chore: start adding overview page

app/controllers/dashboard/overview_controller.rb

@@ -0,0 +1,44 @@
+# frozen_string_literal: true
+
+module Dashboard
+  class OverviewController < SqmApplicationController
+    before_action :check_empty_dataset, only: [:index]
+    helper VarianceHelper
+
+    def index
+      @variance_chart_row_presenters = measures.map(&method(:presenter_for_measure))
+      @category_presenters = categories.map { |category| CategoryPresenter.new(category:) }
+      @student_response_rate_presenter = ResponseRatePresenter.new(focus: :student, school: @school,
+                                                                   academic_year: @academic_year)
+      @teacher_response_rate_presenter = ResponseRatePresenter.new(focus: :teacher, school: @school,
+                                                                   academic_year: @academic_year)
+    end
+
+    private
+
+    def presenter_for_measure(measure)
+      score = measure.score(school: @school, academic_year: @academic_year)
+
+      VarianceChartRowPresenter.new(measure:, score:)
+    end
+
+    def check_empty_dataset
+      @has_empty_dataset = subcategories.none? do |subcategory|
+        response_rate = subcategory.response_rate(school: @school, academic_year: @academic_year)
+        response_rate.meets_student_threshold? || response_rate.meets_teacher_threshold?
+      end
+    end
+
+    def measures
+      @measures ||= subcategories.flat_map(&:measures)
+    end
+
+    def subcategories
+      @subcategories ||= categories.flat_map(&:subcategories)
+    end
+
+    def categories
+      @categories ||= Category.sorted.includes(%i[measures scales admin_data_items subcategories])
+    end
+  end
+end