-module(movement).

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% TYPES %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% EXPORTS %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

-export
(
   [
      cross/4,
      steps_between/2
   ]
).

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% LOCAL FUNCTIONS %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
location_after_step (Step, X, Y) ->
   case Step of
      <<"L">> -> {(X - 1), Y};
      <<"R">> -> {(X + 1), Y};
      <<"U">> -> {X, (Y - 1)};
      <<"D">> -> {X, (Y + 1)}
   end.

location_to_array_index (ArrayWidth, X, Y) ->
   if
      (X < 0) -> -1;
      (Y < 0) -> -1;
      (X >= ArrayWidth) -> error;
      true -> ((Y * ArrayWidth) + X)
   end.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% EXPORTED FUNCTIONS %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
cross (_Battlemap, _ForbiddenLocations, [], Cost, X, Y) ->
   {{X, Y}, Cost};
cross (Battlemap, ForbiddenLocations, [Step|NextSteps], Cost, X, Y) ->
   BattlemapTiles = battlemap:get_tiles(Battlemap),

   {NextX, NextY} = location_after_step(Step, X, Y),
   NextTileIX =
      location_to_array_index(array:size(BattlemapTiles), NextX, NextY),
   NextTile = array:get(array:get(NextTileIX, BattlemapTiles)),
   NextCost = (Cost + tile:get_cost(NextTile)),
   IsForbidden =
      array:foldl
      (
         fun (_IX, Location, Prev) ->
            (Prev or ({NextX, NextY} == Location))
         end,
         ForbiddenLocations
      ),

   IsForbidden = false,

   cross(Battlemap, ForbiddenLocations, NextSteps, NextCost, NextX, NextY).

cross (Battlemap, ForbiddenLocations, Path, {X, Y}) ->
   cross(Battlemap, ForbiddenLocations, Path, 0, X, Y).

steps_between ({OX, OY}, {DX, DY}) ->
   (abs(DY - OY) + abs(DX - OX)).