defmodule ActivityPub.Headers.SignatureSplitter do
  def split(""), do: []

  def split(value) do
    {key_value, rest} = scan_until(value, ",")
    {key, value} = split_kv(key_value)

    [{key, value} | split(rest)]
  end

  defp split_kv(kv_string) do
    {key, wrapped_value} = scan_until(kv_string, "=")
    value = String.trim(wrapped_value, ~s("))
    {key, value}
  end

  def scan_until(buffer, terminator, acc \\ "")

  def scan_until("", _terminator, acc), do: {acc, ""}

  def scan_until(<<ch::utf8, buffer::binary>>, terminator, acc) do
    ch = <<ch>>

    if ch == terminator do
      {acc, buffer}
    else
      scan_until(buffer, terminator, acc <> ch)
    end
  end
end