defmodule Reactor.Argument do
  @moduledoc """
  A step argument.
  """

  defstruct description: nil, name: nil, source: nil, transform: nil

  alias Reactor.{Argument, Template}
  import Reactor.Template, only: :macros

  @options Spark.Options.new!(
             transform: [
               type:
                 {:or,
                  [
                    nil,
                    {:mfa_or_fun, 1},
                    {:tuple, [:module, :non_empty_keyword_list]}
                  ]},
               required: false,
               default: nil,
               doc: """
               An optional transformation function which can be used to modify the argument before it is passed to the step.
               """
             ],
             description: [
               type: {:or, [nil, :string]},
               required: false,
               default: nil,
               doc: """
               An optional description for the argument.
               """
             ]
           )

  @type transform :: nil | (any -> any) | {module, keyword} | mfa

  @type t :: %Argument{
          description: nil | String.t(),
          name: atom,
          source: Template.t(),
          transform: transform
        }

  @type options :: [{:description, nil | String.t()} | {:transform, transform}]

  defguardp is_spark_fun_behaviour(fun)
            when tuple_size(fun) == 2 and is_atom(elem(fun, 0)) and is_list(elem(fun, 1))

  defguardp is_mfa(fun)
            when tuple_size(fun) == 3 and is_atom(elem(fun, 0)) and is_atom(elem(fun, 1)) and
                   is_list(elem(fun, 2))

  defguardp is_transform(fun)
            when is_function(fun, 1) or is_spark_fun_behaviour(fun) or is_mfa(fun)

  defguardp maybe_options(options)
            when is_nil(options) or is_list(options) or is_transform(options)

  @doc """
  Build an argument which refers to a reactor input with an optional
  transformation applied.

  ## Options

  #{Spark.Options.docs(@options)}

  ## Example

      iex> Argument.from_input(:argument_name, :input_name, transform: &String.to_integer/1)

  """
  @spec from_input(atom, atom, nil | (any -> any) | options) :: Argument.t()
  def from_input(name, input_name, options \\ nil)
      when is_atom(name) and maybe_options(options) do
    options = validate_options!(options)

    %Argument{
      description: options[:description],
      name: name,
      source: %Template.Input{name: input_name},
      transform: options[:transform]
    }
  end

  @doc """
  Build an argument which refers to the result of another step with an optional
  transformation applied.

  ## Example

      iex> Argument.from_result(:argument_name, :step_name, &Atom.to_string/1)

  """
  @spec from_result(atom, any, nil | (any -> any) | options) :: Argument.t()
  def from_result(name, result_name, options \\ nil)
      when is_atom(name) and maybe_options(options) do
    options = validate_options!(options)

    %Argument{
      description: options[:description],
      name: name,
      source: %Template.Result{name: result_name},
      transform: options[:transform]
    }
  end

  @doc """
  Build an argument which refers to a statically defined value.

  ## Example

      iex> Argument.from_value(:argument_name, 10)
  """
  @spec from_value(atom, any, nil | (any -> any) | options) :: Argument.t()
  def from_value(name, value, options \\ nil) when is_atom(name) and maybe_options(options) do
    options = validate_options!(options)

    %Argument{
      description: options[:description],
      name: name,
      source: %Template.Value{value: value},
      transform: options[:transform]
    }
  end

  @doc """
  Build an argument which refers to to an element within a map step with an optional transformation applied.

  ## Example

      iex> Argument.from_element(:argument_name, &Atom.to_string/1)

  """
  @spec from_element(any, any, nil | (any -> any) | options) :: Argument.t()
  def from_element(name, element_name, options \\ nil)
      when maybe_options(options) do
    options = validate_options!(options)

    %Argument{
      description: options[:description],
      name: name,
      source: %Template.Element{name: element_name},
      transform: options[:transform]
    }
  end

  @doc """
  Build an argument directly from a template.

  ## Example

      iex> Argument.from_template(:argument_name, Reactor.Dsl.Argument.input(:input_name))

  """
  @spec from_template(atom, Template.t(), nil | (any -> any) | options) :: Argument.t()
  def from_template(name, template, options \\ nil)
      when is_atom(name) and is_template(template) and maybe_options(options) do
    options = validate_options!(options)

    %Argument{
      description: options[:description],
      name: name,
      source: template,
      transform: options[:transform]
    }
  end

  @doc """
  Set a sub-path on the argument.

  ## Example

      iex> Argument.from_value(:example, :value)
      ...> |> Argument.sub_path([:nested, :values])

  """
  @spec sub_path(Argument.t(), [any]) :: Argument.t()
  def sub_path(argument, sub_path),
    do: %{argument | source: %{argument.source | sub_path: sub_path}}

  @doc """
  Validate that the argument is an Argument struct.
  """
  defguard is_argument(argument) when is_struct(argument, __MODULE__)

  @doc """
  Validate that the argument refers to a reactor input.
  """
  defguard is_from_input(argument)
           when is_argument(argument) and is_input_template(argument.source)

  @doc """
  Validate that the argument refers to a step result.
  """
  defguard is_from_result(argument)
           when is_argument(argument) and is_result_template(argument.source)

  @doc """
  Validate that the argument contains a static value.
  """
  defguard is_from_value(argument)
           when is_argument(argument) and is_value_template(argument.source)

  @doc """
  Validate that the argument contains an element.
  """
  defguard is_from_element(argument)
           when is_argument(argument) and is_element_template(argument.source)

  @doc """
  Validate that the argument has a transform.
  """
  defguard has_transform(argument) when is_transform(argument.transform)

  @doc """
  Validate that the argument source has a sub_path
  """
  defguard has_sub_path(argument)
           when is_list(argument.source.sub_path) and argument.source.sub_path != []

  defp validate_options!(options) when is_list(options),
    do: Spark.Options.validate!(options, @options)

  defp validate_options!(transform),
    do: validate_options!(transform: transform)
end