#!/usr/bin/env bash
set -euo pipefail

# Libvirt context (system)
URI="qemu:///system"

# Base/template (immutable parent qcow2)
BASE="/var/lib/libvirt/images/base/debian13-template.qcow2"
TEMPLATE_DOMAIN="debian13-template"

# Lab overlays directory (dedicated)
LABDIR="/var/lib/libvirt/images/lab"

usage() {
  echo "Usage: kvm-lab-create <lab-name> [--start]"
  echo "Example: kvm-lab-create lab02 --start"
}

NAME="${1:-}"
START="${2:-}"

if [[ -z "$NAME" ]]; then
  usage
  exit 1
fi

if [[ "${START:-}" != "" && "${START:-}" != "--start" ]]; then
  usage
  exit 1
fi

DISK="${LABDIR}/${NAME}.qcow2"
XML_TMP="$(mktemp "/tmp/${NAME}.xml.XXXXXX")"

cleanup() { rm -f "$XML_TMP"; }
trap cleanup EXIT

# ---- Preconditions (read-only checks) ----
if ! sudo test -r "$BASE"; then
  echo "ERROR: Base image not readable: $BASE"
  exit 1
fi

if [[ ! -d "$LABDIR" ]]; then
  echo "ERROR: Lab directory missing: $LABDIR"
  exit 1
fi

if [[ -e "$DISK" ]]; then
  echo "ERROR: Disk already exists: $DISK"
  exit 1
fi

if virsh -c "$URI" dominfo "$NAME" &>/dev/null; then
  echo "ERROR: Domain already exists: $NAME"
  exit 1
fi

if ! virsh -c "$URI" dominfo "$TEMPLATE_DOMAIN" &>/dev/null; then
  echo "ERROR: Template domain not found in $URI: $TEMPLATE_DOMAIN"
  exit 1
fi

# ---- Create overlay disk ----
echo "Creating overlay disk: $DISK"
sudo qemu-img create -f qcow2 -F qcow2 -b "$BASE" "$DISK" >/dev/null

# Ensure qemu/libvirt can open it
sudo chown libvirt-qemu:libvirt "$DISK"
sudo chmod 0660 "$DISK"

# Quick sanity: confirm backing file is correct
echo "Validating backing file..."
sudo qemu-img info "$DISK" | grep -E "backing file:|file format:|virtual size:" || true

# ---- Clone domain XML ----
echo "Cloning domain XML from: $TEMPLATE_DOMAIN"
virsh -c "$URI" dumpxml "$TEMPLATE_DOMAIN" > "$XML_TMP"

# Replace <name> and the disk path, and force NAT-only network "default"
# Notes:
# - disk path substitution assumes template points at /var/lib/libvirt/images/base/debian13-template.qcow2
# - network replacement assumes a standard <interface type='network'> exists
sed -i \
  -e "s|<name>${TEMPLATE_DOMAIN}</name>|<name>${NAME}</name>|" \
  -e "s|${BASE}|${DISK}|g" \
  -e "s|<source network='[^']*'|<source network='default'|g" \
  "$XML_TMP"

# Extra safety: remove any hostfs passthrough (if any) to prevent host access via mounts
# (If none exist, this does nothing.)
perl -0777 -i -pe 's/<filesystem[\s\S]*?<\/filesystem>\n?//g' "$XML_TMP"
#
# Remove UUID to avoid collision with template
sed -i -E '/<uuid>[^<]*<\/uuid>/d' "$XML_TMP"
# ---- Define domain ----
echo "Defining domain: $NAME"
virsh -c "$URI" define "$XML_TMP" >/dev/null

# ---- Optional start ----
if [[ "$START" == "--start" ]]; then
  echo "Starting domain: $NAME"
  virsh -c "$URI" start "$NAME" >/dev/null
fi

echo "OK: Lab '${NAME}' created (disk: ${DISK})."
if [[ "$START" != "--start" ]]; then
  echo "To start: virsh -c $URI start ${NAME}"
fi