Добавил генерацию колоды и улучшил бд

app/relations/cards.rb

@@ -1,9 +1,11 @@
+# frozen_string_literal: true
+
 module ClashDeckGenerator2
   module Relations
     class Cards < DB::Relation
       schema :cards, infer: true
 
-      def meta
+      def meta_cards_scope
         where(is_meta: 1)
       end
     end

app/repos/cards_repo.rb

@@ -1,9 +1,20 @@
+# frozen_string_literal: true
+
 module ClashDeckGenerator2
   module Repos
     class CardsRepo < DB::Repo[:cards]
+      commands :create
+
       def meta_cards
-        cards.meta.to_a
+        cards.meta_cards_scope.to_a
+      end
+
+      def all_cards
+        cards.to_a
+      end
+      def all
+       cards.to_a
       end
     end
   end
-end
+end 

app/services/deck_generator.rb

@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+
+module ClashDeckGenerator2
+  module Services
+    class DeckGenerator
+      DECK_SIZE = 8
+
+      def initialize(cards_repo:)
+        @cards_repo = cards_repo
+      end
+
+      def call(only_meta: true)
+        pool = only_meta ? @cards_repo.meta_cards : @cards_repo.all_cards
+        deck = sample_unique(pool, DECK_SIZE)
+
+        {
+          cards: deck,
+          avg_elixir: average_elixir(deck)
+        }
+      end
+
+      private
+
+      def sample_unique(pool, n)
+        raise "Not enough cards in pool (need #{n}, have #{pool.size})" if pool.size < n
+
+        pool.sample(n)
+      end
+
+      def average_elixir(deck)
+        sum = deck.sum { |c| c[:elixir_cost].to_i }
+        sum.fdiv(deck.size).round(2)
+      end
+    end
+  end
+end