FEATURE: Support backup uploads/downloads directly to/from S3.

This reverts commit 3c59106bac4d79f39981bda3ff9db7786c1a78a0.

lib/backup_restore/backup_store.rb

@@ -0,0 +1,74 @@
+module BackupRestore
+  # @abstract
+  class BackupStore
+    class BackupFileExists < RuntimeError; end
+    class StorageError < RuntimeError; end
+
+    # @return [BackupStore]
+    def self.create(opts = {})
+      case SiteSetting.backup_location
+      when BackupLocationSiteSetting::LOCAL
+        require_dependency "backup_restore/local_backup_store"
+        BackupRestore::LocalBackupStore.new(opts)
+      when BackupLocationSiteSetting::S3
+        require_dependency "backup_restore/s3_backup_store"
+        BackupRestore::S3BackupStore.new(opts)
+      end
+    end
+
+    # @return [Array<BackupFile>]
+    def files
+      unsorted_files.sort_by { |file| -file.last_modified.to_i }
+    end
+
+    # @return [BackupFile]
+    def latest_file
+      files.first
+    end
+
+    def delete_old
+      return unless cleanup_allowed?
+      return if (backup_files = files).size <= SiteSetting.maximum_backups
+
+      backup_files[SiteSetting.maximum_backups..-1].each do |file|
+        delete_file(file.filename)
+      end
+    end
+
+    def remote?
+      fail NotImplementedError
+    end
+
+    # @return [BackupFile]
+    def file(filename, include_download_source: false)
+      fail NotImplementedError
+    end
+
+    def delete_file(filename)
+      fail NotImplementedError
+    end
+
+    def download_file(filename, destination, failure_message = nil)
+      fail NotImplementedError
+    end
+
+    def upload_file(filename, source_path, content_type)
+      fail NotImplementedError
+    end
+
+    def generate_upload_url(filename)
+      fail NotImplementedError
+    end
+
+    private
+
+    # @return [Array<BackupFile>]
+    def unsorted_files
+      fail NotImplementedError
+    end
+
+    def cleanup_allowed?
+      true
+    end
+  end
+end