defmodule ElixirFeedParser.XmlNode do

  # see https://github.com/erlang/otp/blob/maint/lib/xmerl/include/xmerl.hrl
  # for Record definitions of xmlElement, xmlAttribute, xmlText

  def parse_string(xml_string, options \\ [quiet: true]) do
    {doc, []} = xml_string |> :binary.bin_to_list |> :xmerl_scan.string(options)
    doc
  end

  def find(node, path) do
    xpath(node, path) |> List.first
  end

  def map_children(node, selector, callback) do
    node |> children(selector) |> Enum.map(callback)
  end

  def children(node, selector) do
    node |> xpath("./#{selector}")
  end

  def attr(nil, _name), do: nil
  def attr(node, name) do
    node |> xpath("./@#{name}") |> extract_attr
  end

  defp extract_attr(nil), do: nil
  defp extract_attr([]), do: nil
  defp extract_attr([{:xmlAttribute, _name, _expanded_name, _nsinfo, _namespace, _parents, _pos, _language, value, _normalized}]) do
    List.to_string(value)
  end


  def text(node) do
    node |> xpath("./text()") |> extract_text
  end

  defp extract_text(nil), do: nil
  defp extract_text([]), do: nil
  defp extract_text({:xmlText, _parents, _pos, _language, value, _type}) do
    List.to_string(value)
  end
  defp extract_text([head | tail]) do
    "#{extract_text(head)}#{extract_text(tail)}"
  end

  def xpath(nil, path), do: nil
  def xpath(node, path) do
    :xmerl_xpath.string(to_char_list(path), node)
  end

  def namespace(nil), do: nil
  def namespace({:xmlElement, _name, _expanded_name, _nsinfo, {:xmlNamespace, default, _nodes}, _parents, _pos, _attributes, _content, _language, _xmlbase, _elementdef}) do
    Atom.to_string(default)
  end

  def namespaces({:xmlElement, _name, _expanded_name, _nsinfo, {:xmlNamespace, default, nodes}, _parents, _pos, _attributes, _content, _language, _xmlbase, _elementdef}) do
    result = Enum.map(nodes, fn(n) ->
      {key, value} = n;
      {List.to_string(key), Atom.to_string(value)}
    end)

    Enum.into(result, HashDict.new)
  end

end