+# Locale Fallbacks
+#
+# Extends the I18n module to hold a fallbacks instance which is set to an
+# instance of I18n::Locale::Fallbacks by default but can be swapped with a
+# different implementation.
+#
+# Locale fallbacks will compute a number of fallback locales for a given locale.
+# For example:
+#
+# <pre><code>
+# I18n.fallbacks[:"es-MX"] # => [:"es-MX", :es, :en] </code></pre>
+#
+# Locale fallbacks always fall back to
+#
+# * all parent locales of a given locale (e.g. :es for :"es-MX") first,
+# * the current default locales and all of their parents second
+#
+# The default locales are set to [I18n.default_locale] by default but can be
+# set to something else.
+#
+# One can additionally add any number of additional fallback locales manually.
+# These will be added before the default locales to the fallback chain. For
+# example:
+#
+# # using the default locale as default fallback locale
+#
+# I18n.default_locale = :"en-US"
+# I18n.fallbacks = I18n::Locale::Fallbacks.new(:"de-AT" => :"de-DE")
+# I18n.fallbacks[:"de-AT"] # => [:"de-AT", :"de-DE", :de, :"en-US", :en]
+#
+# # using a custom locale as default fallback locale
+#
+# I18n.fallbacks = I18n::Locale::Fallbacks.new(:"en-GB", :"de-AT" => :de, :"de-CH" => :de)
+# I18n.fallbacks[:"de-AT"] # => [:"de-AT", :de, :"en-GB", :en]
+# I18n.fallbacks[:"de-CH"] # => [:"de-CH", :de, :"en-GB", :en]
+#
+# # mapping fallbacks to an existing instance
+#
+# # people speaking Catalan also speak Spanish as spoken in Spain
+# fallbacks = I18n.fallbacks
+# fallbacks.map(:ca => :"es-ES")
+# fallbacks[:ca] # => [:ca, :"es-ES", :es, :"en-US", :en]
+#
+# # people speaking Arabian as spoken in Palestine also speak Hebrew as spoken in Israel
+# fallbacks.map(:"ar-PS" => :"he-IL")
+# fallbacks[:"ar-PS"] # => [:"ar-PS", :ar, :"he-IL", :he, :"en-US", :en]
+# fallbacks[:"ar-EG"] # => [:"ar-EG", :ar, :"en-US", :en]
+#
+# # people speaking Sami as spoken in Finnland also speak Swedish and Finnish as spoken in Finnland
+# fallbacks.map(:sms => [:"se-FI", :"fi-FI"])
+# fallbacks[:sms] # => [:sms, :"se-FI", :se, :"fi-FI", :fi, :"en-US", :en]
+
+module I18n
+ module Locale
+ class Fallbacks < Hash
+ def initialize(*mappings)
+ @map = {}
+ map(mappings.pop) if mappings.last.is_a?(Hash)
+ self.defaults = mappings.empty? ? [I18n.default_locale.to_sym] : mappings
+ end
+
+ def defaults=(defaults)
+ @defaults = defaults.map { |default| compute(default, false) }.flatten
+ end
+ attr_reader :defaults
+
+ def [](locale)
+ raise InvalidLocale.new(locale) if locale.nil?
+ locale = locale.to_sym
+ super || store(locale, compute(locale))
+ end
+
+ def map(mappings)
+ mappings.each do |from, to|
+ from, to = from.to_sym, Array(to)
+ to.each do |_to|
+ @map[from] ||= []
+ @map[from] << _to.to_sym
+ end
+ end
+ end
+
+ protected
+
+ def compute(tags, include_defaults = true, exclude = [])
+ result = Array(tags).collect do |tag|
+ tags = I18n::Locale::Tag.tag(tag).self_and_parents.map! { |t| t.to_sym } - exclude
+ tags.each { |_tag| tags += compute(@map[_tag], false, exclude + tags) if @map[_tag] }
+ tags
+ end.flatten
+ result.push(*defaults) if include_defaults
+ result.uniq.compact
+ end
+ end
+ end
+end