Implement the 016-combatant-ac feature that adds an optional Armor Class field to combatants with shield icon display and inline editing in the encounter tracker

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/domain/src/__tests__/set-ac.test.ts

@@ -0,0 +1,143 @@
+import { describe, expect, it } from "vitest";
+import { setAc } from "../set-ac.js";
+import type { Combatant, Encounter } from "../types.js";
+import { combatantId, isDomainError } from "../types.js";
+
+function makeCombatant(name: string, ac?: number): Combatant {
+	return ac === undefined
+		? { id: combatantId(name), name }
+		: { id: combatantId(name), name, ac };
+}
+
+function enc(
+	combatants: Combatant[],
+	activeIndex = 0,
+	roundNumber = 1,
+): Encounter {
+	return { combatants, activeIndex, roundNumber };
+}
+
+function successResult(
+	encounter: Encounter,
+	id: string,
+	value: number | undefined,
+) {
+	const result = setAc(encounter, combatantId(id), value);
+	if (isDomainError(result)) {
+		throw new Error(`Expected success, got error: ${result.message}`);
+	}
+	return result;
+}
+
+describe("setAc", () => {
+	it("sets AC to a valid value", () => {
+		const e = enc([makeCombatant("A"), makeCombatant("B")]);
+		const { encounter, events } = successResult(e, "A", 15);
+
+		expect(encounter.combatants[0].ac).toBe(15);
+		expect(events).toEqual([
+			{
+				type: "AcSet",
+				combatantId: combatantId("A"),
+				previousAc: undefined,
+				newAc: 15,
+			},
+		]);
+	});
+
+	it("sets AC to 0", () => {
+		const e = enc([makeCombatant("A")]);
+		const { encounter } = successResult(e, "A", 0);
+
+		expect(encounter.combatants[0].ac).toBe(0);
+	});
+
+	it("clears AC with undefined", () => {
+		const e = enc([makeCombatant("A", 15)]);
+		const { encounter, events } = successResult(e, "A", undefined);
+
+		expect(encounter.combatants[0].ac).toBeUndefined();
+		expect(events[0]).toMatchObject({
+			previousAc: 15,
+			newAc: undefined,
+		});
+	});
+
+	it("returns error for nonexistent combatant", () => {
+		const e = enc([makeCombatant("A")]);
+		const result = setAc(e, combatantId("nonexistent"), 10);
+
+		expect(isDomainError(result)).toBe(true);
+		if (isDomainError(result)) {
+			expect(result.code).toBe("combatant-not-found");
+		}
+	});
+
+	it("returns error for negative AC", () => {
+		const e = enc([makeCombatant("A")]);
+		const result = setAc(e, combatantId("A"), -1);
+
+		expect(isDomainError(result)).toBe(true);
+		if (isDomainError(result)) {
+			expect(result.code).toBe("invalid-ac");
+		}
+	});
+
+	it("returns error for non-integer AC", () => {
+		const e = enc([makeCombatant("A")]);
+		const result = setAc(e, combatantId("A"), 3.5);
+
+		expect(isDomainError(result)).toBe(true);
+		if (isDomainError(result)) {
+			expect(result.code).toBe("invalid-ac");
+		}
+	});
+
+	it("returns error for NaN", () => {
+		const e = enc([makeCombatant("A")]);
+		const result = setAc(e, combatantId("A"), Number.NaN);
+		expect(isDomainError(result)).toBe(true);
+	});
+
+	it("preserves other fields when setting AC", () => {
+		const combatant: Combatant = {
+			id: combatantId("A"),
+			name: "Aria",
+			initiative: 15,
+			maxHp: 20,
+			currentHp: 18,
+		};
+		const e = enc([combatant]);
+		const { encounter } = successResult(e, "A", 16);
+
+		const updated = encounter.combatants[0];
+		expect(updated.ac).toBe(16);
+		expect(updated.name).toBe("Aria");
+		expect(updated.initiative).toBe(15);
+		expect(updated.maxHp).toBe(20);
+		expect(updated.currentHp).toBe(18);
+	});
+
+	it("does not reorder combatants", () => {
+		const e = enc([makeCombatant("A"), makeCombatant("B")]);
+		const { encounter } = successResult(e, "B", 18);
+
+		expect(encounter.combatants[0].id).toBe(combatantId("A"));
+		expect(encounter.combatants[1].id).toBe(combatantId("B"));
+	});
+
+	it("preserves activeIndex and roundNumber", () => {
+		const e = enc([makeCombatant("A"), makeCombatant("B")], 1, 5);
+		const { encounter } = successResult(e, "A", 14);
+
+		expect(encounter.activeIndex).toBe(1);
+		expect(encounter.roundNumber).toBe(5);
+	});
+
+	it("does not mutate input encounter", () => {
+		const e = enc([makeCombatant("A")]);
+		const original = JSON.parse(JSON.stringify(e));
+		setAc(e, combatantId("A"), 10);
+		expect(e).toEqual(original);
+	});
+});

packages/domain/src/events.ts

@@ -68,6 +68,13 @@ export interface RoundRetreated {
 	readonly newRoundNumber: number;
 }
 
+export interface AcSet {
+	readonly type: "AcSet";
+	readonly combatantId: CombatantId;
+	readonly previousAc: number | undefined;
+	readonly newAc: number | undefined;
+}
+
 export type DomainEvent =
 	| TurnAdvanced
 	| RoundAdvanced
@@ -78,4 +85,5 @@ export type DomainEvent =
 	| MaxHpSet
 	| CurrentHpAdjusted
 	| TurnRetreated
-	| RoundRetreated;
+	| RoundRetreated
+	| AcSet;

packages/domain/src/index.ts

@@ -6,6 +6,7 @@ export {
 	editCombatant,
 } from "./edit-combatant.js";
 export type {
+	AcSet,
 	CombatantAdded,
 	CombatantRemoved,
 	CombatantUpdated,
@@ -24,6 +25,7 @@ export {
 	removeCombatant,
 } from "./remove-combatant.js";
 export { retreatTurn } from "./retreat-turn.js";
+export { type SetAcSuccess, setAc } from "./set-ac.js";
 export { type SetHpSuccess, setHp } from "./set-hp.js";
 export {
 	type SetInitiativeSuccess,

packages/domain/src/set-ac.ts

@@ -0,0 +1,56 @@
+import type { DomainEvent } from "./events.js";
+import type { CombatantId, DomainError, Encounter } from "./types.js";
+
+export interface SetAcSuccess {
+	readonly encounter: Encounter;
+	readonly events: DomainEvent[];
+}
+
+export function setAc(
+	encounter: Encounter,
+	combatantId: CombatantId,
+	value: number | undefined,
+): SetAcSuccess | DomainError {
+	const targetIdx = encounter.combatants.findIndex((c) => c.id === combatantId);
+
+	if (targetIdx === -1) {
+		return {
+			kind: "domain-error",
+			code: "combatant-not-found",
+			message: `No combatant found with ID "${combatantId}"`,
+		};
+	}
+
+	if (value !== undefined) {
+		if (!Number.isInteger(value) || value < 0) {
+			return {
+				kind: "domain-error",
+				code: "invalid-ac",
+				message: `AC must be a non-negative integer, got ${value}`,
+			};
+		}
+	}
+
+	const target = encounter.combatants[targetIdx];
+	const previousAc = target.ac;
+
+	const updatedCombatants = encounter.combatants.map((c) =>
+		c.id === combatantId ? { ...c, ac: value } : c,
+	);
+
+	return {
+		encounter: {
+			combatants: updatedCombatants,
+			activeIndex: encounter.activeIndex,
+			roundNumber: encounter.roundNumber,
+		},
+		events: [
+			{
+				type: "AcSet",
+				combatantId,
+				previousAc,
+				newAc: value,
+			},
+		],
+	};
+}

packages/domain/src/types.ts

@@ -11,6 +11,7 @@ export interface Combatant {
 	readonly initiative?: number;
 	readonly maxHp?: number;
 	readonly currentHp?: number;
+	readonly ac?: number;
 }
 
 export interface Encounter {