#!/bin/bash
set -euo pipefail

# Make the desktop come from the package, every time.
#
# Plasma builds the panel from the classroom's layout script whenever it
# starts with no panel configuration, and keeps whatever it built after
# that. That means an update could change the bar in the package and
# never change it in a room — which is exactly what happened with an icon
# that outlived the file it came from.
#
# So the configuration is removed before the shell starts and the bar is
# rebuilt from the layout at every login. The desktop becomes stateless:
# there is nothing in a teacher's home that an update cannot reach, and a
# panel damaged somehow is repaired by the next login rather than by a
# technician.
#
# Nothing is lost by this. The panel is immutable to teachers by Kiosk
# policy, so there is never anything of theirs in that file.
#
# This runs before plasmashell, as a user service ordered Before it.

CLASSROOM_XDG=/etc/ekklesia-classroom/xdg
CONFIG_HOME="${XDG_CONFIG_HOME:-$HOME/.config}"
CACHE_HOME="${XDG_CACHE_HOME:-$HOME/.cache}"

say() {
    echo "classroom-desktop-reset: $1"
}

# THE CASCADE.
#
# Everything below this line is pointless if Plasma is not reading the
# classroom's settings directory at all: without it the room gets stock
# Plasma, no Kiosk restrictions and a lock screen. The session environment
# is set by /etc/xdg/plasma-workspace/env/zz-ekklesia-classroom.sh, which
# is the mechanism Plasma itself provides. This is the assertion, not the
# mechanism: if the variable arrives here wrong, say so out loud and fix it
# for the shell that is about to start rather than build a wrong desktop
# quietly.
case ":${XDG_CONFIG_DIRS:-}:" in
    *:"$CLASSROOM_XDG":*)
        ;;
    *)
        say "XDG_CONFIG_DIRS did not contain $CLASSROOM_XDG — repairing it"
        export XDG_CONFIG_DIRS="$CLASSROOM_XDG:${XDG_CONFIG_DIRS:-/etc/xdg}"
        systemctl --user set-environment \
            "XDG_CONFIG_DIRS=$XDG_CONFIG_DIRS" 2>/dev/null || true
        ;;
esac

# FOREIGN APPEARANCE STATE.
#
# A classroom machine that has been through another desktop arrives with a
# profile that answers questions the package means to answer. Two places
# sit ahead of the classroom's own directory in KConfig's cascade:
#
#   ~/.config/kdedefaults   what the last look and feel applied wrote.
#                           Plasma also treats it as the record of which
#                           look and feel is in force: remove it and the
#                           next session applies ours again from scratch,
#                           which resets the palette to the package
#                           default. That is right for a machine arriving
#                           from another desktop and wrong for a room that
#                           chose the light theme, so whose it is decides.
#
#   ~/.config/kdeglobals    the user's own file, which beats every system
#                           directory. plasma-apply-colorscheme expands a
#                           whole palette into it, so a light Breeze scheme
#                           from a previous desktop would keep the room
#                           light no matter what the package said.
#
# The colour scheme is the one piece of appearance a room is allowed to
# choose, through classroom-theme, so an Ekklesia scheme is kept and
# anything else is removed. This is not a wipe of the home directory: two
# named pieces of appearance state, neither of them a teacher's work.

# The [General] ColorScheme of a KConfig file, or nothing.
scheme_of() {
    awk -F= '
        /^\[/ { general = ($0 == "[General]"); next }
        general && $1 == "ColorScheme" { print $2; exit }
    ' "$1" 2>/dev/null || true
}

defaults_are_ours=no

if [[ -d "$CONFIG_HOME/kdedefaults" ]]; then
    case "$(scheme_of "$CONFIG_HOME/kdedefaults/kdeglobals")" in
        Ekklesia*)
            defaults_are_ours=yes
            ;;
        *)
            rm -rf "$CONFIG_HOME/kdedefaults"
            say "removed another desktop's look and feel defaults"
            ;;
    esac
fi

if [[ -f "$CONFIG_HOME/kdeglobals" ]]; then
    scheme=$(scheme_of "$CONFIG_HOME/kdeglobals")

    case "$scheme" in
        Ekklesia*)
            say "keeping the room's colour scheme ($scheme)"
            ;;
        "")
            # No scheme named. That is what Plasma leaves behind after it
            # applies a look and feel — it writes a hash instead — so the
            # palette belongs to whichever look and feel last ran, and the
            # directory above has just said whose that was.
            if [[ "$defaults_are_ours" == yes ]]; then
                say "keeping the palette the classroom's look and feel left"
            else
                rm -f "$CONFIG_HOME/kdeglobals"
                say "removed an unnamed palette from another desktop"
            fi
            ;;
        *)
            rm -f "$CONFIG_HOME/kdeglobals"
            say "removed a foreign palette ($scheme); the package supplies one"
            ;;
    esac
fi

# The room's power behaviour is policy, not preference: never sleep, never
# dim, never lock. PowerDevil loads an idle action when it finds a group
# for it, and the merged view of this file is where such a group could
# come from, so the user's copy goes at every login. Nothing of a
# teacher's is in it — there is no settings application in this room.
if [[ -f "$CONFIG_HOME/powermanagementprofilesrc" ]]; then
    rm -f "$CONFIG_HOME/powermanagementprofilesrc"
    say "cleared the user's power settings; the package supplies them"
fi

CONFIG="$CONFIG_HOME/plasma-org.kde.plasma.desktop-appletsrc"

if [[ -e "$CONFIG" ]]; then
    rm -f "$CONFIG"
    say "panel will be rebuilt from the layout"
else
    say "no panel configuration to clear"
fi

# The icon cache remembers a name it once failed to find, which outlives
# the package that later supplies it.
rm -f "$CACHE_HOME/icon-cache.kcache" 2>/dev/null || true