matplotex

defmodule Matplotex.Figure.Areal.Step do
  @moduledoc false
  alias Matplotex.Figure.Areal.LinePlot
  alias Matplotex.Figure
  alias Matplotex.InputError

  def create(x, y, opts) do
    {x, y} = step_segments(x, y)
    LinePlot.create(%Figure{axes: %LinePlot{}}, {x, y}, opts)
  end

  def create(%Figure{} = figure, x, y, opts) do
    {x, y} = step_segments(x, y)
    LinePlot.create(figure, {x, y}, opts)
  end

  defp step_segments(x, y) do
    x = horizontal_segments(x)
    y = vertical_segments(y)
    {x, y}
  end

  defp horizontal_segments(data) when is_list(data) do
    first_value = List.first(data)
    second_last_index = length(data) - 1
    repeated = data |> Enum.slice(1..second_last_index) |> List.duplicate(2) |> List.flatten()
    [first_value | repeated] |> Enum.sort()
  end

  defp horizontal_segments(_data), do: list_error(:y)

  defp vertical_segments(data) when is_list(data) do
    data |> List.duplicate(2) |> List.flatten() |> Enum.sort()
  end

  defp vertical_segments(_data), do: list_error(:y)

  defp list_error(arg) do
    raise InputError, message: "Expected a list for arg: #{arg}"
  end
end