feat(combat): skills system

src/pf1e_simulator/combat.py

@@ -81,6 +81,7 @@ from typing import TYPE_CHECKING
 
 from pf1e_simulator.conditions import CONDITIONS_BY_NAME
 from pf1e_simulator.effects import ActiveBuff, ActiveCondition, StatModifier, resolve_modifiers
+from pf1e_simulator.models import PREDEFINED_SKILLS
 from pf1e_simulator.spells import (
     BuffEffect,
     ConditionEffect,
@@ -561,6 +562,39 @@ class CombatEngine:
         success = roll != _NATURAL_ONE and (roll == _NATURAL_TWENTY or total >= dc)
         return SaveResult(success=success, roll=roll, total=total, dc=dc)
 
+    def resolve_skill(
+        self, state: CombatantState, skill: str, dc: int
+    ) -> SaveResult:
+        """Roll a skill check against ``dc``.
+
+        """
+        skill_spec = PREDEFINED_SKILLS.get(skill)
+        if skill_spec is None:
+            msg = f"Unknown skill: {skill}"
+            raise ValueError(msg)
+
+        roll = self._rng.d20()
+        skill_rank = state.combatant.skills.get(skill, None)
+        rank = skill_rank.rank if skill_rank else 0
+        # Class skill bonus
+        class_bonus = 3 if skill_rank and skill_rank.class_skill else 0
+        # Armor check penalty
+        armor_penalty = skill_rank.armor_penalty if skill_rank else 0
+        if armor_penalty and skill_spec.armor_check_penalty:
+            armor_penalty = -abs(armor_penalty)
+        else:
+            armor_penalty = 0
+        # Ability modifier
+        ability_name = skill_spec.ability
+        ability_score = getattr(state.combatant.abilities, f"{ability_name}_score")
+        ability_mod = (ability_score - 10) // 2
+        # Effect/condition modifiers
+        mod_bonus = resolve_modifiers(self._stat_modifiers(state, skill))
+        total = roll + rank + class_bonus + ability_mod + armor_penalty + mod_bonus
+        # Natural 1/20 are not auto-fail/success for skills
+        success = total >= dc
+        return SaveResult(success=success, roll=roll, total=total, dc=dc)
+
     def _roll_initiative(self) -> list[CombatantState]:
         rolls: dict[str, tuple[int, int]] = {}
         for state in self._states: