class Hash

  unless defined?(Rails)
    def assert_valid_keys(*valid_keys)
      valid_keys.flatten!
      each_key do |k|
        unless valid_keys.include?(k)
          raise ArgumentError,
            "Unknown key: #{k.inspect}. Valid keys are: #{valid_keys.map(&:inspect).join(', ')}"
        end
      end
    end
  end

  unless defined?(Rails)
    def compact
      select { |k, v| !v.nil? }
    end
  end

  unless defined?(Rails)
    def compact!
      reject! { |k, v| v.nil? }
    end
  end

  unless defined?(Rails)
    def deep_merge(other_hash, &block)
      dup.deep_merge!(other_hash, &block)
    end
  end

  unless defined?(Rails)
    def deep_merge!(other_hash, &block)
      other_hash.each_pair do |current_key, other_value|
        this_value = self[current_key]

        self[current_key] = if this_value.is_a?(Hash) && other_value.is_a?(Hash)
          this_value.deep_merge(other_value, &block)
        else
          block_given? && key?(current_key) ? block.call(current_key, this_value, other_value) : other_value
        end
      end
      self
    end
  end

  unless defined?(Rails)
    def except(*keys)
      dup.except!(*keys)
    end
  end

  unless defined?(Rails)
    def except!(*keys)
      keys.each { |k| delete(k) }
      self
    end
  end

  def nillify
    dup.nillify!
  end

  def nillify!
    each do |k, v|
      if !v.nil? && ((v.respond_to?(:blank?) && v.blank?) || (v.respond_to?(:to_s) && v.to_s.blank?))
        self[k] = nil
      end
    end
  end

  def only(*keys)
    dup.only!(*keys)
  end

  def only!(*keys)
    hash = {}
    keys.each { |k| hash[k] = self[k] if self.has_key?(k) }
    replace(hash)
  end

  def rename_keys(*keys)
    dup.rename_keys!(*keys)
  end

  def rename_keys!(*keys)
    keys = Hash[*keys.flatten]
    keys.each { |k, v| self[v] = delete(k) if self[k] }
    self
  end

  unless defined?(Rails)
    def reverse_merge(other_hash)
      other_hash.merge(self)
    end
  end

  unless defined?(Rails)
    def reverse_merge!(other_hash)
      other_hash.merge!(self)
    end
  end

  unless defined?(Rails)
    def slice(*keys)
      keys.each_with_object(self.class.new) { |k, h| h[k] = self[k] if has_key?(k) }
    end
  end

  unless defined?(Rails)
    def slice!(*keys)
      omit = slice(*self.keys - keys)
      hash = slice(*keys)

      hash.default      = default
      hash.default_proc = default_proc if default_proc

      replace(hash)
      omit
    end
  end

  unless defined?(Rails)
    def stringify_keys
      dup.stringify_keys!
    end
  end

  unless defined?(Rails)
    def stringify_keys!
      inject({}) do |options,(k, v)|
        options[k.to_s] = v
        options
      end
    end
  end

  def strip
    select { |k, v| !v.blank? }
  end

  def strip!
    reject! { |k, v| v.blank? }
  end

  unless defined?(Rails)
    def symbolize_keys
      dup.symbolize_keys!
    end
  end

  unless defined?(Rails)
    def symbolize_keys!
      inject({}) do |options, (k, v)|
        options[(k.to_sym rescue k) || k] = v
        options
      end
    end
  end

  def symbolize_and_underscore_keys
    dup.symbolize_and_underscore_keys!
  end

  def symbolize_and_underscore_keys!
    inject({}) do |options, (k, v)|
      options[(k.to_s.gsub(" ", "_").underscore.to_sym rescue k) || k] = v
      options
    end
  end

  unless defined?(Rails)
    def transform_keys(&block)
      dup.transform_keys!(&block)
    end
  end

  unless defined?(Rails)
    def transform_keys!(&block)
      return(enum_for(:transform_keys!)) unless block_given?
      keys.each { |k| self[yield(k)] = delete(k) }
      self
    end
  end

  unless defined?(Rails)
    def transform_values(&block)
      dup.transform_values!(&block)
    end
  end

  unless defined?(Rails)
    def transform_values!(&block)
      return(enum_for(:transform_values!)) unless block_given?
      each { |k, v| self[k] = yield(v) }
    end
  end

end