1 files changed, 133 insertions, 0 deletions
diff --git a/lib/gitlab/usage/metrics/aggregates/aggregate.rb b/lib/gitlab/usage/metrics/aggregates/aggregate.rb
new file mode 100644
index 00000000000..72f14448656
--- /dev/null
+++ b/lib/gitlab/usage/metrics/aggregates/aggregate.rb
@@ -0,0 +1,133 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Usage
+    module Metrics
+      module Aggregates
+        UNION_OF_AGGREGATED_METRICS = 'OR'
+        INTERSECTION_OF_AGGREGATED_METRICS = 'AND'
+        ALLOWED_METRICS_AGGREGATIONS = [UNION_OF_AGGREGATED_METRICS, INTERSECTION_OF_AGGREGATED_METRICS].freeze
+        AGGREGATED_METRICS_PATH = Rails.root.join('lib/gitlab/usage_data_counters/aggregated_metrics/*.yml')
+        UnknownAggregationOperator = Class.new(StandardError)
+
+        class Aggregate
+          delegate :calculate_events_union,
+                   :weekly_time_range,
+                   :monthly_time_range,
+                   to: Gitlab::UsageDataCounters::HLLRedisCounter
+
+          def initialize
+            @aggregated_metrics = load_events(AGGREGATED_METRICS_PATH)
+          end
+
+          def monthly_data
+            aggregated_metrics_data(**monthly_time_range)
+          end
+
+          def weekly_data
+            aggregated_metrics_data(**weekly_time_range)
+          end
+
+          private
+
+          attr_accessor :aggregated_metrics
+
+          def aggregated_metrics_data(start_date:, end_date:)
+            aggregated_metrics.each_with_object({}) do |aggregation, weekly_data|
+              next if aggregation[:feature_flag] && Feature.disabled?(aggregation[:feature_flag], default_enabled: false, type: :development)
+
+              weekly_data[aggregation[:name]] = calculate_count_for_aggregation(aggregation, start_date: start_date, end_date: end_date)
+            end
+          end
+
+          def calculate_count_for_aggregation(aggregation, start_date:, end_date:)
+            case aggregation[:operator]
+            when UNION_OF_AGGREGATED_METRICS
+              calculate_events_union(event_names: aggregation[:events], start_date: start_date, end_date: end_date)
+            when INTERSECTION_OF_AGGREGATED_METRICS
+              calculate_events_intersections(event_names: aggregation[:events], start_date: start_date, end_date: end_date)
+            else
+              Gitlab::ErrorTracking
+                .track_and_raise_for_dev_exception(UnknownAggregationOperator.new("Events should be aggregated with one of operators #{ALLOWED_METRICS_AGGREGATIONS}"))
+              Gitlab::Utils::UsageData::FALLBACK
+            end
+          rescue Gitlab::UsageDataCounters::HLLRedisCounter::EventError => error
+            Gitlab::ErrorTracking.track_and_raise_for_dev_exception(error)
+            Gitlab::Utils::UsageData::FALLBACK
+          end
+
+          # calculate intersection of 'n' sets based on inclusion exclusion principle https://en.wikipedia.org/wiki/Inclusion%E2%80%93exclusion_principle
+          # this method will be extracted to dedicated module with https://gitlab.com/gitlab-org/gitlab/-/issues/273391
+          def calculate_events_intersections(event_names:, start_date:, end_date:, subset_powers_cache: Hash.new({}))
+            # calculate power of intersection of all given metrics from inclusion exclusion principle
+            # |A + B + C| = (|A| + |B| + |C|) - (|A & B| + |A & C| + .. + |C & D|) + (|A & B & C|)  =>
+            # |A & B & C| = - (|A| + |B| + |C|) + (|A & B| + |A & C| + .. + |C & D|) + |A + B + C|
+            # |A + B + C + D| = (|A| + |B| + |C| + |D|) - (|A & B| + |A & C| + .. + |C & D|) + (|A & B & C| + |B & C & D|) - |A & B & C & D| =>
+            # |A & B & C & D| = (|A| + |B| + |C| + |D|) - (|A & B| + |A & C| + .. + |C & D|) + (|A & B & C| + |B & C & D|) - |A + B + C + D|
+
+            # calculate each components of equation except for the last one |A & B & C & D| = (|A| + |B| + |C| + |D|) - (|A & B| + |A & C| + .. + |C & D|) + (|A & B & C| + |B & C & D|) -  ...
+            subset_powers_data = subsets_intersection_powers(event_names, start_date, end_date, subset_powers_cache)
+
+            # calculate last component of the equation  |A & B & C & D| = .... - |A + B + C + D|
+            power_of_union_of_all_events = begin
+              subset_powers_cache[event_names.size][event_names.join('_+_')] ||= \
+                calculate_events_union(event_names: event_names, start_date: start_date, end_date: end_date)
+            end
+
+            # in order to determine if part of equation (|A & B & C|, |A & B & C & D|), that represents the intersection that we need to calculate,
+            # is positive or negative in particular equation we need to determine if number of subsets is even or odd. Please take a look at two examples below
+            # |A + B + C| = (|A| + |B| + |C|) - (|A & B| + |A & C| + .. + |C & D|) + |A & B & C|  =>
+            # |A & B & C| = - (|A| + |B| + |C|) + (|A & B| + |A & C| + .. + |C & D|) + |A + B + C|
+            # |A + B + C + D| = (|A| + |B| + |C| + |D|) - (|A & B| + |A & C| + .. + |C & D|) + (|A & B & C| + |B & C & D|) - |A & B & C & D| =>
+            # |A & B & C & D| = (|A| + |B| + |C| + |D|) - (|A & B| + |A & C| + .. + |C & D|) + (|A & B & C| + |B & C & D|) - |A + B + C + D|
+            subset_powers_size_even = subset_powers_data.size.even?
+
+            # sum all components of equation except for the last one |A & B & C & D| = (|A| + |B| + |C| + |D|) - (|A & B| + |A & C| + .. + |C & D|) + (|A & B & C| + |B & C & D|) -  ... =>
+            sum_of_all_subset_powers = sum_subset_powers(subset_powers_data, subset_powers_size_even)
+
+            # add last component of the equation |A & B & C & D| = sum_of_all_subset_powers - |A + B + C + D|
+            sum_of_all_subset_powers + (subset_powers_size_even ? power_of_union_of_all_events : -power_of_union_of_all_events)
+          end
+
+          def sum_subset_powers(subset_powers_data, subset_powers_size_even)
+            sum_without_sign =  subset_powers_data.to_enum.with_index.sum do |value, index|
+              (index + 1).odd? ? value : -value
+            end
+
+            (subset_powers_size_even ? -1 : 1) * sum_without_sign
+          end
+
+          def subsets_intersection_powers(event_names, start_date, end_date, subset_powers_cache)
+            subset_sizes = (1..(event_names.size - 1))
+
+            subset_sizes.map do |subset_size|
+              if subset_size > 1
+                # calculate sum of powers of intersection between each subset (with given size) of metrics:  #|A + B + C + D| = ... - (|A & B| + |A & C| + .. + |C & D|)
+                event_names.combination(subset_size).sum do |events_subset|
+                  subset_powers_cache[subset_size][events_subset.join('_&_')] ||= \
+                    calculate_events_intersections(event_names: events_subset, start_date: start_date, end_date: end_date, subset_powers_cache: subset_powers_cache)
+                end
+              else
+                # calculate sum of powers of each set (metric) alone  #|A + B + C + D| = (|A| + |B| + |C| + |D|) - ...
+                event_names.sum do |event|
+                  subset_powers_cache[subset_size][event] ||= \
+                    calculate_events_union(event_names: event, start_date: start_date, end_date: end_date)
+                end
+              end
+            end
+          end
+
+          def load_events(wildcard)
+            Dir[wildcard].each_with_object([]) do |path, events|
+              events.push(*load_yaml_from_path(path))
+            end
+          end
+
+          def load_yaml_from_path(path)
+            YAML.safe_load(File.read(path))&.map(&:with_indifferent_access)
+          end
+        end
+      end
+    end
+  end
+end