defmodule Apostle.Mail do
  defstruct email: nil, from: nil, headers: %{}, layout_id: nil, name: nil, reply_to: nil, template_id: nil, data: %{}, attachments: %{}

  @moduledoc """
  Functions for working with individual emails.
  """

  @doc """
  Generates an `Apostle.Mail` struct based on the supplied options.

  Options:
    * `:email`        - the destination email address
    * `:from`         - the from address
    * `:name`         - not sure. ask @snikch
    * `:reply_to`     - the reply to address
    * `:layout_id`    - the "slug" of your template layout should you not want to use the default
    * `:template_id`  - the "slug" of the template to send
    * `:cc`           - contents of the `CC` header
    * `:bcc`          - contents of the `BCC` header
    * `:headers`      - a `Map` containing additional mail headers to send
    * `:attachments`  - a `List` of paths on the filesystem to files you wish to attach
    * _any_other_key_ - set as template variable values (aka `data`).
  """
  def init opts do
    {%Apostle.Mail{}, opts}
      |> parse_value(:email)
      |> parse_value(:from)
      |> parse_value(:name)
      |> parse_value(:reply_to)
      |> parse_value(:layout_id)
      |> parse_value(:template_id)
      |> parse_header(:cc)
      |> parse_header(:bcc)
      |> parse_attachments
      |> parse_data
  end

  def set_value %Apostle.Mail{}=mail, _key, nil do
    mail
  end

  @doc """
  Set a value on the mail struct.
  """
  def set_value %Apostle.Mail{}=mail, key, value do
    Map.put mail, key, value
  end

  def set_header %Apostle.Mail{}=mail, _name, nil do
    mail
  end

  @doc """
  Set an email header.
  """
  def set_header %Apostle.Mail{}=mail, name, value do
    headers = Map.put mail.headers, name, value
    Map.put mail, :headers, headers
  end

  def set_data %Apostle.Mail{}=mail, _key, nil do
    mail
  end

  @doc """
  Set a key and value to the mail's data (ie template variables)
  """
  def set_data %Apostle.Mail{}=mail, key, value do
    data = Map.put mail.data, key, value
    Map.put mail, :data, data
  end

  @doc """
  Add a file attachment, using a path on the filesystem.
  """
  def add_attachment(%Apostle.Mail{}=mail, path) when is_binary(path) do
    file_name      = Path.basename path
    {:ok, content} = File.read path

    add_attachment mail, file_name, content
  end

  @doc """
  Add a file attachment by passing in a file name and content.
  """
  def add_attachment %Apostle.Mail{}=mail, file_name, content do
    attachments = Map.put mail.attachments, file_name, content
    Map.put mail, :attachments, attachments
  end

  # Move values directly from the options map into the mail struct
  defp parse_value {%Apostle.Mail{}=mail, opts}, key do
    value = Dict.get opts, key
    opts  = Dict.delete opts, key
    mail  = set_value mail, key, value
    {mail, opts}
  end

  # Move header values from the options mail into the mail's header map.
  defp parse_header {%Apostle.Mail{}=mail, opts}, key do
    value = Dict.get opts, key
    opts  = Dict.delete opts, key
    mail  = set_header mail, key, value
    {mail, opts}
  end

  defp parse_attachments {%Apostle.Mail{}=mail, opts} do
    attachments = Dict.get opts, :attachments, []
    mail = Enum.reduce(attachments, mail, fn
      ({file_name, content}, mail) -> add_attachment mail, file_name, content
      (path, mail)                 -> add_attachment mail, path
    end)
    opts = Dict.delete opts, :attachments
    {mail, opts}
  end

  # Merge all remaining options into the mail's data map.
  defp parse_data {%Apostle.Mail{}=mail, opts} do
    Enum.reduce opts, mail, fn({k,v},r)-> set_data r, k, v end
  end
end