feat(combat): support variable melee reach for weapons and creature size

src/pf1e_simulator/combat.py

@@ -138,6 +138,17 @@ _SIZE_MODIFIERS: dict[str, int] = {
     "medium": 0, "large": 1, "huge": 2, "gargantuan": 4, "colossal": 8,
 }
 
+# PF1e natural reach for tall creatures (simplification: no long/quadruped
+# distinction). Unknown sizes fall back to 5 ft (the historical behavior).
+_SIZE_NATURAL_REACH_FT: dict[str, int] = {
+    "Small": 5,
+    "Medium": 5,
+    "Large": 10,
+    "Huge": 15,
+    "Gargantuan": 20,
+    "Colossal": 30,
+}
+
 # Row-major scan order of the 8 adjacent cells, used by reposition.
 _NEIGHBOR_OFFSETS: tuple[tuple[int, int], ...] = (
     (-1, -1), (-1, 0), (-1, 1), (0, -1), (0, 1), (1, -1), (1, 0), (1, 1),
@@ -162,6 +173,11 @@ _STEP_DELTAS: tuple[Pos, ...] = (
 )
 
 
+def _effective_reach_ft(state: CombatantState, weapon: AttackSpec) -> int:
+    """Effective melee reach in feet: max of natural size reach and weapon reach."""
+    return max(_SIZE_NATURAL_REACH_FT.get(state.combatant.size, 5), weapon.reach_ft)
+
+
 def _bresenham_line(start: Pos, end: Pos) -> list[Pos]:
     """Integer Bresenham line from start to end (exclusive of start, inclusive of end)."""
     r0, c0 = start
@@ -547,8 +563,13 @@ class CombatEngine:
             return None
         dist_ft = self._grid.distance(attacker.pos, target.pos) * _SQUARE_FT
         for weapon in attacker.usable_attacks():
-            if weapon.kind in ("melee", "touch") and dist_ft <= weapon.reach_ft:
-                return weapon
+            if weapon.kind in ("melee", "touch"):
+                effective_reach_ft = _effective_reach_ft(attacker, weapon)
+                if weapon.reach_ft > _SQUARE_FT:
+                    if _SQUARE_FT < dist_ft <= effective_reach_ft:
+                        return weapon
+                elif dist_ft <= effective_reach_ft:
+                    return weapon
             max_increments = (
                 _MAX_TOUCH_RANGE_INCREMENTS
                 if weapon.kind == "touch"
@@ -964,13 +985,42 @@ class CombatEngine:
         return None
 
     def _threatened_squares(self, state: CombatantState) -> frozenset[Pos]:
-        """Squares this combatant threatens with a melee weapon (8 adjacent for 5 ft reach)."""
+        """Squares this combatant threatens with a melee weapon.
+
+        Non-reach weapons (reach_ft == 5) threaten the disk of effective reach;
+        reach weapons (reach_ft > 5) threaten only the ring at exactly their
+        reach (PF1e reach dead zone). The union over usable melee weapons is
+        returned.
+        """
         if not state.active:
             return frozenset()
-        if not any(w.kind == "melee" for w in state.usable_attacks()):
+        melee = [w for w in state.usable_attacks() if w.kind == "melee"]
+        if not melee:
             return frozenset()
+        threatened: set[Pos] = set()
+        for weapon in melee:
+            threatened |= self._weapon_threatened_squares(state, weapon)
+        return frozenset(threatened)
+
+    def _weapon_threatened_squares(self, state: CombatantState, weapon: AttackSpec) -> set[Pos]:
+        """Squares one melee weapon threatens: disk for non-reach, ring for reach."""
         r, c = state.pos
-        return frozenset((r + dr, c + dc) for dr, dc in _STEP_DELTAS)
+        threatened: set[Pos] = set()
+        if weapon.reach_ft > _SQUARE_FT:
+            ring = weapon.reach_ft // _SQUARE_FT
+            for dr in range(-ring, ring + 1):
+                for dc in range(-ring, ring + 1):
+                    if self._grid.distance(state.pos, (r + dr, c + dc)) == ring:
+                        threatened.add((r + dr, c + dc))
+        else:
+            reach_cells = _effective_reach_ft(state, weapon) // _SQUARE_FT
+            for dr in range(-reach_cells, reach_cells + 1):
+                for dc in range(-reach_cells, reach_cells + 1):
+                    if (dr, dc) == (0, 0):
+                        continue
+                    if self._grid.distance(state.pos, (r + dr, c + dc)) <= reach_cells:
+                        threatened.add((r + dr, c + dc))
+        return threatened
 
     def _enemies_threatening(self, state: CombatantState, pos: Pos) -> list[CombatantState]:
         """Active enemies whose threatened squares include pos (in self._states order)."""
@@ -1111,8 +1161,11 @@ class CombatEngine:
         for weapon in state.usable_attacks():
             if weapon.kind != "melee":
                 continue
-            reach_cells = weapon.reach_ft // _SQUARE_FT
-            end = self._charge_end(state, target, reach_cells, max_cells, blocked)
+            reach_cells = _effective_reach_ft(state, weapon) // _SQUARE_FT
+            min_reach_cells = weapon.reach_ft // _SQUARE_FT if weapon.reach_ft > _SQUARE_FT else 0
+            end = self._charge_end(
+                state, target, reach_cells, max_cells, blocked, min_reach_cells=min_reach_cells
+            )
             if end is not None:
                 return weapon
         return None
@@ -1124,6 +1177,8 @@ class CombatEngine:
         reach_cells: int,
         max_cells: int,
         blocked: frozenset[Pos],
+        *,
+        min_reach_cells: int = 0,
     ) -> Pos | None:
         """Find the closest square from which ``state`` can melee ``target`` via a charge.
 
@@ -1133,7 +1188,9 @@ class CombatEngine:
         Ties break toward lower distance from state.
         """
         candidates: list[tuple[int, Pos]] = []
-        for end in self._charge_candidates(target, reach_cells, blocked, state.pos):
+        for end in self._charge_candidates(
+            target, reach_cells, blocked, state.pos, min_reach_cells
+        ):
             path = _bresenham_line(state.pos, end)
             if len(path) < _CHARGE_MIN_CELLS or len(path) > max_cells:
                 continue
@@ -1151,6 +1208,7 @@ class CombatEngine:
         reach_cells: int,
         blocked: frozenset[Pos],
         start: Pos,
+        min_reach_cells: int = 0,
     ) -> list[Pos]:
         """Squares within reach of target, passable, unoccupied, not the start."""
         tr, tc = target.pos
@@ -1168,7 +1226,8 @@ class CombatEngine:
                     continue
                 if end in blocked:
                     continue
-                if self._grid.distance(end, target.pos) > reach_cells:
+                dist = self._grid.distance(end, target.pos)
+                if dist > reach_cells or dist < min_reach_cells:
                     continue
                 result.append(end)
         return result
@@ -1194,13 +1253,16 @@ class CombatEngine:
         (cleared in ``_take_turn``). Movement during a charge provokes AoOs step-by-step
         as for any move action.
         """
-        reach_cells = weapon.reach_ft // _SQUARE_FT
+        reach_cells = _effective_reach_ft(attacker, weapon) // _SQUARE_FT
+        min_reach_cells = weapon.reach_ft // _SQUARE_FT if weapon.reach_ft > _SQUARE_FT else 0
         speed_cells = attacker.combatant.speed_land_ft // _SQUARE_FT
         max_cells = 2 * speed_cells
         blocked = frozenset(
             s.pos for s in self._states if s is not attacker and s is not target and s.active
         )
-        end = self._charge_end(attacker, target, reach_cells, max_cells, blocked)
+        end = self._charge_end(
+            attacker, target, reach_cells, max_cells, blocked, min_reach_cells=min_reach_cells
+        )
         if end is None:
             return
         path = _bresenham_line(attacker.pos, end)