[Broken] ...

4 files changed, 1190 insertions, 0 deletions

diff --git a/src/battle/mechanic/action/btl_action_attack.erl b/src/battle/mechanic/action/btl_action_attack.erl
new file mode 100644
index 0000000..1241735
--- /dev/null
+++ b/src/battle/mechanic/action/btl_action_attack.erl
@@ -0,0 +1,655 @@
+-module(btl_turn_actions_attack).
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%% TYPES %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%% EXPORTS %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+-export
+(
+   [
+      handle/3
+   ]
+).
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%% LOCAL FUNCTIONS %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+-spec roll_precision_modifier
+   (
+      shr_statistics:type(),
+      shr_statistics:type(),
+      integer()
+   )
+   -> {float(), integer(), integer()}.
+roll_precision_modifier (Statistics, TargetStatistics, TargetLuck) ->
+   TargetDodges = shr_statistics:get_dodges(TargetStatistics),
+   Accuracy = shr_statistics:get_accuracy(Statistics),
+   MissChance = max(0, (TargetDodges - Accuracy)),
+
+   {Roll, _IsSuccess, PositiveModifier, NegativeModifier} =
+      shr_roll:percentage_with_luck(MissChance, TargetLuck),
+
+   {
+      case Roll of
+         X when (X =< MissChance) -> 0.0;
+         X when (X =< (MissChance * 2)) -> 0.5;
+         _ -> 1.0
+      end,
+      PositiveModifier,
+      NegativeModifier
+   }.
+
+-spec roll_critical_hit_modifier
+   (
+      shr_statistics:type(),
+      integer()
+   )
+   -> {boolean(), integer(), integer()}.
+roll_critical_hit_modifier (Statistics, Luck) ->
+   CriticalHitChance = shr_statistics:get_critical_hits(Statistics),
+   {_Roll, IsSuccess, PositiveModifier, NegativeModifier} =
+      shr_roll:percentage_with_luck(CriticalHitChance, Luck),
+
+   {
+      case IsSuccess of
+         true -> 2.0; % [TODO][FUTURE]: variable critical multiplier?
+         false -> 1.0
+      end,
+      PositiveModifier,
+      NegativeModifier
+   }.
+
+-spec roll_parry
+   (
+      shr_statistics:type(),
+      integer()
+   )
+   -> {boolean(), integer(), integer()}.
+roll_parry (DefenderStatistics, DefenderLuck) ->
+   DefenderParryChance = shr_statistics:get_parries(DefenderStatistics),
+   {_Roll, IsSuccess, PositiveModifier, NegativeModifier} =
+      shr_roll:percentage_with_luck(DefenderParryChance, DefenderLuck),
+
+   {IsSuccess, PositiveModifier, NegativeModifier}.
+
+-spec get_damage
+   (
+      precision(),
+      boolean(),
+      float(),
+      shr_omnimods:type(),
+      shr_omnimods:type()
+   )
+   -> non_neg_integer().
+get_damage
+(
+   Precision,
+   IsCritical,
+   StartingDamageMultiplier,
+   AttackerOmnimods,
+   DefenderOmnimods
+) ->
+   ActualDamageMultiplier =
+      (
+         StartingDamageMultiplier
+         *
+         (
+            case Precision of
+               misses -> 0;
+               grazes -> 0.5;
+               hits -> 1
+            end
+         )
+         *
+         (
+            case IsCritical of
+               true -> 2;
+               _ -> 1
+            end
+         )
+      ),
+
+   ActualDamage =
+      shr_omnimods:get_attack_damage
+      (
+         ActualDamageMultiplier,
+         AttackerOmnimods,
+         DefenderOmnimods
+      ),
+
+   ActualDamage.
+
+-spec get_character_abilities
+   (
+      btl_action:type(),
+      btl_character:type(),
+      btl_character:type()
+   )
+   -> {boolean(), boolean(), boolean()}.
+get_character_abilities (Action, Character, TargetCharacter) ->
+   CharacterWeapon =
+      shr_character:get_active_weapon
+      (
+         btl_character:get_base_character(Character)
+      ),
+
+   TargetCharacterWeapon =
+      shr_character:get_active_weapon
+      (
+         btl_character:get_base_character(TargetCharacter)
+      ),
+
+   DefenseRange = shr_weapon:get_minimum_range(CharacterWeapon),
+   AttackRange =  shr_weapon:get_maximum_range(CharacterWeapon),
+   TargetDefenseRange = shr_weapon:get_minimum_range(TargetCharacterWeapon),
+   TargetAttackRange =  shr_weapon:get_maximum_range(TargetCharacterWeapon),
+
+   IsNotOpportunistic = btl_action:get_is_opportunistic(Action),
+
+   AttackRange =
+      shr_location:dist
+      (
+         btl_character:get_location(Character),
+         btl_character:get_location(TargetCharacter)
+      ),
+
+   {
+      (DefenseRange == 0),
+      (
+         IsNotOpportunistic
+         and (TargetDefenseRange == 0)
+         and (TargetAttackRange =< AttackRange)
+      ),
+      (
+         IsNotOpportunistic
+         and (TargetAttackRange =< AttackRange)
+      )
+   }.
+
+-spec effect_of_attack
+   (
+      btl_attack:category(),
+      non_neg_integer(),
+      non_neg_integer(),
+      btl_character:type(),
+      btl_character:type(),
+      integer(),
+      integer(),
+      boolean(),
+      btl_character_turn_update:type()
+   )
+   ->
+   {
+      btl_character:type(),
+      btl_character:type(),
+      integer(),
+      integer(),
+      btl_character_turn_update:type(),
+      btl_attack:type()
+   }.
+effect_of_attack
+(
+   Category,
+   CharacterIX,
+   TargetCharacterIX,
+   S0Character,
+   S0TargetCharacter,
+   S0Luck,
+   S0TargetLuck,
+   TargetCanParry,
+   S0Update
+) ->
+   %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+   %%%% Roll parry to see if the roles have to be swapped. %%%%%%%%%%%%%%%%%%%%%
+
+   {ParryIsSuccessful, ParryPositiveLuckMod, ParryNegativeLuckMod} =
+      case TargetCanParry of
+         true ->
+            TargetStatistics =
+               shr_character:get_statistics
+               (
+                  btl_character:get_base_character(TargetCharacter)
+               ),
+            roll_parry(TargetStatistics, S0TargetLuck);
+
+         false -> {false, 0, 0}
+      end,
+
+   { AttackerIX, DefenderIX, Attacker, Defender, AttackerLuck, DefenderLuck } =
+      case ParryIsSuccessful of
+         true ->
+            {
+               TargetCharacterIX,
+               CharacterIX,
+               TargetCharacter,
+               Character,
+               TargetLuck,
+               Luck
+            };
+
+         false ->
+            {
+               CharacterIX,
+               TargetCharacterIX,
+               Character,
+               TargetCharacter,
+               Luck,
+               TargetLuck
+            }
+      end,
+
+   AttackerStatistics =
+
+-spec handle_attack_sequence
+   (
+      list({btl_attack:category(), boolean()}),
+      non_neg_integer(),
+      non_neg_integer(),
+      btl_character:type(),
+      btl_character:type(),
+      integer(),
+      integer(),
+      list(btl_attack:type()),
+      btl_character_turn_update:type()
+   )
+   ->
+   {
+      btl_character:type(),
+      btl_character:type(),
+      integer(),
+      integer(),
+      list(btl_attack:type()),
+      btl_character_turn_update:type()
+   }.
+handle_attack_sequence
+(
+   [],
+   _CharacterIX,
+   _TargetCharacterIX,
+   Character,
+   TargetCharacter,
+   PlayerLuck,
+   TargetPlayerLuck,
+   Results,
+   Update
+)
+->
+   {
+      Character,
+      TargetCharacter,
+      PlayerLuck,
+      TargetPlayerLuck,
+      lists:reverse(Results),
+      Update
+   };
+handle_attack_sequence
+(
+   [{first, TargetCanParry}|NextAttacks],
+   CharacterIX,
+   TargetCharacterIX,
+   S0Character,
+   S0TargetCharacter,
+   S0PlayerLuck,
+   S0TargetPlayerLuck,
+   Results,
+   S0Update
+)
+->
+   {
+      S1Character,
+      S1TargetCharacter,
+      S1PlayerLuck,
+      S1TargetPlayerLuck,
+      S1Update,
+      Result
+   } =
+      effect_of_attack
+      (
+         first,
+         CharacterIX,
+         TargetCharacterIX,
+         S0Character,
+         S0TargetCharacter,
+         S0PlayerLuck,
+         S0TargetPlayerLuck,
+         TargetCanParry,
+         S0Update
+      ),
+
+   handle_attack_sequence
+   (
+      NextAttacks,
+      CharacterIX,
+      TargetCharacterIX,
+      S1Character,
+      S1TargetCharacter,
+      S1PlayerLuck,
+      S1TargetPlayerLuck,
+      [Result|Results],
+      S1Update
+   );
+handle_attack_sequence
+(
+   [{counter, CanParry}|NextAttacks],
+   CharacterIX,
+   TargetCharacterIX,
+   S0Character,
+   S0TargetCharacter,
+   S0PlayerLuck,
+   S0TargetPlayerLuck,
+   Results,
+   S0Update
+)
+->
+   {
+      S1TargetCharacter,
+      S1Character,
+      S2TargetPlayerLuck,
+      S2PlayerLuck,
+      S1Update,
+      Result
+   } =
+      effect_of_attack
+      (
+         counter,
+         TargetCharacterIX,
+         CharacterIX,
+         S0TargetCharacter,
+         S0Character,
+         S1TargetPlayerLuck,
+         S1PlayerLuck,
+         CanParry,
+         S0Update
+      ),
+
+   handle_attack_sequence
+   (
+      NextAttacks,
+      CharacterIX,
+      TargetCharacterIX,
+      S1Character,
+      S1TargetCharacter,
+      S2PlayerLuck,
+      S2TargetPlayerLuck,
+      [Result|Results],
+      S1Update
+   );
+handle_attack_sequence
+(
+   [{second, TargetCanParry}|NextAttacks],
+   CharacterIX,
+   TargetCharacterIX,
+   S0Character,
+   S0TargetCharacter,
+   S0PlayerLuck,
+   S0TargetPlayerLuck,
+   Results,
+   S0Update
+)
+->
+   Statistics = shr_character:get_statistics(S0Character),
+   DoubleAttackChance = shr_statistics:get_double_hits(Statistics),
+   {_Roll, IsSuccessful, PositiveModifier, NegativeModifier} =
+      shr_roll:percentage_with_luck(DoubleAttackChance, S0PlayerLuck),
+
+   S1PlayerLuck = (S0PlayerLuck + PositiveModifier),
+   S1TargetPlayerLuck = (S0TargetPlayerLuck + NegativeModifier),
+
+   case IsSuccessful of
+      false ->
+         handle_attack_sequence
+         (
+            NextAttacks,
+            CharacterIX,
+            TargetCharacterIX,
+            S0Character,
+            S0TargetCharacter,
+            S1PlayerLuck,
+            S1TargetPlayerLuck,
+            Results,
+            S0Update
+         );
+
+      true ->
+         {
+            S1Character,
+            S1TargetCharacter,
+            S2PlayerLuck,
+            S2TargetPlayerLuck,
+            S1Update,
+            Result
+         } =
+            effect_of_attack
+            (
+               second,
+               CharacterIX,
+               TargetCharacterIX,
+               S0Character,
+               S0TargetCharacter,
+               S1PlayerLuck,
+               S1TargetPlayerLuck,
+               TargetCanParry,
+               S0Update
+            ),
+
+         handle_attack_sequence
+         (
+            CharacterIX,
+            TargetCharacterIX,
+            NextAttacks,
+            S1Character,
+            S1TargetCharacter,
+            S2PlayerLuck,
+            S2TargetPlayerLuck,
+            [Result|Results],
+            S1Update
+         )
+   end.
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%% EXPORTED FUNCTIONS %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+-spec handle
+   (
+      btl_action:type(),
+      btl_character:type(),
+      btl_character_turn_update:type()
+   )
+   -> {ok, btl_character_turn_update:type()}.
+handle (Action, S0Character, S0Update) ->
+   S0Battle = btl_character_turn_update:get_battle(S0Update),
+   CharacterIX = btl_action:get_actor_index(Action),
+
+   PlayerIX = btl_character:get_player_index(S0Character),
+   Player = btl_battle:get_player(PlayerIX, S0Battle),
+   S0PlayerLuck = btl_player:get_luck(Player),
+
+   TargetCharacterIX = btl_action:get_target_index(Action),
+   {S0TargetCharacter, S1Battle} =
+      btl_battle:get_resolved_character(TargetCharacterIX, S0Battle),
+
+   TargetPlayerIX = btl_character:get_player_index(TargetCharacter),
+   TargetPlayer = btl_battle:get_player(TargetPlayerIX, S1Battle),
+   TargetPlayerLuck = btl_player:get_luck(TargetPlayer),
+
+   {CanParry, TargetCanParry, TargetCanCounter} =
+      get_character_abilities(Action, S0Character, S0TargetCharacter),
+
+   {
+      S1Character,
+      S1TargetCharacter,
+      S1PlayerLuck,
+      S1TargetPlayerLuck,
+      Results,
+      S1Update
+   } =
+      handle_attack_sequence
+      (
+         case TargetCanCounter of
+            true ->
+               [
+                  {first, TargetCanParry},
+                  {counter, CanParry},
+                  {second, TargetCanParry}
+               ];
+
+            false ->
+               [
+                  {first, TargetCanParry},
+                  {second, TargetCanParry}
+               ]
+         end,
+         S1Character,
+         S1TargetCharacter,
+         S1PlayerLuck,
+         S1TargetPlayerLuck,
+         Results,
+         S1Update
+      ),
+
+   {
+      AttackEffects,
+      RemainingAttackerHealth,
+      RemainingDefenderHealth,
+      NewAttackerLuck,
+      NewDefenderLuck
+   } =
+      handle_attack_sequence
+      (
+         Character,
+         btl_character:get_current_health(Character),
+         TargetCharacter,
+         btl_character:get_current_health(TargetCharacter),
+         PlayerLuck,
+         TargetPlayerLuck,
+         AttackSequence,
+         []
+      ),
+
+   S0NewAttackerLuck =
+      case {(NewAttackerLuck =< -2), (NewAttackerLuck >= 2)}  of
+         {true, _} -> (NewAttackerLuck + 2);
+         {_, true} -> (NewAttackerLuck - 2);
+         _ -> 0
+      end,
+
+   S0NewDefenderLuck =
+      case {(NewDefenderLuck =< -2), (NewDefenderLuck >= 2)}  of
+         {true, _} -> (NewDefenderLuck + 2);
+         {_, true} -> (NewDefenderLuck - 2);
+         _ -> 0
+      end,
+
+   {UpdatedAttackingPlayer, AttackingPlayerAtaxiaUpdate} =
+      btl_player:ataxia_set_luck(S0NewAttackerLuck, AttackingPlayer),
+
+   {UpdatedDefendingPlayer, DefendingPlayerAtaxiaUpdate} =
+      btl_player:ataxia_set_luck(S0NewDefenderLuck, DefendingPlayer),
+
+   {UpdatedCharacter, CharacterAtaxiaUpdate} =
+      btl_character:ataxia_set_current_health
+      (
+         RemainingAttackerHealth,
+         Character
+      ),
+
+   {UpdatedTargetCharacterRef, TargetCharacterRefAtaxiaUpdate} =
+      btl_character:ataxia_set_current_health
+      (
+         RemainingDefenderHealth,
+         TargetCharacterRef
+      ),
+
+   {S0Battle, BattleAtaxiaUpdate0} =
+      btl_battle:ataxia_set_player
+      (
+         AttackingPlayerIX,
+         UpdatedAttackingPlayer,
+         AttackingPlayerAtaxiaUpdate,
+         Battle
+      ),
+
+   {S1Battle, BattleAtaxiaUpdate1} =
+      btl_battle:ataxia_set_player
+      (
+         DefendingPlayerIX,
+         UpdatedDefendingPlayer,
+         DefendingPlayerAtaxiaUpdate,
+         S0Battle
+      ),
+
+   {S2Battle, BattleAtaxiaUpdate2} =
+      btl_battle:ataxia_set_character
+      (
+         TargetIX,
+         UpdatedTargetCharacterRef,
+         TargetCharacterRefAtaxiaUpdate,
+         S1Battle
+      ),
+
+   % Potential danger ahead: we're going to update both the 'character' and
+   % 'battle' members of a btl_character_turn_update.
+   % 'S1Update' is sure to have both up to date (as it's the result of 'get'
+   % requests for both) and there is no risk of the 'battle' update influencing
+   % 'character', making what follows safe.
+
+   S2Update =
+      btl_character_turn_update:ataxia_set_battle
+      (
+         S2Battle,
+         false,
+         ataxic:optimize
+         (
+            ataxic:sequence
+            (
+               [
+                  BattleAtaxiaUpdate0,
+                  BattleAtaxiaUpdate1,
+                  BattleAtaxiaUpdate2
+               ]
+            )
+         ),
+         S1Update
+      ),
+
+   S3Update =
+      btl_character_turn_update:ataxia_set_character
+      (
+         UpdatedCharacter,
+         CharacterAtaxiaUpdate,
+         S2Update
+      ),
+
+   TimelineItem =
+      btl_turn_result:new_character_attacked
+      (
+         btl_character_turn_update:get_character_ix(S3Update),
+         TargetIX,
+         AttackEffects,
+         S0NewAttackerLuck,
+         S0NewDefenderLuck
+      ),
+
+   S4Update = btl_character_turn_update:add_to_timeline(TimelineItem, S3Update),
+
+   S5Update =
+      case (RemainingAttackerHealth > 0) of
+         true -> S4Update;
+         false ->
+            btl_victory_progression:handle_character_loss(Character, S4Update)
+      end,
+
+   S6Update =
+      case (RemainingDefenderHealth > 0) of
+         true -> S5Update;
+         false ->
+            btl_victory_progression:handle_character_loss
+            (
+               TargetCharacterRef,
+               S5Update
+            )
+      end,
+
+   {ok, S6Update}.
diff --git a/src/battle/mechanic/action/btl_action_move.erl b/src/battle/mechanic/action/btl_action_move.erl
new file mode 100644
index 0000000..a32a40f
--- /dev/null
+++ b/src/battle/mechanic/action/btl_action_move.erl
@@ -0,0 +1,291 @@
+-module(btl_action_move).
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%% TYPES %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%% EXPORTS %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+-export
+(
+   [
+      handle/3
+   ]
+).
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%% LOCAL FUNCTIONS %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+-spec cross
+   (
+      non_neg_integer(),
+      shr_map:type(),
+      list(shr_location:type()),
+      list(shr_direction:enum()),
+      non_neg_integer(),
+      shr_location:type()
+   )
+   ->
+   {
+      shr_location:type(),
+      list(shr_direction:type()),
+      non_neg_integer(),
+      list(shr_map_marker:type())
+   }.
+cross (_PlayerIX, _Map, _ForbiddenLocations, [], Cost, Location) ->
+   {Location, [], Cost, []};
+cross (PlayerIX, Map, ForbiddenLocations, [Step|NextSteps], Cost, Location) ->
+   NextLocation = shr_location:apply_direction(Step, Location),
+   NextTileInstance = shr_map:get_tile_instance(NextLocation, Map),
+   NextTileClassID = shr_tile_instance:get_tile_id(NextTileInstance),
+   NextTile = shr_tile:from_id(NextTileClassID),
+   NextCost = (Cost + shr_tile:get_cost(NextTile)),
+   IsForbidden =
+      lists:foldl
+      (
+         fun (ForbiddenLocation, Prev) ->
+            (Prev or (NextLocation == ForbiddenLocation))
+         end,
+         false,
+         ForbiddenLocations
+      ),
+
+   false = IsForbidden,
+
+   Interruptions =
+      list:foldl
+      (
+         fun (MarkerName, CurrentInterruptions) ->
+            case shr_map:get_marker(MarkerName, Map) of
+               {ok, Marker} ->
+                  case shr_map_marker:interrupts_movement(PlayerIX, Marker) of
+                     true -> [Marker|CurrentInterruptions];
+                     _ -> CurrentInterruptions
+                  end;
+
+               error ->
+                  %% TODO: Error.
+                  CurrentInterruptions
+            end
+         end,
+         [],
+         shr_tile_instance:get_triggers(NextTileInstance)
+      ),
+
+   case Interruptions of
+      [] ->
+         cross
+         (
+            PlayerIX,
+            Map,
+            ForbiddenLocations,
+            NextSteps,
+            NextCost,
+            NextLocation
+         );
+
+      _ -> {NextLocation, NextSteps, NextCost, Interruptions}
+   end.
+
+-spec cross
+   (
+      non_neg_integer(),
+      shr_map:type(),
+      list(shr_location:type()),
+      list(shr_direction:enum()),
+      shr_location:type()
+   )
+   ->
+   {
+      shr_location:type(),
+      list(shr_direction:type()),
+      non_neg_integer(),
+      list(shr_map_marker:type())
+   }.
+cross (PlayerIX, Map, ForbiddenLocations, Path, Location) ->
+   cross(PlayerIX, Map, ForbiddenLocations, Path, 0, Location).
+
+-spec get_path_cost_and_destination
+   (
+      non_neg_integer(),
+      btl_character:type(),
+      btl_character_turn_update:type(),
+      list(shr_direction:type())
+   )
+   ->
+   {
+      non_neg_integer(),
+      shr_location:type(),
+      list(shr_direction:type()),
+      list(shr_map_marker:type())
+   }.
+get_path_cost_and_destination (CharacterIX, Character, Update, Path) ->
+   Battle = btl_character_turn_update:get_battle(Update),
+   Map = btl_battle:get_map(Battle),
+
+   % [TODO][OPTIMIZATION] Redundant calculations.
+   % This is recalculated at every move action, despite there be no need
+   % to: The client will not allow the character to go somewhere that would
+   % only be freed because of an event.
+   ForbiddenLocations =
+      orddict:fold
+      (
+         fun (IX, Char, Prev) ->
+            IsAlive = btl_character:get_is_alive(Char),
+            if
+               (IX == CharacterIX) -> Prev;
+               (not IsAlive) -> Prev;
+               true ->
+                  ordsets:add_element(btl_character:get_location(Char), Prev)
+            end
+         end,
+         ordsets:new(),
+         btl_battle:get_characters(Battle)
+      ),
+
+   {NewLocation, RemainingPath, Cost, Interruptions} =
+      cross
+      (
+         btl_character:get_player_index(Character),
+         Map,
+         ForbiddenLocations,
+         Path,
+         btl_character:get_location(Character)
+      ),
+
+   {Cost, NewLocation, RemainingPath, Interruptions}.
+
+-spec get_movement_points
+   (
+      btl_action:type(),
+      btl_character:type()
+   )
+   -> non_neg_integer().
+get_movement_points (Action, Character) ->
+   case btl_action:get_movement_points(Action) of
+      -1 ->
+         shr_statistics:get_movement_points
+         (
+            shr_character:get_statistics
+            (
+               btl_character:get_base_character(Character)
+            )
+         );
+
+      Other -> Other
+   end.
+
+-spec commit_move
+   (
+      non_neg_integer(),
+      btl_character:type(),
+      btl_character_turn_update:type(),
+      list(shr_direction:type()),
+      shr_location:type()
+   )
+   -> btl_character_turn_update:type().
+commit_move (CharacterIX, Character, S0Update, Path, NewLocation) ->
+   S0Battle = btl_character_turn_update:get_battle(S0Update),
+
+   Map = btl_battle:get_map(S0Battle),
+
+   TileOmnimods =
+      shr_tile:get_omnimods
+      (
+         shr_tile:from_id
+         (
+            shr_tile_instance:get_tile_id
+            (
+               shr_map:get_tile_instance(NewLocation, Map)
+            )
+         )
+      ),
+
+   {UpdatedCharacter, CharacterAtaxiaUpdate} =
+      btl_character:ataxia_set_location(NewLocation, TileOmnimods, Character),
+
+   {UpdatedBattle, BattleAtaxiaUpdate} =
+      btl_battle:ataxia_set_character
+      (
+         CharacterIX,
+         UpdatedCharacter,
+         CharacterAtaxiaUpdate,
+         S0Battle
+      ),
+
+   TimelineItem =
+      btl_turn_result:new_character_moved(CharacterIX, Path, NewLocation),
+
+   S1Update = btl_character_turn_update:add_to_timeline(TimelineItem, S0Update),
+   S2Update =
+      btl_character_turn_update:ataxia_set_battle
+      (
+         UpdatedBattle,
+         BattleAtaxiaUpdate,
+         S1Update
+      ),
+
+   S2Update.
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%% EXPORTED FUNCTIONS %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+-spec handle
+   (
+      btl_action:type(),
+      btl_character:type(),
+      btl_character_turn_update:type()
+   )
+   ->
+   (
+      {'ok', btl_character_turn_update:type()}
+      | {'events', list(btl_action:type()), btl_character_turn_update:type()}
+   ).
+handle (Action, Character, S0Update) ->
+   Path = btl_action:get_path(Action),
+   CharacterIX = btl_action:get_actor_index(Action),
+
+   {PathCost, NewLocation, RemainingPath, Interruptions} =
+      get_path_cost_and_destination(CharacterIX, Character, S0Update, Path),
+
+   MovementPoints = get_movement_points(Action, Character),
+
+   true = (MovementPoints >= PathCost),
+
+   S1Update = commit_move(CharacterIX, Character, S0Update, Path, NewLocation),
+
+   case RemainingPath of
+      [] -> {ok, S1Update};
+      _ ->
+         {events,
+            (
+               lists:foldl
+               (
+                  fun (Marker, CurrentActions) ->
+                     (
+                        btl_action:from_map_marker
+                        (
+                           CharacterIX,
+                           Character,
+                           Marker
+                        )
+                        ++
+                        CurrentActions
+                     )
+                  end,
+                  [],
+                  Interruptions
+               )
+               ++
+               [
+                  btl_action:new_move
+                  (
+                     CharacterIX,
+                     RemainingPath,
+                     (MovementPoints - PathCost)
+                  )
+               ]
+            ),
+            S1Update
+         }
+   end.
diff --git a/src/battle/mechanic/action/btl_action_switch_weapon.erl b/src/battle/mechanic/action/btl_action_switch_weapon.erl
new file mode 100644
index 0000000..cf1a31a
--- /dev/null
+++ b/src/battle/mechanic/action/btl_action_switch_weapon.erl
@@ -0,0 +1,66 @@
+-module(btl_turn_actions_switch_weapon).
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%% TYPES %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%% EXPORTS %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+-export
+(
+   [
+      handle/3
+   ]
+).
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%% LOCAL FUNCTIONS %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%% EXPORTED FUNCTIONS %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+-spec handle
+   (
+      btl_action:type(),
+      btl_character:type(),
+      btl_character_turn_update:type()
+   )
+   -> {'ok', btl_character_turn_update:type()}.
+handle (Action, Character, S0Update) ->
+   CharacterIX = btl_action:get_actor_index(Action),
+
+   BaseCharacter = btl_character:get_base_character(Character),
+
+   {UpdatedBaseCharacter, BaseCharacterAtaxiaUpdate} =
+      shr_character:ataxia_switch_weapons(BaseCharacter),
+
+   {UpdatedCharacter, CharacterAtaxiaUpdate} =
+      btl_character:ataxia_set_base_character
+      (
+         UpdatedBaseCharacter,
+         BaseCharacterAtaxiaUpdate,
+         Character
+      ),
+
+   {UpdatedBattle, BattleAtaxiaUpdate} =
+      btl_battle:ataxia_set_character
+      (
+         CharacterIX,
+         UpdatedCharacter,
+         CharacterAtaxiaUpdate,
+         btl_character_turn_update:get_battle(S0Update)
+      ),
+
+   TimelineItem = btl_turn_result:new_character_switched_weapons(CharacterIX),
+
+   S1Update = btl_character_turn_update:add_to_timeline(TimelineItem, S0Update),
+   S2Update =
+      btl_character_turn_update:ataxia_set_battle
+      (
+         UpdatedBattle,
+         BattleAtaxiaUpdate,
+         S1Update
+      ),
+
+   {ok, S2Update}.
diff --git a/src/battle/mechanic/action/btl_turn_actions_opportunity_attack.erl b/src/battle/mechanic/action/btl_turn_actions_opportunity_attack.erl
new file mode 100644
index 0000000..c1dbbdd
--- /dev/null
+++ b/src/battle/mechanic/action/btl_turn_actions_opportunity_attack.erl
@@ -0,0 +1,178 @@
+-module(btl_turn_actions_opportunity_attack).
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%% TYPES %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%% EXPORTS %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+-export
+(
+   [
+      handle/2
+   ]
+).
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%% LOCAL FUNCTIONS %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%% EXPORTED FUNCTIONS %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+-spec handle
+   (
+      btl_action:type(),
+      btl_character_turn_update:type()
+   )
+   -> {ok, btl_character_turn_update:type()}.
+handle (BattleAction, Update) ->
+   {S0Update, Battle} = btl_character_turn_update:get_battle(Update),
+   {S1Update, Character} = btl_character_turn_update:get_character(S0Update),
+
+   DefendingPlayerIX = btl_character:get_player_index(Character),
+   DefendingPlayer = btl_battle:get_player(DefendingPlayerIX, Battle),
+   DefendingPlayerLuck = btl_player:get_luck(DefendingPlayer),
+
+   AttackerIX = btl_action:get_target_ix(BattleAction),
+   AttackerRef = btl_battle:get_character(AttackerIX, Battle),
+   Attacker = btl_battle:resolve_character(AttackerRef, Battle),
+
+   AttackingPlayerIX = btl_character:get_player_index(Attacker),
+   AttackingPlayer = btl_battle:get_player(AttackingPlayerIX, Battle),
+   AttackingPlayerLuck = btl_player:get_luck(AttackingPlayer),
+
+   Attack = btl_attack:attack_of_opportunity(),
+
+   AttackEffect =
+      btl_attack:get_description_of
+      (
+         Attack,
+         btl_character:get_base_character(Character),
+         btl_character:get_base_character(Attacker),
+         AttackingPlayerLuck,
+         DefendingPlayerLuck
+      ),
+
+   {
+      AttackResult,
+      NewAttackerHealth,
+      S0NewAttackerLuck,
+      NewDefenderHealth,
+      S0NewDefenderLuck
+   } =
+      btl_attack:apply_to_healths_and_lucks
+      (
+         AttackEffect,
+         btl_character:get_current_health(Attacker),
+         AttackingPlayerLuck,
+         btl_character:get_current_health(Character),
+         DefendingPlayerLuck
+      ),
+
+   S1NewAttackerLuck =
+      case {(S0NewAttackerLuck =< -2), (S0NewAttackerLuck >= 2)}  of
+         {true, _} -> (S0NewAttackerLuck + 2);
+         {_, true} -> (S0NewAttackerLuck - 2);
+         _ -> 0
+      end,
+
+   S1NewDefenderLuck =
+      case {(S0NewDefenderLuck =< -2), (S0NewDefenderLuck >= 2)}  of
+         {true, _} -> (S0NewDefenderLuck + 2);
+         {_, true} -> (S0NewDefenderLuck - 2);
+         _ -> 0
+      end,
+
+   {UpdatedAttackingPlayer, AttackingPlayerAtaxiaUpdate} =
+      btl_player:ataxia_set_luck(S1NewAttackerLuck, AttackingPlayer),
+
+   {UpdatedDefendingPlayer, DefendingPlayerAtaxiaUpdate} =
+      btl_player:ataxia_set_luck(S1NewDefenderLuck, DefendingPlayer),
+
+   {UpdatedCharacter, CharacterAtaxiaUpdate} =
+      btl_character:ataxia_set_current_health(NewDefenderHealth, Character),
+
+   {UpdatedAttackerRef, AttackerRefAtaxiaUpdate} =
+      btl_character:ataxia_set_current_health(NewAttackerHealth, AttackerRef),
+
+   {S0Battle, BattleAtaxiaUpdate0} =
+      btl_battle:ataxia_set_player
+      (
+         AttackingPlayerIX,
+         UpdatedAttackingPlayer,
+         AttackingPlayerAtaxiaUpdate,
+         Battle
+      ),
+
+   {S1Battle, BattleAtaxiaUpdate1} =
+      btl_battle:ataxia_set_player
+      (
+         DefendingPlayerIX,
+         UpdatedDefendingPlayer,
+         DefendingPlayerAtaxiaUpdate,
+         S0Battle
+      ),
+
+   {S2Battle, BattleAtaxiaUpdate2} =
+      btl_battle:ataxia_set_character
+      (
+         AttackerIX,
+         UpdatedAttackerRef,
+         AttackerRefAtaxiaUpdate,
+         S1Battle
+      ),
+
+   % Potential danger ahead: we're going to update both the 'character' and
+   % 'battle' members of a btl_character_turn_update.
+   % 'S1Update' is sure to have both up to date (as it's the result of 'get'
+   % requests for both) and there is no risk of the 'battle' update influencing
+   % 'character', making what follows safe.
+
+   S2Update =
+      btl_character_turn_update:ataxia_set_battle
+      (
+         S2Battle,
+         false,
+         ataxic:optimize
+         (
+            ataxic:sequence
+            (
+               [
+                  BattleAtaxiaUpdate0,
+                  BattleAtaxiaUpdate1,
+                  BattleAtaxiaUpdate2
+               ]
+            )
+         ),
+         S1Update
+      ),
+
+   S3Update =
+      btl_character_turn_update:ataxia_set_character
+      (
+         UpdatedCharacter,
+         CharacterAtaxiaUpdate,
+         S2Update
+      ),
+
+   TimelineItem =
+      btl_turn_result:new_character_attacked
+      (
+         AttackerIX,
+         btl_character_turn_update:get_character_ix(S3Update),
+         AttackResult,
+         S0NewAttackerLuck,
+         S0NewDefenderLuck
+      ),
+
+   S4Update = btl_character_turn_update:add_to_timeline(TimelineItem, S3Update),
+
+   S5Update =
+      case (NewDefenderHealth > 0) of
+         true -> S4Update;
+         false ->
+            btl_victory_progression:handle_character_loss(Character, S4Update)
+      end,
+
+   {ok, S5Update}.