#!/bin/bash
set -uo pipefail

# Turn a machine that was something else into this classroom.
#
# A room does not arrive new. It arrives as whatever it was before: the
# sway classroom, the Hyprland experiment, a machine a technician tried
# something on. The package can describe the desktop it wants perfectly
# and still lose to one leftover symlink, which is what happened: a real
# room upgraded to the Plasma appliance and came up with the old Waybar
# across the top, mako still catching notifications, and Plasma's own
# stock panel underneath.
#
# So the installation converges the machine instead of assuming it.
# Everything here is something a classroom package created, or state this
# package can identify as belonging to a classroom shell it replaces.
# Nothing removes a file Debian owns: the old bar and the old notification
# daemon stay installed and simply stop being started.
#
# Idempotent, and safe on a machine that has none of this. Run by hand at
# any time:
#
#   sudo classroom-migrate

CLASSROOM_USER=classroom
DEVICE_CONFIG=/etc/ekklesia-classroom/device.conf

# The shells this appliance replaces. There is exactly one desktop stack
# now — SDDM, KWin, plasmashell — and every one of these is a component of
# a stack that is gone.
LEGACY_UNITS=(waybar.service mako.service swayidle.service swaybg.service)
LEGACY_PROCESSES=(waybar mako classroom-dock swaybg swayidle)
LEGACY_EXEC_PATTERN='waybar|mako|classroom-dock|classroom-notifications|sway|Hyprland|start-hyprland|classroom-session'

say() {
    echo "[classroom-migrate] $1"
}

if [[ "$(id -u)" -ne 0 ]]; then
    say "must be run as root"
    exit 1
fi

home=$(getent passwd "$CLASSROOM_USER" | cut -d: -f6)
uid=$(id -u "$CLASSROOM_USER" 2>/dev/null || true)

# ---------------------------------------------------------------- units

# Stop what is running now. The upgrade happens underneath a live session,
# so the old bar is on the screen while this runs.
if [[ -n "$uid" && -d "/run/user/$uid" ]]; then
    for unit in "${LEGACY_UNITS[@]}"; do
        runuser -u "$CLASSROOM_USER" -- env "XDG_RUNTIME_DIR=/run/user/$uid" \
            systemctl --user stop "$unit" >/dev/null 2>&1 || true
    done
fi

for process in "${LEGACY_PROCESSES[@]}"; do
    if pkill -u "$CLASSROOM_USER" -x "$process" 2>/dev/null; then
        say "stopped $process"
    fi
done

# Remove the activation, wherever it was made. `systemctl --global enable`
# writes into /etc/systemd/user; a session that set XDG_CONFIG_DIRS gets
# /etc/xdg/systemd/user as well; and a unit enabled by hand as the
# classroom user lands in the home directory. The real room had it in the
# second of those, which is why guessing one location would not have been
# enough.
wants_roots=(/etc/systemd/user /etc/xdg/systemd/user /run/systemd/user)
[[ -n "$home" ]] && wants_roots+=("$home/.config/systemd/user")

for root in "${wants_roots[@]}"; do
    [[ -d "$root" ]] || continue

    for unit in "${LEGACY_UNITS[@]}"; do
        while IFS= read -r link; do
            rm -f "$link"
            say "removed activation ${link#/}"
        done < <(find "$root" -name "$unit" -path '*.wants/*' 2>/dev/null)
    done
done

# The unit files themselves, where somebody wrote them by hand. Neither
# waybar nor mako ships a systemd unit in trixie, so a file by one of
# those names belongs to the shell this package replaces — but the rule is
# checked rather than assumed: anything a Debian package owns is left
# exactly where it is.
for root in /etc/systemd/user /etc/xdg/systemd/user "${home:+$home/.config/systemd/user}"; do
    [[ -n "$root" && -d "$root" ]] || continue

    for unit in "${LEGACY_UNITS[@]}"; do
        [[ -f "$root/$unit" ]] || continue

        if dpkg -S "$root/$unit" >/dev/null 2>&1; then
            say "left $root/$unit alone: a Debian package owns it"
            continue
        fi

        rm -f "$root/$unit"
        say "removed the hand-written $root/$unit"
    done
done

# And then say no once more, at the system level, so that a unit file
# reappearing from anywhere cannot start it. A mask is a symlink to
# /dev/null in /etc/systemd/user: visible, reversible, and it removes
# nothing.
systemctl --global mask "${LEGACY_UNITS[@]}" >/dev/null 2>&1 || true

# And the other way the old notification daemon starts: D-Bus activation.
# The package shadows mako's service file so that activation fails, but a
# session bus that is already running read its service directories at
# startup and has not seen it. Measured during crash recovery on a
# migrated machine: the panel was killed, a notification was sent while
# nothing owned the name, and mako took it.
if [[ -n "$uid" && -S "/run/user/$uid/bus" ]]; then
    runuser -u "$CLASSROOM_USER" -- env \
        "XDG_RUNTIME_DIR=/run/user/$uid" \
        "DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/$uid/bus" \
        dbus-send --session --dest=org.freedesktop.DBus --type=method_call \
        /org/freedesktop/DBus org.freedesktop.DBus.ReloadConfig \
        >/dev/null 2>&1 || true
fi

# ------------------------------------------------------------- autostart

# XDG autostart entries that start a component of the old shell. Matched on
# what they run, not on their filename, and only in the classroom's own
# directory.
if [[ -n "$home" && -d "$home/.config/autostart" ]]; then
    for entry in "$home/.config/autostart"/*.desktop; do
        [[ -e "$entry" ]] || continue

        if grep -qE "^Exec=.*($LEGACY_EXEC_PATTERN)" "$entry" 2>/dev/null; then
            rm -f "$entry"
            say "removed autostart entry $(basename "$entry")"
        fi
    done
fi

# ------------------------------------------------------------ tty1 login

# The sway classroom started its session from the login shell of an
# autologin getty. SDDM owns the session now, and two things owning tty1
# is how a machine ends up with no usable screen at all.
if [[ -n "$home" && -f "$home/.bash_profile" ]]; then
    if grep -qE "exec .*($LEGACY_EXEC_PATTERN)" "$home/.bash_profile" 2>/dev/null; then
        rm -f "$home/.bash_profile"
        say "removed the login shell that used to start the old session"
    fi
fi

rm -f /etc/systemd/system/getty@tty1.service.d/autologin.conf
rmdir --ignore-fail-on-non-empty \
    /etc/systemd/system/getty@tty1.service.d 2>/dev/null || true

# --------------------------------------------------------- device.conf

# The room's own settings file outlives every version of this package, so
# it is edited rather than replaced: the broker password is in it.
#
# COMPOSITOR chose between sway and Hyprland. There is nothing left for it
# to choose, and a stale value is worse than none — it is an instruction
# this package cannot carry out.
#
# CHANNEL decides which manifest the updater fetches. A machine left on the
# hyprland channel would be handed the Hyprland experiment again by the
# next release published there, undoing the upgrade it just took.
if [[ -f "$DEVICE_CONFIG" ]]; then
    python3 - "$DEVICE_CONFIG" <<'PY'
import re
import sys

OBSOLETE_KEYS = ("COMPOSITOR", "HYPR_APPEARANCE")
# Channels that served a desktop this package replaces.
OBSOLETE_CHANNELS = {"hyprland"}
CHANNEL = "classroom-v2"

path = sys.argv[1]

with open(path, "r", encoding="utf-8") as handle:
    lines = handle.readlines()

out = []
changed = []

for line in lines:
    key = line.split("=", 1)[0].strip() if "=" in line else ""

    if key in OBSOLETE_KEYS:
        changed.append(f"dropped {key}")
        continue

    if key == "CHANNEL":
        value = line.split("=", 1)[1].strip()

        if value.lower() in OBSOLETE_CHANNELS:
            changed.append(f"moved off the {value} channel onto {CHANNEL}")
            line = f"CHANNEL={CHANNEL}\n"

    out.append(line)

if changed:
    with open(path, "w", encoding="utf-8") as handle:
        handle.writelines(out)

    for note in changed:
        print(f"[classroom-migrate] device.conf: {note}")
PY
fi

# ------------------------------------------------------- the old session

# Plasma reads the classroom's settings out of a directory that has to be
# in XDG_CONFIG_DIRS, and the environment.d file that used to put it there
# never reached a session started by SDDM. The session script that does is
# installed by the package; this only checks it arrived, because a room
# without it is a room with no lockdown and no panel of ours.
if [[ ! -r /etc/xdg/plasma-workspace/env/zz-ekklesia-classroom.sh ]]; then
    say "WARNING: the session environment script is missing;"
    say "         the desktop will come up as stock Plasma"
fi

say "done"