Add deposit concept

src/game/deposit.cr

@@ -0,0 +1,40 @@
+module Game
+  class Deposit
+    class Span
+      def initialize(@res : Resources::Type, @cap : Capacity)
+      end
+
+      getter res
+      getter cap
+    end
+
+    @cur : Capacity = 0
+
+    def initialize(@res : Resources::Type, @cap : Capacity)
+      @cur = @cap
+    end
+
+    def initialize(@res : Resources::Type, @cap : Capacity, @cur : Capacity)
+    end
+
+    getter res
+    getter cap
+    getter cur
+
+    def inc(span : Span)
+      check_res span.res
+      @cur = Math.min(@cap, @cur + span.cap)
+    end
+
+    def dec(span : Span)
+      check_res span.res
+      @cur = Math.max(0, @cur - span.cap)
+    end
+
+    private def check_res(other_res : Resources::Type)
+      if @res != other_res
+        raise ResourceMismatch.new
+      end
+    end
+  end
+end