#!/bin/bash

# Configuration
SOURCE_DIR="/var/www/mywebapp" # Directory to backup
BACKUP_ROOT_DIR="/mnt/backups/webapps" # Root directory where backups will be stored
RETENTION_COUNT=5                  # Number of latest backups to keep

# Derive backup directory specific to the source
APP_NAME=$(basename "$SOURCE_DIR")
BACKUP_DIR="$BACKUP_ROOT_DIR/$APP_NAME"
TIMESTAMP=$(date +%Y%m%d_%H%M%S)
BACKUP_FILENAME="${APP_NAME}_backup_$TIMESTAMP.tar.gz"
FULL_BACKUP_PATH="$BACKUP_DIR/$BACKUP_FILENAME"

# --- Pre-checks ---
if [ ! -d "$SOURCE_DIR" ]; then
  echo "Error: Source directory '$SOURCE_DIR' does not exist." >&2
  exit 1
fi

# Create backup directory if it doesn't exist
mkdir -p "$BACKUP_DIR"
if [ $? -ne 0 ]; then
  echo "Error: Failed to create backup directory '$BACKUP_DIR'. Check permissions." >&2
  exit 1
fi

echo "Starting backup of '$SOURCE_DIR' to '$FULL_BACKUP_PATH'"

# Create a gzipped tar archive of the source directory
# -C: Change to directory before adding. This ensures the archive only contains 'mywebapp', not '/var/www/mywebapp'
tar -czf "$FULL_BACKUP_PATH" -C "$(dirname "$SOURCE_DIR")" "$(basename "$SOURCE_DIR")"

if [ $? -eq 0 ]; then
  echo "Backup of '$SOURCE_DIR' created successfully at '$FULL_BACKUP_PATH'"
else
  echo "Error: Backup failed!" >&2
  rm -f "$FULL_BACKUP_PATH" # Clean up failed backup file
  exit 1
fi

# --- Optional: Enforce Retention Policy ---
echo "Enforcing retention policy: keeping last $RETENTION_COUNT backups."
# List files, sort by time (newest last), skip directories, take all but the last N, and delete
# '2>/dev/null || true' handles cases where there are less than N files
find "$BACKUP_DIR" -maxdepth 1 -name "${APP_NAME}_backup_*.tar.gz" -printf '%T@ %p
' | sort -n | cut -d' ' -f2- | head -n -"$RETENTION_COUNT" | xargs -r rm -v

echo "Backup process finished."