defmodule MarsExplorer.Exploration do
  @moduledoc """
  Module responsible for managing a exploration
  """
  alias MarsExplorer.{Probe, Exploration, HighlandGrid}
  defstruct [:grid, :probe]

  @type placement :: %{
          north: integer,
          east: integer,
          direction: :west | :north | :south | :east
        }

  @type t :: %__MODULE__{
          grid: MarsExplorer.HighlandGrid.t(),
          probe: MarsExplorer.Probe.t()
        }

  @doc """
  Places a probe on a grid

  ## Examples

  When the probe is placed in a valid position

      iex> alias MarsExplorer.{Probe, Exploration, HighlandGrid}
      [MarsExplorer.Probe, MarsExplorer.Exploration, MarsExplorer.HighlandGrid]
      iex> grid = HighlandGrid.build(%{north: 5, east: 5})
      %HighlandGrid{north_limit: 5, east_limit: 5}
      iex> Exploration.place(grid, %{north: 0, east: 0, direction: :north})
      {
        :ok,
        %Exploration{
          grid: grid,
          probe: %Probe{north: 0, east: 0, direction: :north}
        }
      }

  When the probe is placed in a invalid position

      iex> alias MarsExplorer.{Exploration, HighlandGrid}
      [MarsExplorer.Exploration, MarsExplorer.HighlandGrid]
      iex> grid = HighlandGrid.build(%{north: 5, east: 5})
      %HighlandGrid{north_limit: 5, east_limit: 5}
      iex> Exploration.place(grid, %{north: 6, east: 6, direction: :north})
      {:error, :invalid_placement}
  """
  @spec place(HighlandGrid.t(), placement()) :: {:ok, t()} | {:error, :invalid_placement}
  def place(grid, placement) do
    if grid |> HighlandGrid.valid_position?(placement) do
      {
        :ok,
        %Exploration{
          grid: grid,
          probe: struct(Probe, placement)
        }
      }
    else
      {:error, :invalid_placement}
    end
  end

  @doc """
  Moves the probe forward one unit in the direction that it is facing, unless that position is past the limits of the grid.

  ## Examples

  ### A valid movement

      iex> alias MarsExplorer.{Probe, HighlandGrid, Exploration}
      [MarsExplorer.Probe, MarsExplorer.HighlandGrid, MarsExplorer.Exploration]
      iex> grid = HighlandGrid.build(%{north: 5, east: 5})
      %HighlandGrid{north_limit: 5, east_limit: 5}
      iex> exploration = %Exploration{
      ...> grid: grid,
      ...> probe: %Probe{north: 0, east: 0, direction: :north}
      ...> }
      iex> exploration |> Exploration.move
      {:ok, %Exploration{
        grid: grid,
        probe: %Probe{north: 1, east: 0, direction: :north}
      }}

  ### An invalid movement:

      iex> alias MarsExplorer.{Probe, HighlandGrid, Exploration}
      [MarsExplorer.Probe, MarsExplorer.HighlandGrid, MarsExplorer.Exploration]
      iex> grid = HighlandGrid.build(%{north: 5, east: 5})
      %HighlandGrid{north_limit: 5, east_limit: 5}
      iex> exploration = %Exploration{
      ...> grid: grid,
      ...> probe: %Probe{north: 5, east: 0, direction: :north}
      ...> }
      iex> exploration |> Exploration.move()
      {:error, :at_grid_limit}

  """
  @spec move(t()) :: {:ok, t()} | {:error, :at_grid_limit}
  def move(%{probe: probe, grid: grid} = exploration) do
    with moved_probe <- probe |> Probe.move(),
         true <- grid |> HighlandGrid.valid_position?(moved_probe) do
      {:ok, %{exploration | probe: moved_probe}}
    else
      false -> {:error, :at_grid_limit}
    end
  end

  @doc """
  Turns the probe left.

  ## Examples

      iex> alias MarsExplorer.{Probe, HighlandGrid, Exploration}
      [MarsExplorer.Probe, MarsExplorer.HighlandGrid, MarsExplorer.Exploration]
      iex> grid = HighlandGrid.build(%{north: 5, east: 5})
      %HighlandGrid{north_limit: 5, east_limit: 5}
      iex> exploration = %Exploration{
      ...> grid: grid,
      ...> probe: %Probe{north: 0, east: 0, direction: :north}
      ...> }
      iex> exploration |> Exploration.turn_left
      {:ok, %Exploration{
        grid: grid,
        probe: %Probe{north: 0, east: 0, direction: :west}
      }}
  """
  @spec turn_left(t()) :: {:ok, t()}
  def turn_left(%Exploration{probe: probe} = exploration) do
    {:ok, %{exploration | probe: probe |> Probe.turn_left()}}
  end

  @doc """
  Turns the probe left.

  ## Examples

      iex> alias MarsExplorer.{Probe, HighlandGrid, Exploration}
      [MarsExplorer.Probe, MarsExplorer.HighlandGrid, MarsExplorer.Exploration]
      iex> grid = HighlandGrid.build(%{north: 5, east: 5})
      %HighlandGrid{north_limit: 5, east_limit: 5}
      iex> exploration = %Exploration{
      ...> grid: grid,
      ...> probe: %Probe{north: 0, east: 0, direction: :north}
      ...> }
      iex> exploration |> Exploration.turn_right
      {:ok, %Exploration{
        grid: grid,
        probe: %Probe{north: 0, east: 0, direction: :east}
      }}
  """
  @spec turn_right(t()) :: {:ok, t()}
  def turn_right(%Exploration{probe: probe} = exploration) do
    {:ok, %{exploration | probe: probe |> Probe.turn_right()}}
  end

  @doc """
  Returns the probe's current position.

  ## Examples

      iex> alias MarsExplorer.{Probe, HighlandGrid, Exploration}
      [MarsExplorer.Probe, MarsExplorer.HighlandGrid, MarsExplorer.Exploration]
      iex> grid = HighlandGrid.build(%{north: 5, east: 5})
      %HighlandGrid{north_limit: 5, east_limit: 5}
      iex> exploration = %Exploration{
      ...> grid: grid,
      ...> probe: %Probe{north: 0, east: 0, direction: :north}
      ...> }
      iex> exploration |> Exploration.report
      %Probe{north: 0, east: 0, direction: :north}
  """
  @spec report(t()) :: {:ok, Probe.t()}
  def report(%Exploration{probe: probe}), do: probe
end