defmodule SplitClient do
  @moduledoc """
  A Split.io client for Elixir.

  See [Glossary](README.md#split-io-glossary) for explanations about
  function arguments and return values
  """

  alias SplitClient.Boundary.Treatments

  @doc """
  Get the treatment for a specific split.

  ## Args

  * `key`
  * `split_name`

  ## Options

  * `:attributes`
  * `:bucketing_key`
  * `:cache` - (defaults to true) By default the SplitClient caches evaluation results. To ignore the cache and make a direct request
  to the split-evaluator pass `false` here. This only affects reads. Results will still added to the cache.

  ## Examples

      iex> SplitClient.get_treatment("unique-customer-id", "shiny-feature")
      %Treatment{split_name: "shiny-feature", treatment: "on"}
  """
  @spec get_treatment(key :: String.t(), split_name :: String.t(), options :: keyword()) ::
          Treatment.t()
  def get_treatment(key, split_name, opts \\ []) do
    validate_params([
      &validate_key(&1, key, "key"),
      &validate_key(&1, split_name, "split_name"),
      &validate_optional(&1, opts, :bucketing_key),
      &validate_optional(&1, opts, :attributes)
    ])

    treatments_server().get_treatment(key, split_name, opts)
  end

  @doc """
  Get the treatments for multiple splits.

  ## Args

  * `key`
  * `split_name`

  ## Options

  * `:attributes`
  * `:bucketing_key`
  * `:cache` - (defaults to true) By default the SplitClient caches evaluation results. To ignore the cache and make a direct request
  to the split-evaluator pass `false` here. This only affects reads. Results will still added to the cache.

  ## Examples

      iex> SplitClient.get_treatments("unique-customer-id", ["shiny-feature", "my-experiment"])
      %{"shiny-feature" => %Treatment{treatment: "on"}, "my-experiment" => %Treatment{split_name: "my-experiment", treatment: "off"}}
  """
  @spec get_treatments(key :: String.t(), split_names :: [String.t()], options :: keyword()) ::
          map()
  def get_treatments(key, split_names, opts \\ []) do
    validate_params([
      &validate_key(&1, key, "key"),
      &validate_keys(&1, split_names, "split_name"),
      &validate_optional(&1, opts, :bucketing_key),
      &validate_optional(&1, opts, :attributes)
    ])

    treatments_server().get_treatments(key, split_names, opts)
  end

  @doc """
  Get all the treatments for one or more traffic types.

  ## Args

  * `keys` - A list of maps containing the following:
    - `:matching_key`
    - `:traffic_type`
    - `:bucketing_key` - Optional

  ## Options

  * `:attributes`

  ## Examples

      iex> SplitClient.get_all_treatments(%{matching_key: "unique-customer-id", target_type: "customer"}, %{matching_key: "unique-user-id", target_type: "user"})
      %{"customer" => %{"shiny-feature" => %Treatment{treatment: "on"}}, "user" => %{"my-experiment" => %Treatment{treatment: "off"}}}
  """
  @spec get_all_treatments(keys :: [map()], options :: keyword()) :: map()
  def get_all_treatments(keys, opts \\ []) do
    validate_params([
      &validate_composite_keys(&1, keys),
      &validate_optional(&1, opts, :attributes)
    ])

    treatments_server().get_all_treatments(keys, opts)
  end

  @doc """
  Determine if a particular split is turned on. This is syntax sugar around the
  `get_treatment/3` function. If your treatment has a meaningful config that
  could be returned then use `get_treatment/3` instead

  ## Args

  * `key`
  * `split_name`

  ## Options

  * `:attributes`
  * `:bucketing_key`
  * `:cache` - (defaults to true) By default the SplitClient caches evaluation results. To ignore the cache and make a direct request
  to the split-evaluator pass `false` here. This only affects reads. Results will still added to the cache.

  ## Examples

      iex> SplitClient.on?("unique-customer-id", "shiny-feature")
      true
  """
  @spec on?(key :: String.t(), split_name :: String.t(), options :: keyword()) ::
          boolean()
  def on?(key, split_name, opts \\ []) do
    treatment = get_treatment(key, split_name, opts)
    treatment.treatment == "on"
  end

  @doc """
  Determine if a particular split is turned off. This is syntax sugar around the
  `get_treatment/3` function. If your treatment has a meaningful config that
  could be returned then use `get_treatment/3` instead

  ## Args

  * `key`
  * `split_name`

  ## Options

  * `:attributes`
  * `:bucketing_key`
  * `:cache` - (defaults to true) By default the SplitClient caches evaluation results. To ignore the cache and make a direct request
  to the split-evaluator pass `false` here. This only affects reads. Results will still added to the cache.

  ## Examples

      iex> SplitClient.off?("unique-customer-id", "shiny-feature")
      true
  """
  @spec off?(key :: String.t(), split_name :: String.t(), options :: keyword()) ::
          boolean()
  def off?(key, split_name, opts \\ []) do
    treatment = get_treatment(key, split_name, opts)
    treatment.treatment != "on"
  end

  defp validate_params(validators) do
    errors =
      Enum.reduce(validators, [], fn validator, acc ->
        validator.(acc)
      end)

    if !Enum.empty?(errors) do
      raise __MODULE__.InvalidParamsException, errors
    end
  end

  defp validate_optional(errors, opts, option) do
    case Keyword.has_key?(opts, option) do
      true ->
        validate_option(errors, Keyword.get(opts, option), option)

      false ->
        errors
    end
  end

  defp validate_option(errors, bucketing_key, :bucketing_key) do
    validate_key(errors, bucketing_key, "bucketing_key")
  end

  defp validate_option(errors, attributes, :attributes) when is_list(attributes), do: errors
  defp validate_option(errors, attributes, :attributes) when is_map(attributes), do: errors

  defp validate_option(errors, attributes, :attributes) do
    add_error(errors, "`attributes` must be a map or keyword list, got `#{inspect(attributes)}`")
  end

  defp validate_composite_keys(errors, keys) when is_list(keys) and length(keys) > 0 do
    Enum.reduce(keys, errors, fn key, acc ->
      validate_composite_key(acc, key)
    end)
  end

  defp validate_composite_keys(errors, keys) do
    add_error(errors, "`keys` must be a list with at least 1 item, got #{inspect(keys)}")
  end

  defp validate_composite_key(errors, %{matching_key: matching, traffic_type: traffic_type} = key) do
    validate_optional(errors, Enum.into(key, Keyword.new()), :bucketing_key)
    |> validate_key(matching, "matching_key")
    |> validate_key(traffic_type, "traffic_type")
  end

  defp validate_composite_key(errors, key) do
    add_error(
      errors,
      "`key` must be a map with a `matching_key` and `traffic_type`, got #{inspect(key)}"
    )
  end

  defp validate_keys(errors, keys, key_name) when is_list(keys) do
    Enum.reduce(keys, errors, fn key, acc ->
      validate_key(acc, key, key_name)
    end)
  end

  defp validate_key(errors, nil, key_name),
    do: [non_empty_string_msg(key_name, nil) | errors]

  defp validate_key(errors, key, key_name) when is_binary(key) do
    errors =
      case String.trim(key) do
        "" -> add_error(errors, non_empty_string_msg(key_name, key))
        _key -> errors
      end

    case String.length(key) > 250 do
      true ->
        add_error(errors, "`#{key_name}` must be less than 250 characters, got `#{inspect(key)}`")

      false ->
        errors
    end
  end

  defp validate_key(errors, key, key_name) when is_atom(key) do
    validate_key(errors, Atom.to_string(key), key_name)
  end

  defp validate_key(errors, key, key_name) when is_integer(key) do
    validate_key(errors, Integer.to_string(key), key_name)
  end

  defp validate_key(errors, key, key_name) do
    add_error(errors, non_empty_string_msg(key_name, key))
  end

  defp add_error(errors, error) do
    [error | errors]
  end

  defp non_empty_string_msg(key_name, key) do
    "`#{key_name}` must be a non-empty string, got `#{inspect(key)}`"
  end

  defp treatments_server do
    Application.get_env(:split_client, :treatments_server, Treatments)
  end

  defmodule InvalidParamsException do
    @moduledoc false
    defexception [:message]

    @impl true
    def exception(errors) do
      msg = Enum.join(errors, "\n")

      %__MODULE__{message: msg}
    end
  end
end