#!/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 rsync changes any zone file,
# Technitium is reloaded (container restart) so it serves the fresh zones —
# Technitium does NOT reliably auto-detect externally modified zone files,
# which left the secondary serving stale records (seen 2026-09-01 [#344]).
#
# 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. Native clustering tracked in [#469].
#
# 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}"
# Reload command; array form so tests can substitute a fake.
read -r -a RELOAD_CMD <<< "${RELOAD_CMD:-docker restart tsys-dns}"
export RELOAD_CMD

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

# Sync zones from the primary and reload Technitium when anything changed.
# Returns non-zero when rsync fails (reload failures are logged, not fatal).
sync_and_reload() {
  local changed rc zone_count changed_count
  # --temp-dir avoids partial writes; --delete removes zones deleted on
  # primary; --itemize-changes reports exactly what changed.
  changed=$(rsync -az --delete --itemize-changes --out-format='%n' --temp-dir=/tmp \
    "${PRIMARY_HOST}:$ZONE_DIR/" "$ZONE_DIR/" 2>> "$LOG_FILE")
  rc=$?
  if [ "$rc" -ne 0 ]; then
    return "$rc"
  fi
  zone_count=$(find "$ZONE_DIR" -maxdepth 1 -type f | wc -l)
  if [ -n "$changed" ]; then
    changed_count=$(printf '%s\n' "$changed" | wc -l)
    log "Sync complete: $zone_count zones, $changed_count changed — reloading Technitium"
    if "${RELOAD_CMD[@]}" >> "$LOG_FILE" 2>&1; then
      log "Technitium reload triggered"
    else
      log "WARN: reload command failed (rc=$?) — records may be stale until next change"
    fi
  else
    log "Sync complete: $zone_count zones (no changes)"
  fi
}

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

  mkdir -p "$ZONE_DIR"

  log "Syncing zones from $PRIMARY_HOST..."
  sync_and_reload || { log "ERROR: rsync failed (rc=$?)"; exit 1; }
}

# Allow sourcing (unit tests) without executing the sync
if [[ "${BASH_SOURCE[0]}" == "$0" ]]; then
  main
fi