defmodule Accomplice.Helpers do
  @moduledoc false

  @doc false
  @spec validate_options(map()) :: map() | {:error, atom()}
  def validate_options(%{minimum: min, ideal: ideal, maximum: max} = options) do
    cond do
      min < 1     -> raise ArgumentError, message: "minimum constraint is below 1"
      max < 1     -> raise ArgumentError, message: "maximum constraint is below 1"
      ideal < 1   -> raise ArgumentError, message: "ideal constraint is below 1"
      min > max   -> raise ArgumentError, message: "minimum constraint is greater than maximum constraint"
      ideal < min -> raise ArgumentError, message: "ideal constraint is less than minimum constraint"
      ideal > max -> raise ArgumentError, message: "ideal constraint s greater than maximum constraint"
      true        -> options
    end
  end
  def validate_options(%{minimum: min, maximum: max} = options) do
    cond do
      min < 1   -> raise ArgumentError, message: "minimum constraint is below 1"
      max < 1   -> raise ArgumentError, message: "maximum constraint is below 1"
      min > max -> raise ArgumentError, message: "minimum constraint is greater than maximum constraint"
      true      -> options
    end
  end
  def validate_options(%{minimum: _} = options) when is_map(options) do
    raise ArgumentError, message: "missing maximum constraint"
  end
  def validate_options(%{maximum: _} = options) when is_map(options) do
    raise ArgumentError, message: "missing minimum constraint"
  end
  def validate_options(options) when is_map(options) do
    raise ArgumentError, message: "missing minimum and maximum constraints"
  end
  def validate_options(_), do: raise ArgumentError, message: "options must be a map"

  @doc false
  @spec pop(list(any())) :: {any(), list(any())} | {nil, list(any())}
  def pop([]), do: {nil, []}
  def pop([head | tail]), do: {head, tail}

  @type actions :: nonempty_list(:add | :complete) | :impossible

  @doc false
  @spec create_actions(list(list(any())), list(any()), map()) :: actions
  def create_actions(current_group, [], %{minimum: minimum, ideal: _, maximum: _}) do
    current_group_length = length(current_group)
    if current_group_length < minimum do
      :impossible
    else
      [:complete]
    end
  end
  def create_actions(current_group, _ungrouped, %{minimum: minimum, ideal: ideal, maximum: maximum}) do
    current_group_length = length(current_group)
    cond do
      current_group_length < minimum ->
        # when the current_group's length is less than the minimum constraint,
        # our only option is to add en element.
        [:add]
      current_group_length == maximum ->
        # when the current_group's length is equal to the maximum constraint,
        # our only option is to complete the group.
        [:complete]
      current_group_length < ideal ->
        # when the current group's length is less than the ideal, we first want
        # to try adding an element if there are any to add, then we'll try
        # completing the group since we know that we're at least at the minimum
        # length.
        [:add, :complete]
      current_group_length == ideal ->
        # when the current group's length is at ideal, we first want to try
        # completing the group, then try adding an element, since we know that
        # we're below the maximum current_group length.
        [:complete, :add]
    end
  end

  @doc false
  @spec generate_memo_key(list(any()), list(any())) :: String.t
  def generate_memo_key(current_group, ungrouped) do
    current_group_string = convert_list_to_string(current_group)
    ungrouped_string     = convert_list_to_string(ungrouped)
    "[#{current_group_string}][#{ungrouped_string}]"
  end

  @spec convert_list_to_string(list(any())) :: String.t
  defp convert_list_to_string(list) when is_list(list) do
    list
    |> Enum.sort
    |> Enum.map(&(inspect &1))
    |> Enum.join(",")
  end
end