Implement the 012-turn-navigation feature that adds a RetreatTurn domain operation and relocates turn controls to a navigation bar at the top of the encounter tracker

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

packages/domain/src/__tests__/retreat-turn.test.ts

@@ -0,0 +1,184 @@
+import { describe, expect, it } from "vitest";
+import type { DomainEvent } from "../events.js";
+import { retreatTurn } from "../retreat-turn.js";
+import {
+	type Combatant,
+	combatantId,
+	createEncounter,
+	type Encounter,
+	isDomainError,
+} from "../types.js";
+
+// --- Helpers ---
+
+function makeCombatant(name: string): Combatant {
+	return { id: combatantId(name), name };
+}
+
+const A = makeCombatant("A");
+const B = makeCombatant("B");
+const C = makeCombatant("C");
+
+function encounter(
+	combatants: Combatant[],
+	activeIndex: number,
+	roundNumber: number,
+): Encounter {
+	const result = createEncounter(combatants, activeIndex, roundNumber);
+	if (isDomainError(result)) {
+		throw new Error(`Test setup failed: ${result.message}`);
+	}
+	return result;
+}
+
+function successResult(enc: Encounter) {
+	const result = retreatTurn(enc);
+	if (isDomainError(result)) {
+		throw new Error(`Expected success, got error: ${result.message}`);
+	}
+	return result;
+}
+
+// --- Acceptance Scenarios ---
+
+describe("retreatTurn", () => {
+	describe("acceptance scenarios", () => {
+		it("scenario 1: mid-round retreat — retreats from second to first combatant", () => {
+			const enc = encounter([A, B, C], 1, 1);
+			const { encounter: next, events } = successResult(enc);
+
+			expect(next.activeIndex).toBe(0);
+			expect(next.roundNumber).toBe(1);
+			expect(events).toEqual([
+				{
+					type: "TurnRetreated",
+					previousCombatantId: combatantId("B"),
+					newCombatantId: combatantId("A"),
+					roundNumber: 1,
+				},
+			]);
+		});
+
+		it("scenario 2: round-boundary retreat — wraps from first combatant to last, decrements round", () => {
+			const enc = encounter([A, B, C], 0, 2);
+			const { encounter: next, events } = successResult(enc);
+
+			expect(next.activeIndex).toBe(2);
+			expect(next.roundNumber).toBe(1);
+			expect(events).toEqual([
+				{
+					type: "TurnRetreated",
+					previousCombatantId: combatantId("A"),
+					newCombatantId: combatantId("C"),
+					roundNumber: 1,
+				},
+				{
+					type: "RoundRetreated",
+					newRoundNumber: 1,
+				},
+			]);
+		});
+
+		it("scenario 3: start-of-encounter error — cannot retreat at round 1 index 0", () => {
+			const enc = encounter([A, B, C], 0, 1);
+			const result = retreatTurn(enc);
+
+			expect(isDomainError(result)).toBe(true);
+			if (isDomainError(result)) {
+				expect(result.code).toBe("no-previous-turn");
+			}
+		});
+
+		it("scenario 4: single-combatant retreat — wraps to same combatant, decrements round", () => {
+			const enc = encounter([A], 0, 2);
+			const { encounter: next, events } = successResult(enc);
+
+			expect(next.activeIndex).toBe(0);
+			expect(next.roundNumber).toBe(1);
+			expect(events).toEqual([
+				{
+					type: "TurnRetreated",
+					previousCombatantId: combatantId("A"),
+					newCombatantId: combatantId("A"),
+					roundNumber: 1,
+				},
+				{
+					type: "RoundRetreated",
+					newRoundNumber: 1,
+				},
+			]);
+		});
+
+		it("scenario 5: empty-encounter error", () => {
+			const enc: Encounter = {
+				combatants: [],
+				activeIndex: 0,
+				roundNumber: 1,
+			};
+			const result = retreatTurn(enc);
+
+			expect(isDomainError(result)).toBe(true);
+			if (isDomainError(result)) {
+				expect(result.code).toBe("invalid-encounter");
+			}
+		});
+	});
+
+	describe("invariants", () => {
+		it("determinism — same input produces same output", () => {
+			const enc = encounter([A, B, C], 1, 3);
+			const result1 = retreatTurn(enc);
+			const result2 = retreatTurn(enc);
+			expect(result1).toEqual(result2);
+		});
+
+		it("activeIndex always in bounds after retreat", () => {
+			const combatants = [A, B, C];
+			// Start at round 4 so we can retreat many times
+			let enc = encounter(combatants, 2, 4);
+
+			for (let i = 0; i < 9; i++) {
+				const result = successResult(enc);
+				expect(result.encounter.activeIndex).toBeGreaterThanOrEqual(0);
+				expect(result.encounter.activeIndex).toBeLessThan(combatants.length);
+				enc = result.encounter;
+			}
+		});
+
+		it("roundNumber never goes below 1", () => {
+			let enc = encounter([A, B, C], 2, 2);
+
+			// Retreat through rounds — should stop at round 1 index 0
+			while (!(enc.roundNumber === 1 && enc.activeIndex === 0)) {
+				const result = successResult(enc);
+				expect(result.encounter.roundNumber).toBeGreaterThanOrEqual(1);
+				enc = result.encounter;
+			}
+		});
+
+		it("every success emits at least TurnRetreated", () => {
+			const scenarios: Encounter[] = [
+				encounter([A, B, C], 1, 1),
+				encounter([A, B, C], 0, 2),
+				encounter([A], 0, 2),
+			];
+
+			for (const enc of scenarios) {
+				const result = successResult(enc);
+				const hasTurnRetreated = result.events.some(
+					(e: DomainEvent) => e.type === "TurnRetreated",
+				);
+				expect(hasTurnRetreated).toBe(true);
+			}
+		});
+
+		it("event ordering: on wrap, events are [TurnRetreated, RoundRetreated]", () => {
+			const enc = encounter([A, B, C], 0, 2);
+			const { events } = successResult(enc);
+
+			expect(events).toHaveLength(2);
+			expect(events[0].type).toBe("TurnRetreated");
+			expect(events[1].type).toBe("RoundRetreated");
+		});
+	});
+});