basic_data = [ ["A", "B", "C", "D"],
               ["E", "F", "G", "H"],
               ["I", "J", "K", "L"] ]

defmodule Spiralizer do

  def spiralize(full_array) do
    cursor = %{x: 0, y: 0}
    matrix = Matrix.create_matrix(full_array)
    max_y = length full_array
    max_x = List.first(full_array) |> length
    step(cursor, matrix, max_x, max_y)
  end

  defp step(cursor, matrix, max_x, max_y, acc \\ "") do
    element = Matrix.at(cursor)
    if length(matrix) == 0 do
      acc
    else
      case cursor do
        %{x: 0, y: ^max_y } ->
          step(%{x: 0, y: max_y - 1 }, List.delete(matrix, element), max_x, max_y, "#{acc} #{element.value}")
        %{x: ^max_x, y: y } ->
          step(%{x: max_x, y: y + 1 }, List.delete(matrix, element), max_x, max_y, "#{acc} #{element.value}")
        %{x: x, y: ^max_y } ->
          step(%{x: x - 1, y: max_y }, List.delete(matrix, element), max_x, max_y, "#{acc} #{element.value}")
        %{x: x, y: y} when x < max_x and y < max_y ->
          step(%{x: x + 1, y: y }, List.delete(matrix, element), max_x, max_y, "#{acc} #{element.value}")
      end
    end
  end
end

defmodule Matrix do

  defmodule Element do
    defstruct position: %{ x: 0, y: 0 }, value: ""
  end

  def create_matrix(arr_of_arr) do
    arr_of_arr |>
    Enum.with_index |>
    Enum.map(fn{arr, index_y} ->
      arr |>
      Enum.with_index |>
      Enum.map(fn{value, index_x} ->
        %Element{position: %{x: index_x, y: index_y }, value: value}
      end)
    end) |>
    List.flatten
  end

  def at(matrix, cursor) do
    Enum.find(matrix, fn(elem) ->
      elem.position == cursor
    end)
  end
end

matrix = Matrix.create_matrix(basic_data)
IO.inspect matrix
IO.inspect Matrix.at(matrix, %{x: 2, y: 1})
IO.inspect Spiralizer.spiralize(basic_data)