class ActiveSupport::Inflector::Inflections

def self.instance(locale = :en)
  @__instance__[locale] ||= new
end

def self.instance_or_fallback: (Symbol locale) -> ActiveSupport::Inflector::Inflections

def self.instance_or_fallback(locale)
  I18n.fallbacks[locale].each do |k|
    return @__instance__[k] if @__instance__.key?(k)
  end
  instance(locale)
end

def acronym(word)
  @acronyms[word.downcase] = word
  define_acronym_regex_patterns
end

def clear(scope = :all)
  case scope
  when :all
    clear(:acronyms)
    clear(:plurals)
    clear(:singulars)
    clear(:uncountables)
    clear(:humans)
  when :acronyms
    @acronyms = {}
    define_acronym_regex_patterns
  when :uncountables
    @uncountables = Uncountables.new
  when :plurals, :singulars, :humans
    instance_variable_set "@#{scope}", []
  end
end

def define_acronym_regex_patterns
  @acronym_regex             = @acronyms.empty? ? /(?=a)b/ : /#{@acronyms.values.join("|")}/
  @acronyms_camelize_regex   = /^(?:#{@acronym_regex}(?=\b|[A-Z_])|\w)/
  @acronyms_underscore_regex = /(?:(?<=([A-Za-z\d]))|\b)(#{@acronym_regex})(?=\b|[^a-z])/
end

def human(rule, replacement)
  @humans.prepend([rule, replacement])
end

def initialize
  @plurals, @singulars, @uncountables, @humans, @acronyms = [], [], Uncountables.new, [], {}
  define_acronym_regex_patterns
end

def initialize_dup(orig) # :nodoc:
  %w(plurals singulars uncountables humans acronyms).each do |scope|
    instance_variable_set("@#{scope}", orig.public_send(scope).dup)
  end
  define_acronym_regex_patterns
end

def irregular(singular, plural)
  @uncountables.delete(singular)
  @uncountables.delete(plural)
  s0 = singular[0]
  srest = singular[1..-1]
  p0 = plural[0]
  prest = plural[1..-1]
  if s0.upcase == p0.upcase
    plural(/(#{s0})#{srest}$/i, '\1' + prest)
    plural(/(#{p0})#{prest}$/i, '\1' + prest)
    singular(/(#{s0})#{srest}$/i, '\1' + srest)
    singular(/(#{p0})#{prest}$/i, '\1' + srest)
  else
    plural(/#{s0.upcase}(?i)#{srest}$/,   p0.upcase   + prest)
    plural(/#{s0.downcase}(?i)#{srest}$/, p0.downcase + prest)
    plural(/#{p0.upcase}(?i)#{prest}$/,   p0.upcase   + prest)
    plural(/#{p0.downcase}(?i)#{prest}$/, p0.downcase + prest)
    singular(/#{s0.upcase}(?i)#{srest}$/,   s0.upcase   + srest)
    singular(/#{s0.downcase}(?i)#{srest}$/, s0.downcase + srest)
    singular(/#{p0.upcase}(?i)#{prest}$/,   s0.upcase   + srest)
    singular(/#{p0.downcase}(?i)#{prest}$/, s0.downcase + srest)
  end
end

def plural(rule, replacement)
  @uncountables.delete(rule) if rule.is_a?(String)
  @uncountables.delete(replacement)
  @plurals.prepend([rule, replacement])
end

def singular(rule, replacement)
  @uncountables.delete(rule) if rule.is_a?(String)
  @uncountables.delete(replacement)
  @singulars.prepend([rule, replacement])
end

def uncountable(*words)
  @uncountables.add(words)
end