feat(api): add CharacterStatsService as authoritative effective-stat source

apps/api/src/characters/character-stats.service.ts

@@ -0,0 +1,64 @@
+import { Injectable } from '@nestjs/common';
+import { DataSource } from 'typeorm';
+import { CharacterEquipment } from '../equipment/entities/character-equipment.entity';
+import { EquipmentSlot } from '../items/equipment-slot.enum';
+import { Character } from './entities/character.entity';
+
+export interface EffectiveCharacterStats {
+  maxHp: number;
+  currentHp: number;
+  attack: number;
+  weaponDamage: number;
+  armor: number;
+  combatPower: number;
+}
+
+type RepositoryScope = Pick<DataSource, 'getRepository'>;
+
+/**
+ * Single authoritative source of effective character stats (spec §18).
+ * Replaces the Slice 0.3 `CharacterCombatStatsService` shortcut.
+ */
+@Injectable()
+export class CharacterStatsService {
+  constructor(private readonly dataSource: DataSource) {}
+
+  async calculate(
+    character: Character,
+    scope?: RepositoryScope,
+  ): Promise<EffectiveCharacterStats> {
+    const db = scope ?? this.dataSource;
+    const equipped = await db.getRepository(CharacterEquipment).find({
+      where: { characterId: character.id },
+      relations: { characterItem: { itemDefinition: true } },
+    });
+
+    let weaponDamage = 0;
+    let bonusHp = 0;
+    let bonusAttack = 0;
+    let bonusArmor = 0;
+
+    for (const slot of equipped) {
+      const definition = slot.characterItem.itemDefinition;
+      if (slot.slot === EquipmentSlot.WEAPON) {
+        weaponDamage = definition.weaponDamage;
+      }
+      bonusHp += definition.bonusHp;
+      bonusAttack += definition.bonusAttack;
+      bonusArmor += definition.bonusArmor;
+    }
+
+    const maxHp = character.baseHp + bonusHp;
+    const attack = character.baseAttack + bonusAttack;
+    const armor = bonusArmor;
+
+    return {
+      maxHp,
+      currentHp: character.currentHp,
+      attack,
+      weaponDamage,
+      armor,
+      combatPower: maxHp / 10 + attack * 2 + weaponDamage * 2 + armor * 1.5,
+    };
+  }
+}