post.ex

defmodule Feed.S3.Sync.Post do
  defstruct title: "",
    summary: "",
    content: "",
    filename: "",
    author: "",
    cover_image: "",
    tags: [],
    published_at: "",
    published: false

  alias __MODULE__

  @options %Earmark.Options{code_class_prefix: "language-"}

  def compile(file) do
    file
    |> split()
    |> extract()
  end

  defp split(data) do
    [frontmatter, markdown] = String.split(data, ~r/\n-{3,}\n/, parts: 2)
    {parse_yaml(frontmatter), Earmark.as_html!(markdown, @options)}
  end

  defp parse_yaml(yaml) do
    [parsed] = :yamerl_constr.string(yaml)
    parsed
  end

  defp extract({props, content}) do
    %Post{
      title: get_prop(props, "title"),
      summary: get_prop(props, "summary"),
      author: get_prop(props, "author"),
      content: content,
      cover_image: get_prop(props, "image"),
      tags: get_prop(props, "tags"),
      published_at: get_date_prop(props, "date"),
      published: get_boolean_prop(props, "published")
    }
  end

  defp get_prop(props, key) do
    parse_value(props, key)
  end

  def get_date_prop(props, field) do
    props
    |> get_prop(field)
    |> Timex.parse!("%Y-%m-%d %H:%M:%S", :strftime)
  end

  def get_boolean_prop(props, field) do
    props
    |> get_prop(field)
    |> convert_to_boolean()
  end

  defp parse_value(props, "tags") do
    case get_value(props, "tags") do
      :undefined -> nil
      list ->
        Enum.map(list, fn item -> to_string(item) end)
    end
  end

  defp parse_value(props, key) do
    case get_value(props, key) do
      :undefined -> nil
      x ->
        to_string(x)
    end
  end

  defp get_value(props, key) do
    :proplists.get_value(String.to_charlist(key), props)
  end

  def convert_to_boolean("true"), do: true
  def convert_to_boolean("false"), do: false
end