1 files changed, 81 insertions, 0 deletions
diff --git a/lib/generators/gitlab/usage_metric_generator.rb b/lib/generators/gitlab/usage_metric_generator.rb
new file mode 100644
index 00000000000..c0fdcf21f20
--- /dev/null
+++ b/lib/generators/gitlab/usage_metric_generator.rb
@@ -0,0 +1,81 @@
+# frozen_string_literal: true
+
+require 'rails/generators'
+
+module Gitlab
+  class UsageMetricGenerator < Rails::Generators::Base
+    CE_DIR = 'lib/gitlab/usage/metrics/instrumentations'
+    EE_DIR = 'ee/lib/ee/gitlab/usage/metrics/instrumentations'
+    SPEC_CE_DIR = 'spec/lib/gitlab/usage/metrics/instrumentations'
+    SPEC_EE_DIR = 'ee/spec/lib/ee/gitlab/usage/metrics/instrumentations'
+
+    ALLOWED_SUPERCLASSES = {
+      generic: 'Generic',
+      database: 'Database',
+      redis: 'Redis'
+    }.freeze
+
+    ALLOWED_OPERATIONS = %w(count distinct_count estimate_batch_distinct_count).freeze
+
+    source_root File.expand_path('usage_metric/templates', __dir__)
+
+    class_option :ee, type: :boolean, optional: true, default: false, desc: 'Indicates if instrumentation is for EE'
+    class_option :type, type: :string, desc: "Metric type, must be one of: #{ALLOWED_SUPERCLASSES.keys.join(', ')}"
+    class_option :operation, type: :string, desc: "Metric operation, must be one of: #{ALLOWED_OPERATIONS.join(', ')}"
+
+    argument :class_name, type: :string, desc: 'Instrumentation class name, e.g.: CountIssues'
+
+    def create_class_files
+      validate!
+
+      template "database_instrumentation_class.rb.template", file_path if type == 'database'
+      template "generic_instrumentation_class.rb.template", file_path if type == 'generic'
+
+      template "instrumentation_class_spec.rb.template", spec_file_path
+    end
+
+    private
+
+    def validate!
+      raise ArgumentError, "Type is required, valid options are #{ALLOWED_SUPERCLASSES.keys.join(', ')}" unless type.present?
+      raise ArgumentError, "Unknown type '#{type}', valid options are #{ALLOWED_SUPERCLASSES.keys.join(', ')}" if metric_superclass.nil?
+      raise ArgumentError, "Unknown operation '#{operation}' valid operations are #{ALLOWED_OPERATIONS.join(', ')}" if type == 'database' && !ALLOWED_OPERATIONS.include?(operation)
+    end
+
+    def ee?
+      options[:ee]
+    end
+
+    def type
+      options[:type]
+    end
+
+    def operation
+      options[:operation]
+    end
+
+    def file_path
+      dir = ee? ? EE_DIR : CE_DIR
+
+      File.join(dir, file_name)
+    end
+
+    def spec_file_path
+      dir = ee? ? SPEC_EE_DIR : SPEC_CE_DIR
+
+      File.join(dir, spec_file_name)
+    end
+
+    def file_name
+      "#{class_name.underscore}_metric.rb"
+    end
+
+    def spec_file_name
+      "#{class_name.underscore}_metric_spec.rb"
+    end
+
+    def metric_superclass
+      ALLOWED_SUPERCLASSES[type.to_sym]
+    end
+  end
+end