#!/bin/sh -eu
#
#  extscreen - Switches an external monitor on or off, and switches the primary monitor
#
#  Copyright (c) 2020 Samuel Lidén Borell <samuel@kodafritt.se>
#
#  Permission is hereby granted, free of charge, to any person obtaining a copy
#  of this software and associated documentation files (the "Software"), to deal
#  in the Software without restriction, including without limitation the rights
#  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
#  copies of the Software, and to permit persons to whom the Software is
#  furnished to do so, subject to the following conditions:
#
#  The above copyright notice and this permission notice shall be included in
#  all copies or substantial portions of the Software.
#
#  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
#  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
#  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
#  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
#  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
#  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
#  THE SOFTWARE.
#

mode=${1:-help}

error() {
    printf '%s\n' "$2" >&2
    exit "$1"
}

list_monitors() {
    xrandr | grep -E '^[^ ]+ connected' | cut -f 1 -d ' '
}

# Uses an heuristic to find the internal monitor. Looks for LVDS, then eDP*.
# If neither is found, we use the first connected monitor.
find_internal_monitor() {
    {
        list_monitors | grep -E "^LVDS" || list_monitors | grep -E "^eDP" || list_monitors
    } | head -n 1
}

# Lists external monitors
list_connected_external_monitors() {
    xrandr | grep -E '^[^ ]+ connected' | cut -f 1 -d ' ' | grep -vxF "$internal_monitor"
}

# Lists external monitors, even disconnecteed
list_all_external_monitors() {
    xrandr | grep -E '^[^ ]+' | cut -f 1 -d ' ' | grep -vxF "$internal_monitor" | grep -vxF 'Screen'
}

set_taskbar_monitor() {
    if [ -w ~/.config/lxpanel/LXDE/panels/panel ]; then
        sed -i -r 's/  monitor=[0-9]+/  monitor='"$1"'/' ~/.config/lxpanel/LXDE/panels/panel
        killall lxpanel || true
        (cd; exec lxpanel --profile LXDE > /dev/null 2>&1; ) &
    fi
}

if [ "x${mode%2}" != "x$mode" ]; then
    external_prim=
    internal_prim=--primary
    side="${mode%2}"
else
    external_prim=--primary
    internal_prim=
    side="$mode"
fi

case "$mode" in
left|left2|right|right2)
    internal_monitor=$(find_internal_monitor) || error 3 "Could not detect any monitors."
    external_monitors=$(list_connected_external_monitors) || error 4 "Could not detect any external monitors."
    primary=$external_prim
    farthest=$internal_monitor
    args=''
    for output in $external_monitors; do
        echo "Found external output: $output${primary:+, making primary}"
        args="$args --output $output --mode 1920x1080 --$side-of $farthest $primary"
        primary=''
        farthest=$output
    done
    primary=$internal_prim
    xrandr $args
    # FIXME internal monitor could in theory come after
    if [ "$mode" = left ] || [ "$mode" = right2 ]; then
        set_taskbar_monitor 0
    else
        set_taskbar_monitor 1
    fi
    ;;
off)
    internal_monitor=$(find_internal_monitor) || error 3 "Could not detect any monitors."
    external_monitors=$(list_all_external_monitors) || error 4 "Could not detect any external monitors."
    args=''
    for output in $external_monitors; do
        echo "found external output: $output"
        args="$args --output $output --off"
    done
    xrandr --output "$internal_monitor" --primary $args
    set_taskbar_monitor 0
    ;;
help|--help)
    cat <<EOF
usage: extscreen left|right|off|help

Switches one or more external monitors on or off, and switches the primary
monitor.

Modes:
  left   Switches external monitors on. The first one listed is made
         primary, and the monitors are placed left of the current screen.
         The LXDE panel configuration, if present, is updated and lxpanel
         is restarted. It will only update the panel called "panel", which
         the default panel is called. Additional panels will not be upated.
  right  Like "left", but puts the external monitors to the right.
  left2  Like "left", but the external screen is made secondary.
  right2 Like "right", but the external screen is made secondary.
  off    Switches external monitors
  help   Shows this help text.

EOF
    ;;
*)
    error 2 "invalid mode: $mode";;
esac