cache_implementation.ex

# Questions:
# 1. How can I specify that path for the cached item by something other than the URL?
# 2. I'd like to use pieces in the Response to generate the cache location, but then, how do I check if the cached file exists before making the API call?


defmodule Base
  use HTTPoison.Base
  
  # ... Basic HTTPoison Implementation ...
end

defmodule API
  def get!(url)
    Base.API.get!(url)
    |> Map.get(:body)
    |> Map.new
  end
end

defmodule Character
  def get!(url), do: API.get!(url)
  def get(realm, character), do: get_url(realm, name) |> get!
end

defmodule Guild
  def get!(url), do: API.get!(url)
  def get(realm, name), do: get_url(realm, name) |> get!
end

# Caching Implementation ... ?
defmodule Exarmory.Cache do
	defstruct [:region, :realm, :name]

	def get!(module, url, %Exarmory.Cache{ } = cache) do
		location = module.storage(cache) <> ".json" |> String.downcase
		# OR use URL if module.storage/1 is not provided
		case File.read(location) do
			{ :ok, content } -> 
				IO.puts("Found cache ...")
				content
			{ :error, _ } ->
				IO.puts("Making API call ...")
				# Exarmory.API.get!(url)
		end
	end
end

Cache.get!(url)

Use Cache.get! as your primary interface instead of API.get!:

defmodule Cache do
  def get!(url) do
    url
    |> cache_file_for_url()
    |> File.read()
    |> handle_file_read(url)
  end

  defp handle_file_read({:error, _}, url) do
    url
    |> API.get!()
    |> cache_result(url)
  end

  defp handle_file_read({:ok, data}, _) do
    data
  end

  defp cache_result(data, url) do
    url
    |> cache_file_for_url()
    |> File.write!(data)

    data
  end

  defp cache_file_for_url(url) do
    cache_location = Application.get_env(:my_app, :http_cache_path)
    filename = Base.url_encode64(url)

    Path.join(cache_location, filename)
  end
end