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

# ==============================================================================
# MongoDB Offline Volume Backup Script (Standalone Docker)
# ==============================================================================
#
# PURPOSE:
#   Creates an offline backup of the complete mongo-volume directory.
#   The database server is stopped during the backup to ensure consistency.
#
# WHEN TO USE:
#   - For standalone Docker deployments (not Docker Swarm)
#   - 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 server is stopped 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
#   - Log file: ./mongo-backup/db-backup-standalone.log
#   - Automatic rotation: keeps newest 7 backups (configurable via KEEP env var)
#
# USAGE:
#   ./db-backup--standalone.sh
#   KEEP=10 ./db-backup--standalone.sh  # Keep 10 backups instead of 7
#
# NOTE:
#   The MongoDB container will be stopped and restarted automatically.
#   Expect brief downtime during the backup process.
#
# ==============================================================================

# Configuration
SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
BACKUP_DIR="${BACKUP_DIR:-$SCRIPT_DIR/mongo-backup}"

LOG_FILE="$BACKUP_DIR/db-backup-standalone.log"
MONGO_SERVICE="mongo"
COMPOSE_FILE="$SCRIPT_DIR/docker-compose-standalone.yaml"

# Initialize log file (overwrite if exists)
mkdir -p "$(dirname "$LOG_FILE")"
> "$LOG_FILE"

# Function to log messages
log() {
  local timestamp=$(date '+%Y-%m-%d %H:%M:%S')
  echo "[$timestamp] $*" | tee -a "$LOG_FILE"
}

# stop mongo container while we copy its volume
log "Stopping MongoDB container..."
docker compose -f "$COMPOSE_FILE" stop "$MONGO_SERVICE"

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

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

mkdir -p "$BACKUP_DIR"

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

log "Creating backup: $BACKUP_FILE"
sudo tar -czvpf "$BACKUP_FILE" mongo-volume

log "Backup created successfully."

# rotate old backups: keep only the newest $KEEP files
if [ "$KEEP" -gt 0 ]; then
  log "Rotating backups, keeping the newest $KEEP files."

  # 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
      log "Removing old backup: $f"
      rm -f -- "$f"
    done
  fi

  log "Rotation completed."
else
  log "Backup rotation disabled (KEEP=$KEEP)."
fi

log "Starting MongoDB container..."
docker compose -f "$COMPOSE_FILE" start "$MONGO_SERVICE"

log "Database backup process completed successfully."