app/queries/expenses/total_query.rb

@@ -0,0 +1,24 @@
+module Expenses
+  class TotalQuery
+    def call
+      ActiveRecord::Base.connection.execute(query).first
+    end
+
+    private
+
+    def query
+      <<~SQL
+        SELECT count(amount) as fixed,
+               0 as fixed_count,
+               0 as variable,
+               0 as variable_count,
+               0 as total,
+               0 as total_count,
+               0 as max_projected,
+               0 as per_person
+        FROM EXPENSES
+        LIMIT 1;
+      SQL
+    end
+  end
+end

spec/factories/expense.rb

@@ -0,0 +1,16 @@
+FactoryBot.define do
+    factory :expense do
+      sequence(:name) { |i| "Expense #{i}" }
+      pricing_type { "fixed" }
+      amount { 100 }
+    end
+
+    trait :fixed do
+      pricing_type { "fixed" }
+    end
+
+    trait :per_person do
+      pricing_type { "per_person" }
+    end
+  end
+  

spec/queries/expenses/total_query_spec.rb

@@ -0,0 +1,84 @@
+require 'rails_helper'
+
+module Expenses
+  RSpec.describe TotalQuery do
+    describe '#call' do
+      let(:response) { described_class.new.call }
+
+      before do
+        create_list(:guest, 2, status: :confirmed)
+        create_list(:guest, 3, status: :considered)
+        create_list(:guest, 4, status: :invited)
+        create_list(:guest, 5, status: :tentative)
+        create_list(:guest, 6, status: :declined)
+      end
+
+      context "when there is no expense" do
+        it "returns zero in all values", :aggregate_failures do
+          expect(response["fixed"]).to be_zero
+          expect(response["fixed_count"]).to be_zero
+          expect(response["variable"]).to be_zero
+          expect(response["variable_count"]).to be_zero
+          expect(response["total"]).to be_zero
+          expect(response["total_count"]).to be_zero
+          expect(response["max_projected"]).to be_zero
+          expect(response["per_person"]).to be_zero
+        end
+      end
+
+      context "when there are only fixed expenses" do
+        before do
+          create(:expense, :fixed, amount: 100)
+          create(:expense, :fixed, amount: 200)
+        end
+
+        it "returns the sum of fixed expenses" do
+          expect(response["fixed"]).to eq(300)
+          expect(response["fixed_count"]).to eq(2)
+          expect(response["variable"]).to be_zero
+          expect(response["variable_count"]).to be_zero
+          expect(response["total"]).to eq(300)
+          expect(response["total_count"]).to eq(2)
+          expect(response["max_projected"]).to eq(300)
+          expect(response["per_person"]).to eq(150)
+        end
+      end
+
+      context "when there are only variable expenses" do
+        before do
+          create(:expense, :per_person, amount: 100)
+          create(:expense, :per_person, amount: 200)
+        end
+
+        it "returns zero in the values and nonzero in the count", :aggregate_failures do
+          expect(response["fixed"]).to be_zero
+          expect(response["fixed_count"]).to be_zero
+          expect(response["variable"]).to eq(300)
+          expect(response["variable_count"]).to eq(2)
+          expect(response["total"]).to eq(2*300)
+          expect(response["total_count"]).to eq(2)
+          expect(response["max_projected"]).to eq(11*300)
+        end
+      end
+
+      context "when there are both fixed and variable expenses" do
+        before do
+          create(:expense, :fixed, amount: 100)
+          create(:expense, :fixed, amount: 200)
+          create(:expense, :per_person, amount: 50)
+        end
+
+        it "returns the sum of fixed and variable expenses", :aggregate_failures do
+          expect(response["fixed"]).to eq(300)
+          expect(response["fixed_count"]).to eq(2)
+          expect(response["variable"]).to eq(50)
+          expect(response["variable_count"]).to eq(1)
+          expect(response["total"]).to eq(100 + 200 + 50 * 2)
+          expect(response["total_count"]).to eq(3)
+          expect(response["max_projected"]).to eq(100 + 200 + 11*50)
+          expect(response["per_person"]).to eq(200)
+        end
+      end
+    end
+  end
+end