s2sctl

#! /bin/sh
set -e

program='space2super'
binary="$(dirname "$0")/$program"

config_dir="${XDG_CONFIG_HOME:-$HOME/.config}/$program"
config="$config_dir/config"

default_typed_space_timeout=500
typed_space_timeout=$(
    awk '$1 == "timeout_millisec" { print $2; }' "$config" 2> /dev/null ||
        echo "$default_typed_space_timeout")

log_file="$config_dir/$program.log"
original_xmodmap="$config_dir/xmodmap.original"
xmodmap_changes="$config_dir/xmodmap.changes"

quiet=false

_log() {
    be_quiet=$quiet
    if [ "$1" = '--force' ]; then
        be_quiet=false
        shift
    fi
    if [ "$be_quiet" = false ]; then
        echo "$@" >&2
    fi
}

_die() {
    _log --force "$@"
    exit 1
}

_check_command() {
    checked_command=$1
    if ! command -v "$checked_command" > /dev/null 2>&1; then
        _die "'s2sctl' requires the '$checked_command' command to run."
    fi
}
_check_command awk
_check_command pgrep
_check_command pkill
_check_command xmodmap

_signal() {
    _signal_id=$1
    pkill --exact "-$_signal_id" "$program"
}

_print_key_code_mappings() {
    # Instructs `xmodmap` to print out the current keymap table in the form it can consume.
    xmodmap -pke || _die 'Listing key code mappings failed.'
}

_print_space_key_mappings() {
    _print_key_code_mappings | grep -w 'space' ||
        _die 'Could not find any key code mappings of the Space key.'
}

_restore_original_key_code_mappings() {
    xmodmap "$original_xmodmap" || _die 'Restoring the original key code mappings failed.'
}

is_running() {
    pgrep --uid "$USER" --exact --count "$program" > /dev/null 2>&1
}

start() {
    if is_running; then
        _log "Space2Super is already active. Use 's2sctl restart' to restart it."
        exit 0
    fi

    _log 'Starting Space2Super...'

    mkdir -p "$config_dir" || _die "Could not create Space2Super directory at '$config_dir'."

    _print_space_key_mappings > "$original_xmodmap"

    # An `xmodmap` mapping line looks like: `keycode 65 = space NoSymbol space NoSymbol space space`,
    # where values on the right indicate the `KeySym`s relevant to different modifier combinations,
    # the first indicating no modifiers.

    # Determine what the original Space key code was (most likely 65).
    original_space_key_code=$(awk '{ print $2; exit; }' "$original_xmodmap")
    if [ -z "$original_space_key_code" ]; then
        _die "Could not find any key code associated with Space (see 'xmodmap -pke')."
    fi

    # All the `xmodmap` modifications should be applied at once for performance reasons.
    {
        # Change all mentions of `space` to `Super_L`.
        awk '/keycode / {
            # Start from after the `=` sign in `$3`.
            for (field = 4; field <= NF; ++field) {
                if ($field == "space")
                    $field = "Super_L";
            };
            print;
        }' "$original_xmodmap"

        # Map an unused key code to `space` when no modifiers are applied.
        echo "keycode any = space"
    } > "$xmodmap_changes" || _die 'Could not store the generated key code mapping changes.'

    xmodmap "$xmodmap_changes" || {
        _restore_original_key_code_mappings
        _die "Applying key code mappings failed. You can check them in '$xmodmap_changes'."
    }

    # Find out what `xmodmap` has chosen for the `any` above to be able to revert it to nothing.
    # `$4` is the no-modifier `KeySym`, `$2` is the key code between `keycode` and `=`.
    _print_space_key_mappings |
        awk '$4 == "space" { print "keycode " $2 " ="; }' >> "$original_xmodmap"

    "$binary" "$original_space_key_code" "$typed_space_timeout" >> "$log_file" 2>&1 &

    _log "Space2Super is now active (log file: $log_file)."
}

stop() {
    if ! is_running; then
        _die 'Space2Super is not running.'
    fi

    _log 'Stopping Space2Super...'

    _restore_original_key_code_mappings

    if _signal TERM; then
        # Signalled. Wait a bit and check if it's done.
        sleep 0.5
        if is_running; then
            # Still alive.
            _signal KILL
            _die 'The program did not terminate gracefully, sent SIGKILL.'
        fi
    fi
}

remap() {
    is_running || return

    xmodmap "$xmodmap_changes" || {
        _restore_original_key_code_mappings
        _die "Could not re-apply the key code mappings, you can check them in '$xmodmap_changes'."
    }
}

if [ "$2" = '--quiet' ]; then
    quiet=true
fi

case "$1" in
    running)
        # Exits with a zero code if Space2Super is running, non-zero otherwise.
        is_running
        ;;
    start)
        start
        ;;
    stop)
        stop
        ;;
    restart)
        is_running && stop
        start
        ;;
    remap)
        # Use to reconfigure XKB after external changes, like `setxkbmap`.
        # Only applied if Space2Super is running.
        remap
        ;;
    *)
        _die "Usage: $0 {start|stop|restart|running|remap}"
        ;;
esac