[Version] Add a util class that can be used to compare versions.

lib/motion/util/version.rb

@@ -0,0 +1,47 @@
+module Motion; module Util
+  class Version
+    include Comparable
+
+    def initialize(version)
+      @version = version.to_s
+      unless @version =~ /^[.0-9]+$/
+        raise ArgumentError, "A version may only contain periods and digits."
+      end
+    end
+
+    def to_s
+      @version
+    end
+
+    def segments
+      @segments ||= @version.split('.').map(&:to_i)
+    end
+
+    # This is pretty much vendored straight from RubyGems, except we don’t
+    # care about string segments for our purposes.
+    #
+    # https://github.com/rubygems/rubygems/blob/81d806d818baeb5dcb6398ca631d772a003d078e/lib/rubygems/version.rb
+    #
+    def <=>(other)
+      return unless Version === other
+      return 0 if @version == other.to_s
+
+      lhsegments = segments
+      rhsegments = other.segments
+
+      lhsize = lhsegments.size
+      rhsize = rhsegments.size
+      limit  = (lhsize > rhsize ? lhsize : rhsize) - 1
+
+      i = 0
+      while i <= limit
+        lhs, rhs = lhsegments[i] || 0, rhsegments[i] || 0
+        i += 1
+        next if lhs == rhs
+        return lhs <=> rhs
+      end
+
+      return 0
+    end
+  end
+end; end