module Jekyll::Filters

def array_to_sentence_string(array)
  connector = "and"
  case array.length
  when 0
    ""
  when 1
    array[0].to_s
  when 2
    "#{array[0]} #{connector} #{array[1]}"
  else
    "#{array[0...-1].join(', ')}, #{connector} #{array[-1]}"
  end
end

def cgi_escape(input)
  CGI::escape(input)
end

def date_to_long_string(date)
  time(date).strftime("%d %B %Y")
end

def date_to_rfc822(date)
  time(date).rfc822
end

def date_to_string(date)
  time(date).strftime("%d %b %Y")
end

def date_to_xmlschema(date)
  time(date).xmlschema
end

def group_by(input, property)
  if groupable?(input)
    input.group_by do |item|
      item_property(item, property).to_s
    end.inject([]) do |memo, i|
      memo << {"name" => i.first, "items" => i.last}
    end
  else
    input
  end
end

def groupable?(element)
  element.respond_to?(:group_by)
end

def item_property(item, property)
  if item.respond_to?(:data)
    item.data[property.to_s]
  else
    item[property.to_s]
  end
end

def jsonify(input)
  input.to_json
end

def markdownify(input)
  site = @context.registers[:site]
  converter = site.getConverterImpl(Jekyll::Converters::Markdown)
  converter.convert(input)
end

def number_of_words(input)
  input.split.length
end

def textilize(input)
  site = @context.registers[:site]
  converter = site.getConverterImpl(Jekyll::Converters::Textile)
  converter.convert(input)
end

def time(input)
  case input
  when Time
    input
  when String
    Time.parse(input)
  else
    Jekyll.logger.error "Invalid Date:", "'#{input}' is not a valid datetime."
    exit(1)
  end
end

def uri_escape(input)
  URI.escape(input)
end

def where(input, key, value)
  return input unless input.is_a?(Array)
  input.select { |object| object[key] == value }
end

def xml_escape(input)
  CGI.escapeHTML(input)
end