Add metric suggested name

lib/gitlab/usage/metrics/instrumentations/database_metric.rb

-# frozen_string_literal: true
+1# frozen_string_literal: true
 
 module Gitlab
   module Usage
@@ -47,6 +47,18 @@ module Gitlab
             Gitlab::Usage::Metrics::Query.for(self.class.metric_operation, relation, self.class.column)
           end
 
+          def suggested_name
+            Gitlab::Usage::Metrics::NameSuggestion.for(
+              self.class.metric_operation,
+              relation: relation,
+              column: self.class.column
+            )
+          end
+
+          def relation
+            self.class.metric_relation.call.where(time_constraints)
+          end
+
           private
 
           def relation

lib/gitlab/usage/metrics/name_suggestion.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module Usage
+    module Metrics
+      class NameSuggestion
+        FREE_TEXT_METRIC_NAME = "<please fill metric name>"
+        REDIS_EVENT_METRIC_NAME = "<please fill metric name, suggested format is: {subject}_{verb}{ing|ed}_{object} eg: users_creating_epics or merge_requests_viewed_in_single_file_mode>"
+        CONSTRAINTS_PROMPT_TEMPLATE = "<adjective describing: '%{constraints}'>"
+
+        class << self
+          def for(operation, relation: nil, column: nil)
+            case operation
+            when :count
+              name_suggestion(column: column, relation: relation, prefix: 'count')
+            when :distinct_count
+              name_suggestion(column: column, relation: relation, prefix: 'count_distinct', distinct: :distinct)
+            when :estimate_batch_distinct_count
+              name_suggestion(column: column, relation: relation, prefix: 'estimate_distinct_count')
+            when :add
+              "add_#{relation.join('_and_')}"
+            when :sum
+              name_suggestion(column: column, relation: relation, prefix: 'sum')
+            when :redis
+              REDIS_EVENT_METRIC_NAME
+            when :alt
+              FREE_TEXT_METRIC_NAME
+            else
+              raise ArgumentError, "#{operation} operation not supported"
+            end
+          end
+
+          private
+
+          def name_suggestion(relation:, column: nil, prefix: nil, distinct: nil)
+            # rubocop: disable CodeReuse/ActiveRecord
+            relation = relation.unscope(where: :created_at)
+            # rubocop: enable CodeReuse/ActiveRecord
+
+            parts = [prefix]
+            arel_column = arelize_column(relation, column)
+
+            # nil as column indicates that the counting would use fallback value of primary key.
+            # Because counting primary key from relation is the conceptual equal to counting all
+            # records from given relation, in order to keep name suggestion more condensed
+            # primary key column is skipped.
+            # eg: SELECT COUNT(id) FROM issues would translate as count_issues and not
+            # as count_id_from_issues since it does not add more information to the name suggestion
+            if arel_column != Arel::Table.new(relation.table_name)[relation.primary_key]
+              parts << arel_column.name
+              parts << 'from'
+            end
+
+            arel = arel_query(relation: relation, column: arel_column, distinct: distinct)
+            constraints = parse_constraints(relation: relation, arel: arel)
+
+            # In some cases due to performance reasons metrics are instrumented with joined relations
+            # where relation listed in FROM statement is not the one that includes counted attribute
+            # in such situations to make name suggestion more intuitive source should be inferred based
+            # on the relation that provide counted attribute
+            # EG: SELECT COUNT(deployments.environment_id) FROM clusters
+            #       JOIN deployments ON deployments.cluster_id = cluster.id
+            # should be translated into:
+            #   count_environment_id_from_deployments_with_clusters
+            # instead of
+            #   count_environment_id_from_clusters_with_deployments
+            actual_source = parse_source(relation, arel_column)
+
+            append_constraints_prompt(actual_source, [constraints], parts)
+
+            parts << actual_source
+            parts += process_joined_relations(actual_source, arel, relation, constraints)
+            parts.compact.join('_').delete('"')
+          end
+
+          def append_constraints_prompt(target, constraints, parts)
+            applicable_constraints = constraints.select { |constraint| constraint.include?(target) }
+            return unless applicable_constraints.any?
+
+            parts << CONSTRAINTS_PROMPT_TEMPLATE % { constraints: applicable_constraints.join(' AND ') }
+          end
+
+          def parse_constraints(relation:, arel:)
+            connection = relation.connection
+            ::Gitlab::Usage::Metrics::NamesSuggestions::RelationParsers::Constraints
+              .new(connection)
+              .accept(arel, collector(connection))
+              .value
+          end
+
+          # TODO: joins with `USING` keyword
+          def process_joined_relations(actual_source, arel, relation, where_constraints)
+            joins = parse_joins(connection: relation.connection, arel: arel)
+            return [] unless joins.any?
+
+            sources = [relation.table_name, *joins.map { |join| join[:source] }]
+            joins = extract_joins_targets(joins, sources)
+
+            relations = if actual_source != relation.table_name
+                          build_relations_tree(joins + [{ source: relation.table_name }], actual_source)
+                        else
+                          # in case where counter attribute comes from joined relations, the relations
+                          # diagram has to be built bottom up, thus source and target are reverted
+                          build_relations_tree(joins + [{ source: relation.table_name }], actual_source, source_key: :target, target_key: :source)
+                        end
+
+            collect_join_parts(relations: relations[actual_source], joins: joins, wheres: where_constraints)
+          end
+
+          def parse_joins(connection:, arel:)
+            ::Gitlab::Usage::Metrics::NamesSuggestions::RelationParsers::Joins
+              .new(connection)
+              .accept(arel)
+          end
+
+          def extract_joins_targets(joins, sources)
+            joins.map do |join|
+              source_regex = /(#{join[:source]})\.(\w+_)*id/i
+
+              tables_except_src = (sources - [join[:source]]).join('|')
+              target_regex = /(?<target>#{tables_except_src})\.(\w+_)*id/i
+
+              join_cond_regex = /(#{source_regex}\s+=\s+#{target_regex})|(#{target_regex}\s+=\s+#{source_regex})/i
+              matched = join_cond_regex.match(join[:constraints])
+
+              if matched
+                join[:target] = matched[:target]
+                join[:constraints].gsub!(/#{join_cond_regex}(\s+(and|or))*/i, '')
+              end
+
+              join
+            end
+          end
+
+          def build_relations_tree(joins, parent, source_key: :source, target_key: :target)
+            return [] if joins.blank?
+
+            tree = {}
+            tree[parent] = []
+
+            joins.each do |join|
+              if join[source_key] == parent
+                tree[parent] << build_relations_tree(joins - [join], join[target_key], source_key: source_key, target_key: target_key)
+              end
+            end
+            tree
+          end
+
+          def collect_join_parts(relations:, joins:, wheres:, parts: [], conjunctions: %w[with having including].cycle)
+            conjunction = conjunctions.next
+            relations.each do |subtree|
+              subtree.each do |parent, children|
+                parts << "<#{conjunction}>"
+                join_constraints = joins.find { |join| join[:source] == parent }&.dig(:constraints)
+                append_constraints_prompt(parent, [wheres, join_constraints].compact, parts)
+                parts << parent
+                collect_join_parts(relations: children, joins: joins, wheres: wheres, parts: parts, conjunctions: conjunctions)
+              end
+            end
+            parts
+          end
+
+          def arelize_column(relation, column)
+            case column
+            when Arel::Attribute
+              column
+            when NilClass
+              Arel::Table.new(relation.table_name)[relation.primary_key]
+            when String
+              if column.include?('.')
+                table, col = column.split('.')
+                Arel::Table.new(table)[col]
+              else
+                Arel::Table.new(relation.table_name)[column]
+              end
+            when Symbol
+              arelize_column(relation, column.to_s)
+            end
+          end
+
+          def parse_source(relation, column)
+            column.relation.name || relation.table_name
+          end
+
+          def collector(connection)
+            Arel::Collectors::SubstituteBinds.new(connection, Arel::Collectors::SQLString.new)
+          end
+
+          def arel_query(relation:, column: nil, distinct: nil)
+            column ||= relation.primary_key
+
+            if column.is_a?(Arel::Attribute)
+              relation.select(column.count(distinct)).arel
+            else
+              relation.select(relation.all.table[column].count(distinct)).arel
+            end
+          end
+        end
+      end
+    end
+  end
+end