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require 'locale'

module HTTPHeaders
# RFC2616 Accept-Language field
# (also used in RFC2798 'preferredLanguage' LDAP attribute type)
class AcceptLanguage
LANG_RANGE_Q_PATTERN="([a-z]{1,8}(-[a-z]{1,8})*|\\*)(;q=(1|0\.\d+))?"
ACCEPT_LANG_PATTERN="#{LANG_RANGE_Q_PATTERN}([ ]*,[ ]*#{LANG_RANGE_Q_PATTERN})*"

attr_reader :sorted_language_list

def initialize(sorted_language_list)
# if no preference list, then assume that all languages are equally acceptable
@sorted_language_list = sorted_language_list.empty? ? ["*"] : sorted_language_list
end

def self.parse(accept_language_list)
return nil unless accept_language_list =~ Regexp.new(ACCEPT_LANG_PATTERN, Regexp::EXTENDED | Regexp::IGNORECASE)

list = accept_language_list.split(',').collect do |lang_range_q|
lang_range, quality = lang_range_q.split(';')
quality ||= 1
LanguageRange.new(lang_range, quality)
end

new(list.sort)
end

def reduce(available_language_list)
tag_list = available_language_list.collect do |tag|
l_tag = Locale::Tag.parse(tag).to_rfc

match = []
@sorted_language_list.each do |lr|
match << lr if lr.range == "*" or
lr.range == l_tag.to_s or
(lr.range + "-" == l_tag.to_s[0, lr.range.size + 1])
end
match.sort_by {|lr| lr.range.size }

quality = match.empty? ? 0 : match.last.quality

LanguageRange.new(l_tag, quality)
end

acceptable_tag_list = tag_list.select {|lr| lr.quality != 0 }
acceptable_tag_list.sort
end
end

class LanguageRange
include Comparable

attr_reader :quality

def initialize(lang_range, quality)
@l_lang_range = (lang_range.is_a? Locale::Tag::Simple) ? lang_range : Locale::Tag.parse(lang_range).to_rfc
@quality = quality.to_f
end

def range
@l_lang_range.to_s
end

def <=>(lr)
r = self.quality <=> lr.quality
# if quality is equal, then prefer the most specific language range
if r == 0
self.range.size <=> lr.range.size
else
r
end
end
end
end
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