REFACTOR: Restoring of backups and migration of uploads to S3

lib/backup_restore/meta_data_handler.rb

@@ -0,0 +1,60 @@
+# frozen_string_literal: true
+
+module BackupRestore
+  MetaDataError = Class.new(RuntimeError)
+  MigrationRequiredError = Class.new(RuntimeError)
+
+  class MetaDataHandler
+    METADATA_FILE = "meta.json"
+
+    delegate :log, to: :@logger, private: true
+
+    def initialize(logger, filename, tmp_directory)
+      @logger = logger
+      @current_version = BackupRestore.current_version
+      @filename = filename
+      @tmp_directory = tmp_directory
+    end
+
+    def validate
+      metadata = extract_metadata
+
+      log "Validating metadata..."
+      log "  Current version: #{@current_version}"
+      log "  Restored version: #{metadata[:version]}"
+
+      if metadata[:version] > @current_version
+        raise MigrationRequiredError.new("You're trying to restore a more recent version of the schema. " \
+          "You should migrate first!")
+      end
+
+      metadata
+    end
+
+    protected
+
+    # Tries to extract the backup version from an existing
+    # metadata file (used in Discourse < v1.6) or from the filename.
+    def extract_metadata
+      metadata_path = File.join(@tmp_directory, METADATA_FILE) if @tmp_directory.present?
+
+      if metadata_path.present? && File.exists?(metadata_path)
+        metadata = load_metadata_file(metadata_path)
+      elsif @filename =~ /-#{BackupRestore::VERSION_PREFIX}(\d{14})/
+        metadata = { version: Regexp.last_match[1].to_i }
+      else
+        raise MetaDataError.new("Migration version is missing from the filename.")
+      end
+
+      metadata
+    end
+
+    def load_metadata_file(path)
+      metadata = Oj.load_file(path, symbol_keys: true)
+      raise MetaDataError.new("Failed to load metadata file.") if metadata.blank?
+      metadata
+    rescue Oj::ParseError
+      raise MetaDataError.new("Failed to parse metadata file.")
+    end
+  end
+end