fix(combat): correct hex and AoE DCs, DR bypassed by spells

src/pf1e_simulator/combat.py

@@ -1260,7 +1260,7 @@ class CombatEngine:
             )
             return
 
-        hex_dc = 10 + state.combatant.level // 2 + (state.combatant.abilities.cha_score - 10) // 2
+        hex_dc = 10 + state.combatant.level // 2 + (state.combatant.abilities.int_score - 10) // 2
 
         if hex_name == "evil_eye":
             self._hex_evil_eye(state, target, hex_dc)
@@ -1519,6 +1519,7 @@ class CombatEngine:
             caster=caster, spell_name=spell.name,
             empower="Empower Spell" in metamagic_feats,
             maximize="Maximize Spell" in metamagic_feats,
+            dc=dc,
         )
         save_str = _save_label(save_result)
         self._log(
@@ -1559,6 +1560,7 @@ class CombatEngine:
         spell_name: str,
         empower: bool = False,
         maximize: bool = False,
+        dc: int = 15,
     ) -> list[str]:
         saved = save_result is not None and save_result.success
         return [
@@ -1566,6 +1568,7 @@ class CombatEngine:
                 effect, target, caster_live, target_live,
                 caster=caster, spell_name=spell_name,
                 empower=empower, maximize=maximize, saved=saved,
+                dc=dc,
             )
             for effect in effects
         ]
@@ -1582,12 +1585,13 @@ class CombatEngine:
         empower: bool = False,
         maximize: bool = False,
         saved: bool,
+        dc: int = 15,
     ) -> str:
         if isinstance(effect, AreaEffect):
             return self._apply_area_effect(
                 effect, target, caster_live, target_live,
                 caster=caster, spell_name=spell_name, saved=saved,
-                empower=empower, maximize=maximize,
+                empower=empower, maximize=maximize, dc=dc,
             )
         if isinstance(effect, SummonEffect):
             return self._apply_summon_effect(effect, caster, caster_live, spell_name)
@@ -1619,7 +1623,6 @@ class CombatEngine:
         dmg = max(0, raw // 2) if saved and effect.half_on_save else raw
         if empower:
             dmg = int(dmg * 1.5)
-        dmg = self._apply_dr_for_types(dmg, frozenset(effect.types), target)
         target.hp -= dmg
         caster_live.damage_dealt += dmg
         target_live.damage_taken += dmg
@@ -1691,6 +1694,7 @@ class CombatEngine:
         saved: bool,
         empower: bool = False,
         maximize: bool = False,
+        dc: int = 15,
     ) -> str:
         """Apply an area effect to all creatures within radius.
 
@@ -1709,7 +1713,7 @@ class CombatEngine:
 
         for affected_state in affected:
             creature_saved = self._area_save(
-                affected_state, target, effect, saved=saved
+                affected_state, target, effect, saved=saved, dc=dc
             )
             for sub_effect in effect.effects:
                 target_live = self._stats[affected_state.combatant.id]
@@ -1751,13 +1755,14 @@ class CombatEngine:
         effect: AreaEffect,
         *,
         saved: bool,
+        dc: int = 15,
     ) -> bool:
         """Save result for one creature in an area effect."""
         if not effect.save_for_half:
             return False
         if affected_state is target:
             return saved
-        save_result = self.resolve_save(affected_state, "ref", 15)
+        save_result = self.resolve_save(affected_state, "ref", dc)
         return save_result.success
 
     def _apply_metamagic(

tests/test_hex_aoe_dr.py

@@ -0,0 +1,162 @@
+"""Tests for hex DC, AoE save DC, and spell damage DR bypass (Task 5)."""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+from pf1e_simulator.combat import CombatantState, CombatEngine
+from pf1e_simulator.dice import parse_dice
+from pf1e_simulator.grid import Grid
+from pf1e_simulator.map import MapSpec, TerrainType
+from pf1e_simulator.models import (
+    AbilityScores,
+    ACProfile,
+    AttackSpec,
+    Combatant,
+    DamageComponent,
+    DamageReduction,
+    Saves,
+)
+from pf1e_simulator.rng import ScriptedRng
+from pf1e_simulator.spells import load_spell_registry
+
+_SPELLS_DIR = Path(__file__).resolve().parent.parent / "data" / "spells"
+
+
+def _make_caster(cid: str = "caster", *, level: int = 5, int_score: int = 18) -> Combatant:
+    attack = AttackSpec(
+        id=f"{cid}-w",
+        name="dagger",
+        kind="melee",
+        attack_bonus=2,
+        damage=[DamageComponent(formula=parse_dice("1d4"), types=["piercing"])],
+    )
+    return Combatant(
+        id=cid,
+        name=cid,
+        level=level,
+        size="Medium",
+        abilities=AbilityScores(
+            str_score=10, dex_score=14, con_score=12,
+            int_score=int_score, wis_score=12, cha_score=10,
+        ),
+        hp_max=20,
+        ac=ACProfile(total=12, touch=12, flat_footed=10),
+        bab=2,
+        initiative_mod=2,
+        speed_land_ft=30,
+        saves=Saves(fort=3, ref=4, will=4),
+        attacks=[attack],
+        casting_ability="int",
+        spell_slots={1: 4, 2: 3, 3: 2},
+        resources={"hexes": 3, "channel_energy": 6},
+    )
+
+
+def _make_target(cid: str = "target", *, hp_max: int = 30) -> Combatant:
+    attack = AttackSpec(
+        id=f"{cid}-w",
+        name="club",
+        kind="melee",
+        attack_bonus=3,
+        damage=[DamageComponent(formula=parse_dice("1d6"), types=["bludgeoning"])],
+    )
+    return Combatant(
+        id=cid,
+        name=cid,
+        level=1,
+        size="Medium",
+        abilities=AbilityScores(
+            str_score=10, dex_score=10, con_score=10,
+            int_score=10, wis_score=10, cha_score=10,
+        ),
+        hp_max=hp_max,
+        ac=ACProfile(total=10, touch=10, flat_footed=10),
+        bab=1,
+        initiative_mod=0,
+        speed_land_ft=30,
+        saves=Saves(fort=2, ref=2, will=2),
+        attacks=[attack],
+    )
+
+
+def _make_engine(
+    caster: Combatant,
+    target: Combatant,
+    queue: list[int],
+    *,
+    caster_pos: tuple[int, int] = (0, 0),
+    target_pos: tuple[int, int] = (3, 0),
+) -> tuple[CombatEngine, CombatantState, CombatantState]:
+    c = CombatantState(
+        combatant=caster, side="players", pos=caster_pos, hp=caster.hp_max,
+        resources_left=dict(caster.resources),
+    )
+    t = CombatantState(
+        combatant=target, side="monsters", pos=target_pos, hp=target.hp_max,
+        resources_left=dict(target.resources),
+    )
+    legend = {".": TerrainType(type="floor", move_cost=1)}
+    spec = MapSpec(name="test", terrain=tuple(["." * 12] * 12), legend=legend)
+    grid = Grid.from_spec(spec)
+    reg = load_spell_registry(_SPELLS_DIR)
+    engine = CombatEngine(ScriptedRng(queue), grid, [c, t], spell_registry=reg)
+    return engine, c, t
+
+
+class TestHexDcUsesInt:
+    """Given: a witch with level 4, INT 21 (mod +5)
+    When: evil_eye hex is cast (Will save)
+    Then: DC = 10 + 4//2 + (21-10)//2 = 17.
+
+    Behavioral test: target has Will +2. d20=13 -> total 15.
+    DC 17: 15 < 17 -> fail -> shaken applied.
+    DC 12 (wrong, uses CHA): 15 >= 12 -> success -> no effect.
+    """
+
+    def test_hex_dc_uses_int_not_cha(self) -> None:
+        caster = _make_caster(level=4, int_score=21)
+        target = _make_target(hp_max=100)
+        engine, c, t = _make_engine(caster, target, [13])
+        engine._execute_hex(c, t, "evil_eye")
+        assert any("shaken" in line for line in engine._transcript)
+
+
+class TestAoEDcEqualsCasterSpellDc:
+    """Given: a caster with INT 18 (mod +4) casting Fireball (level 3)
+    When: the AoE targets a secondary creature (caster self in area)
+    Then: the area save DC equals the caster's spell DC (17), not hardcoded 15.
+
+    Behavioral test: secondary target (caster) has ref +4.
+    d20=12 -> total 12+4=16. DC 17 -> 16<17 -> fail (full damage).
+    If DC 15 (old bug): 16>=15 -> success (half damage).
+    """
+
+    def test_area_save_uses_caster_dc(self) -> None:
+        caster = _make_caster(level=5, int_score=18)
+        target = _make_target(hp_max=200)
+        queue = [1, 12, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3]
+        engine, c, t = _make_engine(caster, target, queue)
+        hp_before_caster = c.hp
+        hp_before_target = t.hp
+        engine._cast_spell(c, t, "Fireball")
+        assert t.hp == hp_before_target - 18
+        assert c.hp == hp_before_caster - 18
+
+
+class TestSpellDamageBypassesDr:
+    """Given: a target with DR 5/- (bypassed by nothing)
+    When: a spell deals fire damage
+    Then: DR does NOT reduce spell damage (PF1e: spells/energy bypass DR)."""
+
+    def test_dr_does_not_reduce_spell_damage(self) -> None:
+        caster = _make_caster(level=5, int_score=18)
+        target = _make_target(hp_max=200)
+        target_with_dr = target.model_copy(update={
+            "dr": DamageReduction(amount=5, bypass=frozenset()),
+        })
+        queue = [2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3]
+        engine, c, t = _make_engine(caster, target_with_dr, queue)
+        hp_before = t.hp
+        engine._cast_spell(c, t, "Fireball")
+        assert t.hp == hp_before - 18

tests/test_spells.py

@@ -395,14 +395,14 @@ class TestSpellDcScalesWithLevel:
 
 
 class TestSpellDamageWithDr:
-    """Given: a target with DR vs the spell's damage type
+    """Given: a target with DR 5/- (bypassed by nothing)
     When: a spell deals damage
-    Then: DR is applied after save halving."""
+    Then: DR does NOT reduce spell damage (PF1e: spells/energy bypass DR)."""
 
-    def test_dr_reduces_spell_damage(self) -> None:
+    def test_dr_does_not_reduce_spell_damage(self) -> None:
         caster = _make_caster()
         target = _make_target(hp_max=200)
-        # DR 5/- (bypassed by nothing) applies to all damage including fire
+        # DR 5/- does NOT apply to spell damage
         target_with_dr = target.model_copy(update={
             "dr": DamageReduction(amount=5, bypass=frozenset()),
         })
@@ -411,8 +411,8 @@ class TestSpellDamageWithDr:
         engine, c, t = _make_engine(caster, target_with_dr, queue)
         hp_before = t.hp
         engine._cast_spell(c, t, "Fireball")
-        # Save fails (2), 6d6 rolls all 3 = 18 damage, DR 5/- -> 13 damage
+        # Save fails (2), 6d6 rolls all 3 = 18 damage, DR ignored -> 18 damage
-        assert t.hp == hp_before - 13
+        assert t.hp == hp_before - 18
 
 
 class TestSummonMonster: