspec "$TTY_READER_PID")
        [ "$TTY_READER_JOBSPEC" ]
}

pid_to_jobspec()
{
        while read jspec pid status cmd
        do
                [ "$pid" = "$1" ] || continue
                jspec=${jspec%]*}
                jspec=%${jspec#[}
                echo $jspec
                return
        done
        false
}

tty_forward()
{
        declare -i pid="$1"
        read-tty
        x kill $pid
}

SOCAT()
{
        (exec -a bottom-pane-tty-forward socat - UNIX-CONNECT:"$TWOPANE"/socket,forever)
        case "$TOP_EXIT" in
                restart )
                        start_screen_pane 1 "$@"
                ;;
                quit )
                        quit
                ;;
                prompt | * )
                ;;
        esac
        x screen -X quit
}

echosend()
{
        declare -n fd="$1"
        declare -n pid="${!fd}_PID"
        if ! [ "$fd" ]
        then
                connect_coproc SOCAT
                i "SOCAT_PID=$SOCAT_PID"
                exec {fd}> >(
                        (exec -a echosend socat - fd:${SOCAT_STDIN?e}!!-) |
                        tee >(output_filter) >&${SOCAT_STDOUT?e}
                )
                pid=$!
        fi
}

quiet_bg()
{
        local STDERR
        {
                eval "$(printf '%q ' "$@") & 2>&\$STDERR {STDERR}>&-"
        } {STDERR}>&2 2>/dev/null
}

background()
{
        start_screen_pane 1 "$@"
        focus bottom
        echosend ECHOSEND
        {
                eval "tty_forward $ECHOSEND_PID &"
        } >&$ECHOSEND
        TTY_READER_PID=$!
        printf '%s\n' \
                "#!/bin/bash" \
                "kill -TSTP $TTY_READER_PID" \
                "screen -X focus bottom" \
                > "$TWOPANE"/unforward
        chmod +x "$TWOPANE"/unforward
}

foreground()
{
        check_tty_reader || background
        focus top
        fg %tty_forward >/dev/null
        #disconnect
        focus bottom
}

foreground_loop()
{
        while true
        do
                foreground
                x kill %tty_forward 2>/dev/null
                case "$TOP_EXIT" in
                        restart )
                                x kill -INT $TTY_READER_PID $ECHOSEND_PID
                                start_screen_pane "$@"
                                continue ;;
                        quit )
                                exit ;;
                        prompt | * )
                                x kill -INT $TTY_READER_PID $ECHOSEND_PID
                                break
                        ;;
                esac
        done
}

twopane()
{
        start "$@"
}

quit()
{
        screen -X quit
}

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

output_filter()
{
        tokenize | colorize | soft_cursor
}

chr()
{
        declare -i n="$*"
        printf "\\$(printf %o "$n")"
}

colorize()
{
        while read -r
        do
                case "$REPLY" in
                        \\[0-7][0-7][0-7] ) ;;
                        * )
                                printf '%s\n' "$REPLY"
                                continue
                                ;;
                esac
                declare -i c=8#"${REPLY#?}"
                if (( c > 128 + 127 ))
                then
                        :
                elif (( c > 128 + 32 ))
                then
                        printf -v REPLY "M-$(chr c - 128)"
                elif (( c > 127 ))
                then
                        printf -v REPLY "M-^$(chr c - 128 + 64)"
                elif (( c < 32 ))
                then
                        printf -v REPLY "^$(chr c + 64)"
                fi
                printf $'\e[106m%s\e[m\n' "$REPLY"
        done
}

tokenize()
{
        while read -r -N1
        do
                if [[ "$REPLY" =~ [[:print:]] ]]
                then
                        # Output one printable character per line. It may be a
                        # multibyte unicode character.
                        printf '%s\n' "$REPLY"
                        continue
                else
                        # If it is a non-printable, then we output a
                        # multi-character line. In this case we colorize it
                        # later so that it won't be confused with multiple
                        # printable characters in the .
                        printf '\\%.3o\n' "'$REPLY"
                        continue
                fi
        done
}

soft_cursor()
{
        FMT=$'%s \b\e[%sm \e[m\b'
        REPLY=
        color=101
        while printf "$FMT" "$REPLY" "$color"
        do
                read -r || break
                let '++color <= 105' || color=101
        done
}

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

our_bashrc_main()
{
        set -m
        set -f
        set -o pipefail
        #trap 'focus bottom; resize 90%; read -p "Exit> "; quit' EXIT
        #trap 'echo USR1 >&2; focus bottom; x kill -INT %tty_forward $TTY_READER_PID $ECHOSEND_PID' USR1
        trap 'quit' USR1
        export PS1="$BOT_TITLE\\\$ "
}

save_file bashrc <<.
BASH_ARGV0=twopane
echo -n "\$0" >/proc/\$\$/comm
${TOP_CMD@A}
${BOT_CMD@A}
${TOP_TITLE@A}
${BOT_TITLE@A}

${TOP_EXIT@A}

$(declare -f)
our_bashrc_main

$BOT_CMD
.

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

main "$@"