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

NETPLAN_DIR="/etc/netplan"
OUT_FILE="${NETPLAN_DIR}/99-static-ip.yaml"

if [[ $EUID -ne 0 ]]; then
  echo "Please run as root: sudo $0"
  exit 1
fi

echo "Detected network interfaces (excluding lo):"
ip -o link show | awk -F': ' '{print $2}' | grep -v '^lo$' || true
echo

read -rp "Interface name (e.g., enp0s3): " IFACE
if ! ip link show "$IFACE" >/dev/null 2>&1; then
  echo "Interface '$IFACE' not found."
  exit 1
fi

read -rp "Static IP with CIDR (e.g., 192.168.1.50/24): " STATIC_CIDR
read -rp "Gateway IPv4 (e.g., 192.168.1.1): " GATEWAY4
read -rp "DNS servers (comma-separated, e.g., 1.1.1.1,8.8.8.8): " DNS_CSV
read -rp "DNS search domains (optional, comma-separated, e.g., example.com,corp.local) [enter to skip]: " SEARCH_CSV

# Basic validation (lightweight)
if [[ ! "$STATIC_CIDR" =~ ^([0-9]{1,3}\.){3}[0-9]{1,3}/[0-9]{1,2}$ ]]; then
  echo "Static IP must look like x.x.x.x/yy"
  exit 1
fi
if [[ ! "$GATEWAY4" =~ ^([0-9]{1,3}\.){3}[0-9]{1,3}$ ]]; then
  echo "Gateway must look like x.x.x.x"
  exit 1
fi

# Convert CSV -> YAML list: "1.1.1.1,8.8.8.8" -> ["1.1.1.1", "8.8.8.8"]
to_yaml_list () {
  local csv="$1"
  # trim spaces, split on commas, rejoin
  csv="$(echo "$csv" | tr -d '[:space:]')"
  IFS=',' read -r -a arr <<< "$csv"
  local out="["
  local first=1
  for item in "${arr[@]}"; do
    [[ -z "$item" ]] && continue
    if [[ $first -eq 1 ]]; then
      out="${out}\"${item}\""
      first=0
    else
      out="${out}, \"${item}\""
    fi
  done
  out="${out}]"
  echo "$out"
}

DNS_LIST="$(to_yaml_list "$DNS_CSV")"
SEARCH_LIST=""
if [[ -n "${SEARCH_CSV// /}" ]]; then
  SEARCH_LIST="$(to_yaml_list "$SEARCH_CSV")"
fi

mkdir -p "$NETPLAN_DIR"

if [[ -f "$OUT_FILE" ]]; then
  TS="$(date +%Y%m%d-%H%M%S)"
  cp -a "$OUT_FILE" "${OUT_FILE}.bak.${TS}"
  echo "Backed up existing ${OUT_FILE} -> ${OUT_FILE}.bak.${TS}"
fi

cat > "$OUT_FILE" <<EOF
# Generated by static-ip setup script on $(date -Iseconds)
network:
  version: 2
  renderer: networkd
  ethernets:
    ${IFACE}:
      dhcp4: false
      addresses:
        - ${STATIC_CIDR}
      routes:
        - to: default
          via: ${GATEWAY4}
      nameservers:
        addresses: ${DNS_LIST}
EOF

if [[ -n "$SEARCH_LIST" ]]; then
cat >> "$OUT_FILE" <<EOF
        search: ${SEARCH_LIST}
EOF
fi

chmod 600 "$OUT_FILE"

echo
echo "Wrote netplan config to: $OUT_FILE"
echo "Validating netplan..."
netplan generate

echo "Applying netplan..."
netplan apply

echo
echo "Done. Current addresses on ${IFACE}:"
ip -brief addr show dev "$IFACE" || true
echo
echo "Default route:"
ip route show default || true