feat(combat): add concealment miss chance, sneak attack, and Precise Shot

src/pf1e_simulator/combat.py

@@ -138,6 +138,11 @@ _CHARGE_MIN_CELLS = 2  # PF1e: charge must move at least 10 ft (2 squares)
 _UP_CLOSE_RANGE_FT = 30  # PF1e: Up Close and Deadly works within 30 ft
 # PF1e: Point-Blank Shot grants +1/+1 within 30 ft with ranged weapons
 _POINT_BLANK_RANGE_FT = 30
+_FIRING_MELEE_PENALTY = -4  # PF1e: ranged attack into melee
+_FIRING_MELEE_REDUCED_PENALTY = -2  # PF1e: -2 when the melee is 10+ ft away
+_FIRING_MELEE_SAFE_FT = 10  # PF1e: 2 cells (10 ft) from attacker = reduced penalty
+_SNEAK_ATTACK_FEATURE = "Sneak Attack"  # PF1e: rogue class feature (precision dice)
+_PRECISE_SHOT_FEATURE = "Precise Shot"  # PF1e: feat negating firing-into-melee penalty
 _SAVE_DESCRIPTOR_CONDITIONS = frozenset({
     "fear", "cold", "electricity", "fey", "divination", "poison", "disease",
     "mind_affecting",
@@ -236,6 +241,7 @@ def _condition_definition_dict(cond: Condition) -> dict[str, object]:
         "mods": [_stat_modifier_dict(m) for m in cond.modifiers],
         "flags": flags,
         "speed_mult": cond.speed_mult,
+        "miss_chance": cond.miss_chance,
     }
 
 
@@ -395,6 +401,7 @@ class AttackResult:
     flank_bonus: int = 0
     high_ground_bonus: int = 0
     base_bonus: int = 0
+    melee_penalty: int = 0
 
 
 @dataclass(frozen=True)
@@ -845,6 +852,12 @@ class CombatEngine:
             "spell_resistance": state.combatant.spell_resistance,
             "resistances": dict(state.combatant.resistances),
             "immunities": tuple(state.combatant.immunities),
+            "sneak_dice": (
+                (state.combatant.level + 1) // 2
+                if self._has_feat(state, _SNEAK_ATTACK_FEATURE)
+                else 0
+            ),
+            "engaged_in_melee": self._engaged_in_melee(state),
         }
 
     def _pair_snapshot(
@@ -1311,6 +1324,11 @@ class CombatEngine:
             else 0
         )
         base_bonus = bonus_override if bonus_override is not None else weapon.attack_bonus
+        fim_penalty = (
+            self._firing_into_melee_penalty(attacker, target)
+            if self._is_ranged_attack(weapon)
+            else 0
+        )
         atk_mods = self._stat_modifiers(
             attacker, "attack", weapon_name=weapon.name, weapon=weapon, dist_ft=dist_ft
         )
@@ -1318,7 +1336,10 @@ class CombatEngine:
             atk_mods.append(StatModifier(target="attack", value=-4))
         attack_mod = resolve_modifiers(atk_mods)
         pa_amt = self._power_attack_amt(attacker) if weapon.kind == "melee" else 0
-        total = roll + base_bonus + penalty + flank + high_ground + attack_mod - pa_amt
+        total = (
+            roll + base_bonus + penalty + flank + high_ground + attack_mod - pa_amt
+            + fim_penalty
+        )
         # Check if target denies DEX to AC (flat-footed)
         denies_dex = self.has_condition_flag(target, "denies_dex_to_ac")
         full_ac_base = (
@@ -1358,38 +1379,173 @@ class CombatEngine:
         ):
             ac += _COVER_AC_BONUS
         hit = roll == _NATURAL_TWENTY or (roll != _NATURAL_ONE and total >= ac)
-        crit = False
         damage = 0
+        concealment_miss = False
+        crit = False
         if hit:
-            if roll != _NATURAL_ONE and roll >= weapon.crit_range:
-                confirm = self._rng.d20()
-                confirm_total = (
-                    confirm + base_bonus + penalty + flank + high_ground + attack_mod - pa_amt
-                )
-                crit = confirm != _NATURAL_ONE and confirm_total >= ac
-            dmg_mods = self._stat_modifiers(
-                attacker, "damage", weapon_name=weapon.name, weapon=weapon, dist_ft=dist_ft
+            crit, concealment_miss, damage = self._resolve_hit_damage(
+                attacker, target, weapon, roll=roll, ac=ac, base_bonus=base_bonus,
+                penalty=penalty, flank=flank, high_ground=high_ground,
+                attack_mod=attack_mod, pa_amt=pa_amt, fim_penalty=fim_penalty,
+                dist_ft=dist_ft, denies_dex=denies_dex,
             )
-            damage = sum(c.formula.roll(self._rng) for c in weapon.damage) + weapon.damage_bonus
-            damage += resolve_modifiers(dmg_mods)
-            damage += pa_amt * 2 if weapon.kind == "melee" else 0
-            if crit:
-                damage *= weapon.crit_mult
-            damage = self._apply_dr(damage, weapon, target)
-            weapon_types = frozenset(
-                t for comp in weapon.damage for t in comp.types
+        if not concealment_miss:
+            target.hp -= damage
+            damage = self._consume_up_close_and_deadly(
+                attacker, target, weapon, dist_ft, damage, hit=hit
             )
-            damage = self._apply_energy_resistance(
-                damage, weapon_types, target
-            )
-        target.hp -= damage
-        damage = self._consume_up_close_and_deadly(
-            attacker, target, weapon, dist_ft, damage, hit=hit
-        )
         return AttackResult(
             hit=hit, crit=crit, damage=damage, roll=roll, total=total, ac=ac,
             penalty=penalty, flank_bonus=flank, high_ground_bonus=high_ground,
-            base_bonus=base_bonus,
+            base_bonus=base_bonus, melee_penalty=fim_penalty,
+        )
+
+    def _resolve_hit_damage(
+        self,
+        attacker: CombatantState,
+        target: CombatantState,
+        weapon: AttackSpec,
+        *,
+        roll: int,
+        ac: int,
+        base_bonus: int,
+        penalty: int,
+        flank: int,
+        high_ground: int,
+        attack_mod: int,
+        pa_amt: int,
+        fim_penalty: int,
+        dist_ft: int,
+        denies_dex: bool,
+    ) -> tuple[bool, bool, int]:
+        """Resolve a successful attack roll: crit confirm, concealment miss
+        chance, sneak attack dice, then damage (PF1e order).
+
+        Returns ``(crit, concealment_miss, damage)``. Sneak precision dice are
+        added after the crit multiplier and before DR / energy resistance.
+        """
+        crit = False
+        if roll != _NATURAL_ONE and roll >= weapon.crit_range:
+            confirm = self._rng.d20()
+            confirm_total = (
+                confirm + base_bonus + penalty + flank + high_ground
+                + attack_mod - pa_amt + fim_penalty
+            )
+            crit = confirm != _NATURAL_ONE and confirm_total >= ac
+        concealment = self._concealment_chance(target)
+        if concealment > 0:
+            pct = self._rng.d100()
+            missed = pct <= concealment
+            self._log(
+                f"round {self._current_round} {attacker.combatant.id}: "
+                f"concealment vs {target.combatant.id}: "
+                f"d100({pct}) {'<=' if missed else '>'} {concealment}% "
+                f"— attack {'misses' if missed else 'lands'}"
+            )
+            if missed:
+                return False, True, 0
+        sneak_total = 0
+        sneak_dice = self._sneak_attack_dice(
+            attacker, target, weapon, dist_ft=dist_ft,
+            denies_dex=denies_dex, concealment=concealment,
+        )
+        if sneak_dice > 0:
+            sneak_total = sum(self._rng.roll_die(6) for _ in range(sneak_dice))
+            self._log(
+                f"round {self._current_round} {attacker.combatant.id}: "
+                f"sneak attack vs {target.combatant.id}: "
+                f"{sneak_dice}d6 = {sneak_total} precision damage"
+            )
+        dmg_mods = self._stat_modifiers(
+            attacker, "damage", weapon_name=weapon.name, weapon=weapon, dist_ft=dist_ft
+        )
+        damage = (
+            sum(c.formula.roll(self._rng) for c in weapon.damage) + weapon.damage_bonus
+        )
+        damage += resolve_modifiers(dmg_mods)
+        damage += pa_amt * 2 if weapon.kind == "melee" else 0
+        if crit:
+            damage *= weapon.crit_mult
+        damage += sneak_total
+        damage = self._apply_dr(damage, weapon, target)
+        weapon_types = frozenset(t for comp in weapon.damage for t in comp.types)
+        damage = self._apply_energy_resistance(damage, weapon_types, target)
+        return crit, False, damage
+
+    def _concealment_chance(self, target: CombatantState) -> int:
+        """Highest miss chance (%) among the target's active concealment conditions."""
+        chances = [ac.condition.miss_chance for ac in target.active_conditions]
+        chances += [cond.miss_chance for cond in target.conditions]
+        return max((c for c in chances if c > 0), default=0)
+
+    def _sneak_attack_dice(
+        self,
+        attacker: CombatantState,
+        target: CombatantState,
+        weapon: AttackSpec,
+        *,
+        dist_ft: int,
+        denies_dex: bool,
+        concealment: int,
+    ) -> int:
+        """Sneak attack d6 count for this swing (0 when the sneak does not apply).
+
+        PF1e: precision damage when the target is flanked (melee only) or
+        denied its Dex bonus to AC (melee, or ranged within 30 ft); dice =
+        (level + 1) // 2; concealment denies the sneak attack entirely.
+        """
+        if concealment > 0 or not self._has_feat(attacker, _SNEAK_ATTACK_FEATURE):
+            return 0
+        dice = (attacker.combatant.level + 1) // 2
+        is_melee = weapon.kind == "melee"
+        if is_melee and self._flanking_bonus(attacker, target) > 0:
+            return dice
+        if denies_dex and (
+            is_melee
+            or (self._is_ranged_attack(weapon) and dist_ft <= _POINT_BLANK_RANGE_FT)
+        ):
+            return dice
+        return 0
+
+    def _firing_into_melee_penalty(
+        self, attacker: CombatantState, target: CombatantState
+    ) -> int:
+        """PF1e firing into melee: -4 on a ranged attack whose target is
+        engaged in melee, reduced to -2 when the target or every threatening
+        opponent stands 10+ ft from the attacker. Precise Shot removes it.
+
+        The target is engaged when an active enemy of the target (not the
+        attacker itself) threatens the target's occupied cells with a melee
+        weapon.
+        """
+        if self._has_feat(attacker, _PRECISE_SHOT_FEATURE):
+            return 0
+        threats = [
+            s
+            for s in self._states
+            if s is not attacker
+            and s.active
+            and s.side != target.side
+            and self.threatened_squares(s) & target.occupied_cells()
+        ]
+        if not threats:
+            return 0
+        if self.creature_distance(attacker, target) * _SQUARE_FT >= _FIRING_MELEE_SAFE_FT:
+            return _FIRING_MELEE_REDUCED_PENALTY
+        for threat in threats:
+            dist = self.creature_distance(attacker, threat) * _SQUARE_FT
+            if dist >= _FIRING_MELEE_SAFE_FT:
+                return _FIRING_MELEE_REDUCED_PENALTY
+        return _FIRING_MELEE_PENALTY
+
+    def _engaged_in_melee(self, state: CombatantState) -> bool:
+        """True when an active enemy with a melee weapon threatens this
+        combatant's occupied cells (same threat machinery as AoO/flanking)."""
+        occupied = state.occupied_cells()
+        return any(
+            self.threatened_squares(s) & occupied
+            for s in self._states
+            if s is not state and s.active and s.side != state.side
         )
 
     def _consume_up_close_and_deadly(
@@ -3355,10 +3511,11 @@ class CombatEngine:
         high_ground_str = (
             f"+{result.high_ground_bonus}(high)" if result.high_ground_bonus else ""
         )
+        melee_str = f"{result.melee_penalty}(melee)" if result.melee_penalty else ""
         bonus_str = (
-            f"{result.base_bonus}{result.penalty:+d}{flank_str}{high_ground_str}"
+            f"{result.base_bonus}{result.penalty:+d}{flank_str}{high_ground_str}{melee_str}"
             if result.penalty
-            else f"{result.base_bonus}{flank_str}{high_ground_str}"
+            else f"{result.base_bonus}{flank_str}{high_ground_str}{melee_str}"
         )
         line = (
             f"round {self._current_round} {attacker.combatant.id}: {label} "