bamboo

defmodule Bamboo.SendGridHelper do
  @moduledoc """
  Functions for using features specific to Sendgrid.

  ## Example

      email
      |> with_template("80509523-83de-42b6-a2bf-54b7513bd2aa")
      |> substitute("%name%", "Jon Snow")
      |> substitute("%location%", "Westeros")
  """

  alias Bamboo.Email

  @id_size 36
  @field_name :send_grid_template
  @categories :categories

  @doc """
  Specify the template for SendGrid to use for the context of the substitution
  tags.

  ## Example

      email
      |> with_template("80509523-83de-42b6-a2bf-54b7513bd2aa")
  """
  def with_template(email, template_id) do
    if byte_size(template_id) == @id_size do
      template = Map.get(email.private, @field_name, %{})

      email
      |> Email.put_private(@field_name, set_template(template, template_id))
    else
      raise "expected the template_id parameter to be a UUID 36 characters long, got #{
              template_id
            }"
    end
  end

  @doc """
  Add a tag to the list of substitutions in the SendGrid template.

  The tag must be a `String.t` due to SendGrid using special characters to wrap
  tags in the template.

  ## Example

      email
      |> substitute("%name%", "Jon Snow")
  """
  def substitute(email, tag, value) do
    if is_binary(tag) do
      template = Map.get(email.private, @field_name, %{})

      email
      |> Email.put_private(@field_name, add_substitution(template, tag, value))
    else
      raise "expected the tag parameter to be of type binary, got #{tag}"
    end
  end

  @doc """
  An array of category names for this email. A maximum of 10 categories can be assigned to an email.
  Duplicate categories will be ignored and only unique entries will be sent. 

  ## Example

      email
      |> with_categories("campaign-12345")
  """
  def with_categories(email, categories) when is_list(categories) do
    categories =
      (Map.get(email.private, @categories, []) ++ categories)
      |> MapSet.new()
      |> MapSet.to_list()

    email
    |> Email.put_private(@categories, Enum.slice(categories, 0, 10))
  end

  def with_categories(_email, _categories) do
    raise "expected a list of category strings"
  end

  defp set_template(template, template_id) do
    template
    |> Map.merge(%{template_id: template_id})
  end

  defp add_substitution(template, tag, value) do
    template
    |> Map.update(:substitutions, %{tag => value}, fn substitutions ->
      Map.merge(substitutions, %{tag => value})
    end)
  end
end