#!/usr/bin/bash
#
# sync-zones.sh — rsync-based zone replication from primary to secondary
#
# Runs on the SECONDARY (netinfra-02). Syncs the zones/ directory from the
# primary (netinfra-01) every 60 seconds. When a zone file changes, Technitium
# detects the modification and reloads automatically.
#
# This is used instead of AXFR-based zone transfer because Technitium's zone
# transfer mechanism uses port 53 (standard DNS), but on the netinfra hosts
# port 53 is Pi-hole and Technitium is on port 5300. rsync-based replication
# avoids the port conflict entirely.
#
# Install as a systemd service/timer or run via cron:
#   * * * * * /home/localuser/services/technitium/sync-zones.sh
#
set -uo pipefail

PRIMARY_HOST="${PRIMARY_HOST:-pfv-netinfra-01.knel.net}"
CONFIG_DIR="${CONFIG_DIR:-/home/localuser/services/technitium/config}"
ZONE_DIR="$CONFIG_DIR/zones"
LOCK_FILE="/tmp/technitium-zone-sync.lock"
LOG_FILE="${LOG_FILE:-/home/localuser/services/technitium/sync.log}"

log() { printf '[%s] %s\n' "$(date +%H:%M:%S)" "$*" >> "$LOG_FILE"; }

# Prevent overlapping runs
exec 9>"$LOCK_FILE" || exit 0
flock -n 9 || { log "another sync is running; skipping"; exit 0; }

mkdir -p "$ZONE_DIR"

# rsync zones from primary. Use --temp-dir to avoid partial writes being
# picked up by Technitium, and --delete to remove zones deleted on primary.
log "Syncing zones from $PRIMARY_HOST..."
if rsync -az --delete --temp-dir=/tmp \
   "${PRIMARY_HOST}:$ZONE_DIR/" "$ZONE_DIR/" >> "$LOG_FILE" 2>&1; then
  zone_count=$(ls "$ZONE_DIR" | wc -l)
  log "Sync complete: $zone_count zones"
else
  log "ERROR: rsync failed (rc=$?)"
  exit 1
fi