#!/usr/bin/env bash
#
# bf-gui-on - Switch the field terminal to graphical mode and prepare RDP.
#
# Enables and starts the display manager plus xRDP services, isolates the
# graphical target, then waits until RDP is ready to accept sessions.
# Idempotent: already-graphical systems are left untouched.
#
# Install: install -m 0755 bf-gui-on /usr/local/bin/bf-gui-on
# Usage: sudo bf-gui-on [--timeout SECS]
#
set -euo pipefail

TIMEOUT=60
DISPLAY_MANAGER=""

usage() {
    cat <<'EOF'
Usage: bf-gui-on [--timeout SECS] [--help]

Switch the device to graphical mode and wait until RDP is ready.

Options:
  --timeout SECS   Seconds to wait for RDP port 3389 (default: 60)
  --help           Show this help and exit

Behavior:
  - Enables and starts the display manager (gdm3/gdm) + xrdp + xrdp-sesman
  - Runs 'systemctl isolate graphical.target'
  - Waits until TCP/3389 accepts connections (RDP ready standby)
EOF
}

while [[ $# -gt 0 ]]; do
    case "$1" in
        --timeout) TIMEOUT="${2:?missing value for --timeout}"; shift 2 ;;
        --help|-h) usage; exit 0 ;;
        *) echo "ERROR: unknown argument: $1" >&2; usage >&2; exit 2 ;;
    esac
done

if [[ "$(id -u)" -ne 0 ]]; then
    echo "ERROR: bf-gui-on must run as root (use sudo)." >&2
    exit 1
fi

log() { echo "[bf-gui-on] $*"; }

# Detect installed display manager unit (LAB validates exact names on 26.04.1).
detect_dm() {
    local candidate
    for candidate in gdm3.service gdm.service sddm.service lightdm.service; do
        if systemctl list-unit-files --type=service 2>/dev/null | grep -q "^${candidate}"; then
            echo "${candidate%.service}"
            return 0
        fi
    done
    return 1
}

if DISPLAY_MANAGER="$(detect_dm)"; then
    log "Display manager detected: ${DISPLAY_MANAGER}"
else
    log "WARNING: no display manager unit found; proceeding with xrdp only."
fi

UNITS=()
[[ -n "${DISPLAY_MANAGER}" ]] && UNITS+=("${DISPLAY_MANAGER}")
UNITS+=(xrdp xrdp-sesman)

# Enable units that exist so GUI survives reboot while switched on.
for unit in "${UNITS[@]}"; do
    if systemctl list-unit-files --type=service 2>/dev/null | grep -q "^${unit}"; then
        systemctl enable "${unit}" >/dev/null 2>&1 || true
    else
        log "WARNING: unit ${unit} not installed; skipping."
    fi
done

CURRENT="$(systemctl get-default 2>/dev/null || echo unknown)"
log "Current default target: ${CURRENT}"

log "Isolating graphical.target ..."
systemctl isolate graphical.target

for unit in "${UNITS[@]}"; do
    if systemctl list-unit-files --type=service 2>/dev/null | grep -q "^${unit}"; then
        if ! systemctl is-active --quiet "${unit}"; then
            log "Starting ${unit} ..."
            systemctl start "${unit}" || log "WARNING: failed to start ${unit}."
        else
            log "${unit} already active."
        fi
    fi
done

# Wait for RDP standby on TCP/3389.
log "Waiting for RDP (TCP/3389) up to ${TIMEOUT}s ..."
elapsed=0
while [[ "${elapsed}" -lt "${TIMEOUT}" ]]; do
    if (exec 3<>/dev/tcp/127.0.0.1/3389) >/dev/null 2>&1; then
        exec 3>&- 2>/dev/null || true
        log "RDP is ready (graphical ON)."
        exit 0
    fi
    sleep 2
    elapsed=$((elapsed + 2))
done

echo "ERROR: RDP port 3389 did not open within ${TIMEOUT}s." >&2
echo "HINT: check 'systemctl status xrdp xrdp-sesman' and journal." >&2
exit 1