def image(size = '300x300', format = 'png', background_color = nil, text_color = nil, text = nil)
raise ArgumentError, "Size should be specified in format 300x300" unless size.match(/^[0-9]+x[0-9]+$/)
raise ArgumentError, "Supported formats are #{SUPPORTED_FORMATS.join(', ')}" unless SUPPORTED_FORMATS.include?(format)
raise ArgumentError, "background_color must be a hex value without '#'" unless background_color.nil? || background_color.match(/((?:^\h{3}$)|(?:^\h{6}$)){1}(?!.*\H)/)
raise ArgumentError, "text_color must be a hex value without '#'" unless text_color.nil? || text_color.match(/((?:^\h{3}$)|(?:^\h{6}$)){1}(?!.*\H)/)
image_url = "https://placehold.it/#{size}.#{format}"
image_url += "/#{background_color}" if background_color
image_url += "/#{text_color}" if text_color
image_url += "?text=#{text}" if text
image_url
end