Position and set both players' islands

lib/islands_engine/rules.ex

@@ -4,35 +4,70 @@ defmodule IslandEngine.Rules do
   """
   alias __MODULE__
 
-  defstruct state: :initialized
+  defstruct state: :initialized,
+            player1: :islands_not_set,
+            player2: :islands_not_set
 
+  @spec new() :: %IslandEngine.Rules{
+          player1: :islands_not_set,
+          player2: :islands_not_set,
+          state: :initialized
+        }
   @doc """
   Gives game rules.
 
-  Returns ``.
+  Returns `%Rules{}`.
 
   ## Examples
 
       iex> IslandEngine.Island.new()
-      %{}
+      %IslandEngine.Rules{
+      state: :initialized,
+      player1: :islands_not_set,
+      player2: :islands_not_set
+      }
 
   """
   def new(), do: %Rules{}
 
+  @doc """
+  Gives game rules and transitions states and actions. Pattern matches for the current game state and actions possible in that state. For any state/event combination that ends up in catchall, we don’t want to transition the state.
+
+  Returns `{:ok, rules}`.
+
+  ## Examples
+
+      iex> IslandEngine.Island.check(%Rules{state: :initialized} = rules, :add_player)
+      {:ok, %Rules{rules | state: :players_set}}
+
+  """
   def check(%Rules{state: :initialized} = rules, :add_player) do
+    # It makes a decision about whether it’s okay to add another player based on the current state of the game. Does not actually add a player. Calling the check/2 function with :add_player when we’re in the :initialized state returns {:ok, <new rules>} and moves us into the :players_set state
     {:ok, %Rules{rules | state: :players_set}}
   end
 
-  @doc """
-  For any state/event combination that ends up in this catchall, we don’t want to transition the state. By simply returning :error, we don’t transform the value of the :state key. Leaving it unchanged keeps the game in the same state.
+  def check(%Rules{state: :players_set} = rules, {:position_islands, player}) do
+    case Map.fetch!(rules, player) do
+      # If the value for the player key is :islands_not_set, it’s fine for that player to move her islands, so we return {:ok, rules}. If the values is :islands_set, it’s not okay for her to move her islands, so we return :error
+      :islands_set -> :error
+      :islands_not_set -> {:ok, rules}
+    end
+  end
 
-  Returns ``.
+  def check(%Rules{state: :players_set} = rules, {:set_islands, player}) do
+    rules = Map.put(rules, player, :islands_set)
 
-  ## Examples
+    case both_players_islands_set?(rules) do
+      true ->
+        {:ok, %Rules{rules | state: :player1_turn}}
 
-      iex> IslandEngine.Island.new()
-      %{}
+      false ->
+        {:ok, rules}
+    end
+  end
 
-  """
   def check(_state, _action), do: :error
+
+  defp both_players_islands_set?(rules),
+    do: rules.player1 == :islands_set && rules.player2 == :islands_set
 end