class Addressable::Template

def transform_partial_capture(mapping, capture, processor = nil,
                              normalize_values = true)
  _, operator, varlist = *capture.match(EXPRESSION)
  vars = varlist.split(",")
  if operator == "?"
    # partial expansion of form style query variables sometimes requires a
    # slight reordering of the variables to produce a valid url.
    first_to_expand = vars.find { |varspec|
      _, name, _ =  *varspec.match(VARSPEC)
      mapping.key?(name) && !mapping[name].nil?
    }
    vars = [first_to_expand] + vars.reject {|varspec| varspec == first_to_expand}  if first_to_expand
  end
  vars.
    inject("".dup) do |acc, varspec|
      _, name, _ =  *varspec.match(VARSPEC)
      next_val = if mapping.key? name
                   transform_capture(mapping, "{#{operator}#{varspec}}",
                                     processor, normalize_values)
                 else
                   "{#{operator}#{varspec}}"
                 end
      # If we've already expanded at least one '?' operator with non-empty
      # value, change to '&'
      operator = "&" if (operator == "?") && (next_val != "")
      acc << next_val
  end
end