feat: add nominal apc

app/models/monetary_data.rb

@@ -0,0 +1,37 @@
+class MonetaryData
+  VALID_INDICATORS = %w(nominal_apc).freeze
+  INITIAL_SUPPLY = 33.6
+  SECONDARY_SUPPLY_PER_YEAR = 1.344
+
+  def id
+    Time.current.to_i
+  end
+
+  def nominal_apc
+    initial_supply = 33.6
+    secondary_supply_per_year = 1.344
+    total_supplies_per_year.each_with_index.map do |_, index|
+      cumulative_total_supply = index.zero? ? 0 : (0..index).reduce(0) { |memo, value| memo + total_supplies_per_year[value] }
+      total_supply_so_far = initial_supply + cumulative_total_supply
+      (secondary_supply_per_year / total_supply_so_far * 100).truncate(2)
+    end
+  end
+
+  private
+
+  def total_supplies_per_year
+    @total_supplies_per_year ||=
+      begin
+        max_year = 20
+        secondary_supply_per_month = SECONDARY_SUPPLY_PER_YEAR / 12
+        total_supplies_per_year =
+          (0...max_year).map do |year|
+            primary_supply_per_year = 4.2/(2**(year / 4))
+            primary_supply_per_month = primary_supply_per_year / 12
+            [primary_supply_per_month + secondary_supply_per_month] * 12
+          end
+
+        total_supplies_per_year.flatten
+      end
+  end
+end