+# The Cascade module adds the ability to do cascading lookups to backends that
+# are compatible to the Simple backend.
+#
+# By cascading lookups we mean that for any key that can not be found the
+# Cascade module strips one segment off the scope part of the key and then
+# tries to look up the key in that scope.
+#
+# E.g. when a lookup for the key :"foo.bar.baz" does not yield a result then
+# the segment :bar will be stripped off the scope part :"foo.bar" and the new
+# scope :foo will be used to look up the key :baz. If that does not succeed
+# then the remaining scope segment :foo will be omitted, too, and again the
+# key :baz will be looked up (now with no scope).
+#
+# To enable a cascading lookup one passes the :cascade option:
+#
+# I18n.t(:'foo.bar.baz', :cascade => true)
+#
+# This will return the first translation found for :"foo.bar.baz", :"foo.baz"
+# or :baz in this order.
+#
+# The cascading lookup takes precedence over resolving any given defaults.
+# I.e. defaults will kick in after the cascading lookups haven't succeeded.
+#
+# This behavior is useful for libraries like ActiveRecord validations where
+# the library wants to give users a bunch of more or less fine-grained options
+# of scopes for a particular key.
+#
+# Thanks to Clemens Kofler for the initial idea and implementation! See
+# http://github.com/clemens/i18n-cascading-backend
+
+module I18n
+ module Backend
+ module Cascade
+ def lookup(locale, key, scope = [], options = {})
+ return super unless cascade = options[:cascade]
+
+ cascade = { :step => 1 } unless cascade.is_a?(Hash)
+ step = cascade[:step] || 1
+ offset = cascade[:offset] || 1
+ separator = options[:separator] || I18n.default_separator
+ skip_root = cascade.has_key?(:skip_root) ? cascade[:skip_root] : true
+
+ scope = I18n.normalize_keys(nil, key, scope, separator)
+ key = (scope.slice!(-offset, offset) || []).join(separator)
+
+ begin
+ result = super
+ return result unless result.nil?
+ scope = scope.dup
+ end while (!scope.empty? || !skip_root) && scope.slice!(-step, step)
+ end
+ end
+ end
+end