defmodule ConsulConfigProvider do
  @moduledoc "A consul config provider for Elixir 1.9+ assuming the configs have an extension in the key name"
  @behaviour Config.Provider
  @dialyzer {:nowarn_function, load: 2}

  @impl true
  def init(%{prefix: prefix} = consul_config) when is_binary(prefix) do
    consul_config
  end

  @impl true
  def load(config, %{prefix: prefix}) do
    host = System.get_env("CONSUL_HOST", "localhost")
    port = System.get_env("CONSUL_PORT", "8500") |> String.to_integer()
    prefix = System.get_env("CONSUL_PREFIX", prefix)
    keys_url = "http://#{host}:#{port}/v1/kv/#{prefix}?keys=true"

    http_module =
      get_in(config, [:consul_config_provider, :http_module])
      |> case do
        nil -> ConsulConfigProvider.Client.Finch
        mod -> mod
      end

    transformer_module = get_in(config, [:consul_config_provider, :transformer_module])

    {:ok, body} = http_module.request(method: :get, url: keys_url)

    consul_configs =
      body
      |> Jason.decode!()
      |> Enum.reduce([], fn path, acc ->
        if String.ends_with?(path, "/") do
          acc
        else
          [String.replace_leading(path, prefix <> "/", "") | acc]
        end
      end)
      |> Enum.map(
        &Task.async(fn ->
          get_consul_key(http_module, host, port, prefix, &1)
        end)
      )
      |> Enum.map(&Task.await/1)

    Enum.reduce(consul_configs, config, fn cfg, acc ->
      {key, value} =
        case transformer_module do
          nil -> cfg
          _ -> transformer_module.transform(cfg)
        end

      Config.Reader.merge(
        acc,
        [{key, value}]
      )
    end)
  end

  defp get_consul_key(http_module, host, port, prefix, key_name) do
    url = "http://#{host}:#{port}/v1/kv/#{prefix}/#{key_name}"
    {:ok, body} = http_module.request(method: :get, url: url)

    key_val =
      body
      |> Jason.decode!()
      |> hd()
      |> Map.get("Value")
      |> Base.decode64!()

    new_config =
      key_name
      |> Path.extname()
      |> case do
        ".json" ->
          key_val |> Jason.decode!() |> Map.to_list()

        ".yml" ->
          key_val |> YamlElixir.read_from_string!(maps_as_keywords: true, atoms: true)

        ".yaml" ->
          key_val |> YamlElixir.read_from_string!(maps_as_keywords: true, atoms: true)

        _ ->
          raise "unsupported config format"
      end
      |> string_atoms()

    config_prefix =
      key_name
      |> Path.rootname()
      |> String.to_atom()

    {config_prefix, new_config}
  end

  defp string_atoms(list, acc \\ [])

  defp string_atoms([], acc) do
    Enum.reverse(acc)
  end

  defp string_atoms([{str, val} | rest], acc) when is_binary(str) and is_list(val) do
    string_atoms(rest, [{String.to_atom(str), string_atoms(val)} | acc])
  end

  defp string_atoms([{str, val} | rest], acc) when is_binary(str) do
    string_atoms(rest, [{String.to_atom(str), val} | acc])
  end

  defp string_atoms([item | rest], acc) do
    string_atoms(rest, [item | acc])
  end
end