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

# ==============================================================================
# MongoDB Offline Volume Backup Script (Docker Swarm)
# ==============================================================================
#
# PURPOSE:
#   Creates an offline backup of the complete mongo-volume directory.
#   The MongoDB service is scaled down during the backup to ensure consistency.
#
# WHEN TO USE:
#   - For Docker Swarm deployments (not standalone Docker)
#   - When you need a complete volume backup (entire MongoDB data directory)
#   - For disaster recovery scenarios
#   - When consistency is critical and downtime is acceptable
#
# BACKUP TYPE:
#   - Offline (cold) backup - DB service is scaled to 0 during backup
#   - Volume-level backup - entire mongo-volume directory
#   - Creates compressed tarball (.tar.gz) of the volume
#
# OUTPUT:
#   - Backup files stored in: ./mongo-backup/
#   - Filename format: mongo-volume-backup-YYYY-MM-DD-HH-MM.tar.gz
#   - Automatic rotation: keeps newest 7 backups (configurable via KEEP env var)
#
# USAGE:
#   ./db-backup--swarm.sh
#   KEEP=10 ./db-backup--swarm.sh  # Keep 10 backups instead of 7
#
# NOTE:
#   The MongoDB service will be scaled down to 0 and then back up to 1.
#   Expect brief downtime during the backup process.
#
# ==============================================================================

# Configuration
MONGO_SERVICE="utility-bills-tracker_mongo"

# scale down mongo service while we copy its volume
docker service scale "$MONGO_SERVICE"=0

# timestamp for filename
TIMESTAMP=$(date +"%Y-%m-%d-%H-%M")

# backup directory and retention (can be overridden via env)
BACKUP_DIR="${BACKUP_DIR:-mongo-backup}"
KEEP="${KEEP:-7}"

mkdir -p "$BACKUP_DIR"

BACKUP_FILE="$BACKUP_DIR/mongo-volume-backup-$TIMESTAMP.tar.gz"

sudo tar -czvpf "$BACKUP_FILE" mongo-volume

# rotate old backups: keep only the newest $KEEP files
if [ "$KEEP" -gt 0 ]; then
  # gather files sorted newest-first
  mapfile -t files < <(ls -1t "$BACKUP_DIR"/mongo-volume-backup-*.tar.gz 2>/dev/null || true)
  if [ "${#files[@]}" -gt "$KEEP" ]; then
    for f in "${files[@]:$KEEP}"; do
      echo "Removing old backup: $f"
      rm -f -- "$f"
    done
  fi
fi

# bring mongo service back up
docker service scale "$MONGO_SERVICE"=1