Add backend support for transaction categories (#524)

* Add backend support for transaction categories

* Fix tests

* Localize default category names

* Add tests

* Remove category icon and set default color

app/models/transaction/category.rb

@@ -0,0 +1,38 @@
+class Transaction::Category < ApplicationRecord
+  has_many :transactions
+  belongs_to :family
+
+  before_update :clear_internal_category, if: :name_changed?
+
+  DEFAULT_CATEGORIES = [
+    { internal_category: "income", color: "#fd7f6f" },
+    { internal_category: "food_and_drink", color: "#7eb0d5" },
+    { internal_category: "entertainment", color: "#b2e061" },
+    { internal_category: "personal_care", color: "#bd7ebe" },
+    { internal_category: "general_services", color: "#ffb55a" },
+    { internal_category: "auto_and_transport", color: "#ffee65" },
+    { internal_category: "rent_and_utilities", color: "#beb9db" },
+    { internal_category: "home_improvement", color: "#fdcce5" }
+  ]
+
+  def self.create_default_categories(family)
+    if family.transaction_categories.size > 0
+      raise ArgumentError, "Family already has some categories"
+    end
+
+    family_id = family.id
+    categories = self::DEFAULT_CATEGORIES.map { |c| {
+      name: I18n.t("transaction.default_category.#{c[:internal_category]}"),
+      internal_category: c[:internal_category],
+      color: c[:color],
+      family_id:
+    } }
+    self.insert_all(categories)
+  end
+
+  private
+
+  def clear_internal_category
+    self.internal_category = nil
+  end
+end