1 files changed, 96 insertions, 0 deletions
diff --git a/lib/grafana/validator.rb b/lib/grafana/validator.rb
new file mode 100644
index 00000000000..760263f7ec9
--- /dev/null
+++ b/lib/grafana/validator.rb
@@ -0,0 +1,96 @@
+# frozen_string_literal: true
+
+# Performs checks on whether resources from Grafana can be handled
+# We have certain restrictions on which formats we accept.
+# Some are technical requirements, others are simplifications.
+module Grafana
+  class Validator
+    Error = Class.new(StandardError)
+
+    attr_reader :grafana_dashboard, :datasource, :panel, :query_params
+
+    UNSUPPORTED_GRAFANA_GLOBAL_VARS = %w(
+      $__interval_ms
+      $__timeFilter
+      $__name
+      $timeFilter
+      $interval
+    ).freeze
+
+    def initialize(grafana_dashboard, datasource, panel, query_params)
+      @grafana_dashboard = grafana_dashboard
+      @datasource = datasource
+      @panel = panel
+      @query_params = query_params
+    end
+
+    def validate!
+      validate_query_params!
+      validate_panel_type!
+      validate_variable_definitions!
+      validate_global_variables!
+      validate_datasource! if datasource
+    end
+
+    def valid?
+      validate!
+
+      true
+    rescue ::Grafana::Validator::Error
+      false
+    end
+
+    private
+
+    # See defaults in Banzai::Filter::InlineGrafanaMetricsFilter.
+    def validate_query_params!
+      return if [:from, :to].all? { |param| query_params.include?(param) }
+
+      raise_error 'Grafana query parameters must include from and to.'
+    end
+
+    # We may choose to support other panel types in future.
+    def validate_panel_type!
+      return if panel && panel[:type] == 'graph' && panel[:lines]
+
+      raise_error 'Panel type must be a line graph.'
+    end
+
+    # We must require variable definitions to create valid prometheus queries.
+    def validate_variable_definitions!
+      return unless grafana_dashboard[:dashboard][:templating]
+
+      return if grafana_dashboard[:dashboard][:templating][:list].all? do |variable|
+        query_params[:"var-#{variable[:name]}"].present?
+      end
+
+      raise_error 'All Grafana variables must be defined in the query parameters.'
+    end
+
+    # We may choose to support further Grafana variables in future.
+    def validate_global_variables!
+      return unless panel_contains_unsupported_vars?
+
+      raise_error "Prometheus must not include #{UNSUPPORTED_GRAFANA_GLOBAL_VARS}"
+    end
+
+    # We may choose to support additional datasources in future.
+    def validate_datasource!
+      return if datasource[:access] == 'proxy' && datasource[:type] == 'prometheus'
+
+      raise_error 'Only Prometheus datasources with proxy access in Grafana are supported.'
+    end
+
+    def panel_contains_unsupported_vars?
+      panel[:targets].any? do |target|
+        UNSUPPORTED_GRAFANA_GLOBAL_VARS.any? do |variable|
+          target[:expr].include?(variable)
+        end
+      end
+    end
+
+    def raise_error(message)
+      raise Validator::Error, message
+    end
+  end
+end