defmodule Irc.Parser.Prefix do

  @moduledoc """
  Parser for prefixes.

  Supports multi-prefix.
  """

  @spec parse(String.t, Irc.Connection.t) :: {modes :: [String.t], rest :: nil | String.t}
  @doc """
  If `lax` is set to true, the parser will ignore chars until it meets a known prefix.
  """
  def parse(string, conn, lax \\ false) do
    map = Map.get(conn.isupport, "PREFIX") || %{}
    {prefixes, rest} = parse_prefix(string, Map.keys(map), lax)
    modes = Enum.map(prefixes, fn(p) -> Map.get(map, p) end)
            |> Enum.filter(fn(p) -> p end)
    {Enum.reverse(modes), to_string(Enum.reverse(rest))}
  end

  defp parse_prefix(string, all_prefixes, lax) do
    parse_prefix(to_charlist(string), to_charlist(all_prefixes), [], [], lax)
  end

  defp parse_prefix(all = [prefix | rest], all_prefixes, acc, ign, lax) do
    prefix_str = to_string([prefix])
    cond do
      Enum.member?(all_prefixes, prefix_str) -> parse_prefix(rest, all_prefixes, [prefix_str | acc], ign, lax)
      lax && acc == [] -> parse_prefix(rest, all_prefixes, acc, [prefix | ign], lax)
      true -> parse_lax(all, acc, [])
    end
  end

  defp parse_prefix([], _, acc, ign, _) do
    {acc, ign}
  end

  defp parse_lax([a | rest], prefixes, acc) do
    parse_lax(rest, prefixes, [a | acc])
  end

  defp parse_lax([], prefixes, acc) do
    {prefixes, acc}
  end

end