fix(accumulative balance chart): Fix accumulative balance chart for a…

…ccount (#34)

Gemfile

@@ -25,7 +25,6 @@ gem "bulma-rails", "~> 0.9.2"
 gem 'slim'
 gem "font-awesome-rails"
 gem 'chartkick'
-gem 'groupdate'
 
 # Use Active Storage variant
 # gem 'image_processing', '~> 1.2'

Gemfile.lock

@@ -111,8 +111,6 @@ GEM
       railties (>= 3.2, < 7)
     globalid (0.5.2)
       activesupport (>= 5.0)
-    groupdate (6.2.1)
-      activesupport (>= 5.2)
     i18n (1.8.10)
       concurrent-ruby (~> 1.0)
     jbuilder (2.11.2)
@@ -309,7 +307,6 @@ DEPENDENCIES
   factory_bot_rails (~> 6.2)
   ffaker
   font-awesome-rails
-  groupdate
   jbuilder (~> 2.7)
   letter_opener
   listen (>= 3.0.5, < 3.2)

app/models/account.rb

@@ -33,6 +33,26 @@ def transactions
   end
 
   def accumulative_balance_data
-    transactions.group_by_day(:created_at).sum(:amount)
+    result = ActiveRecord::Base.connection.execute(balance_sql)
+    result.to_h { |transaction| [transaction['date'], transaction['sum']] }
+  end
+
+  private
+
+  def balance_sql
+    <<-SQL
+      WITH trs AS (
+        SELECT
+          id,
+          created_at::date AS date,
+          CASE WHEN to_account_id = #{id} THEN amount ELSE -amount END AS amount
+        FROM transactions
+        WHERE to_account_id = #{id} OR from_account_id = #{id}
+        ORDER BY created_at::date
+      )
+      SELECT date, SUM(amount) OVER (ORDER BY date)
+      FROM trs
+      ORDER BY date;
+    SQL
   end
 end

spec/models/account_spec.rb

@@ -6,11 +6,18 @@
   describe '#accumulative_balance_data' do
     let(:parent) { create(:account, :parent) }
     let(:child) { create(:account, :children, parent: parent) }
-    let!(:first_transaction) { create(:transaction, to_account: child, from_account: parent, amount: 100, created_at: 1.day.ago) }
-    let!(:second_transaction) { create(:transaction, to_account: child, from_account: parent, amount: 50, created_at: Time.current) }
+    let!(:first_transaction) { create(:transaction, to_account: parent, from_account: child, amount: 100.0, created_at: 2.day.ago) }
+    let!(:second_transaction) { create(:transaction, to_account: child, from_account: parent, amount: 70.0, created_at: 1.day.ago) }
+    let!(:third_transaction) { create(:transaction, to_account: parent, from_account: child, amount: 50.0, created_at: Time.current) }
 
-    it 'calculates accumulative balance data' do
-      expect(parent.accumulative_balance_data).to eq({ first_transaction.created_at.to_date => 100, second_transaction.created_at.to_date => 50 })
+    context 'with positive and negative transactions' do
+      it do
+        expect(parent.accumulative_balance_data).to eq({
+                                                         first_transaction.created_at.to_date.strftime('%Y-%m-%d') => 100.0,
+                                                         second_transaction.created_at.to_date.strftime('%Y-%m-%d') => 30.0,
+                                                         third_transaction.created_at.to_date.strftime('%Y-%m-%d') => 80.0
+                                                       })
+      end
     end
   end
 end