T007–T011: implement AdvanceTurn domain logic (pure function, events, invariants, 8 acceptance tests)

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

@@ -0,0 +1,233 @@
+import { describe, expect, it } from "vitest";
+import { advanceTurn, isDomainError } from "../advance-turn.js";
+import type { DomainEvent } from "../events.js";
+import {
+	type Combatant,
+	combatantId,
+	createEncounter,
+	type Encounter,
+} 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 = advanceTurn(enc);
+	if (isDomainError(result)) {
+		throw new Error(`Expected success, got error: ${result.message}`);
+	}
+	return result;
+}
+
+// --- Acceptance Scenarios ---
+
+describe("advanceTurn", () => {
+	describe("acceptance scenarios", () => {
+		it("scenario 1: advances from first to second combatant", () => {
+			const enc = encounter([A, B, C], 0, 1);
+			const { encounter: next, events } = successResult(enc);
+
+			expect(next.activeIndex).toBe(1);
+			expect(next.roundNumber).toBe(1);
+			expect(events).toEqual([
+				{
+					type: "TurnAdvanced",
+					previousCombatantId: combatantId("A"),
+					newCombatantId: combatantId("B"),
+					roundNumber: 1,
+				},
+			]);
+		});
+
+		it("scenario 2: advances from second to third combatant", () => {
+			const enc = encounter([A, B, C], 1, 1);
+			const { encounter: next, events } = successResult(enc);
+
+			expect(next.activeIndex).toBe(2);
+			expect(next.roundNumber).toBe(1);
+			expect(events).toEqual([
+				{
+					type: "TurnAdvanced",
+					previousCombatantId: combatantId("B"),
+					newCombatantId: combatantId("C"),
+					roundNumber: 1,
+				},
+			]);
+		});
+
+		it("scenario 3: wraps from last combatant to first, increments round", () => {
+			const enc = encounter([A, B, C], 2, 1);
+			const { encounter: next, events } = successResult(enc);
+
+			expect(next.activeIndex).toBe(0);
+			expect(next.roundNumber).toBe(2);
+			expect(events).toEqual([
+				{
+					type: "TurnAdvanced",
+					previousCombatantId: combatantId("C"),
+					newCombatantId: combatantId("A"),
+					roundNumber: 2,
+				},
+				{
+					type: "RoundAdvanced",
+					newRoundNumber: 2,
+				},
+			]);
+		});
+
+		it("scenario 4: wraps at round 5 to round 6 (not hardcoded)", () => {
+			const enc = encounter([A, B, C], 2, 5);
+			const { encounter: next, events } = successResult(enc);
+
+			expect(next.activeIndex).toBe(0);
+			expect(next.roundNumber).toBe(6);
+			expect(events[0]).toMatchObject({
+				type: "TurnAdvanced",
+				roundNumber: 6,
+			});
+			expect(events[1]).toEqual({
+				type: "RoundAdvanced",
+				newRoundNumber: 6,
+			});
+		});
+
+		it("scenario 5: single combatant always wraps", () => {
+			const enc = encounter([A], 0, 1);
+			const { encounter: next, events } = successResult(enc);
+
+			expect(next.activeIndex).toBe(0);
+			expect(next.roundNumber).toBe(2);
+			expect(events).toEqual([
+				{
+					type: "TurnAdvanced",
+					previousCombatantId: combatantId("A"),
+					newCombatantId: combatantId("A"),
+					roundNumber: 2,
+				},
+				{
+					type: "RoundAdvanced",
+					newRoundNumber: 2,
+				},
+			]);
+		});
+
+		it("scenario 6: two advances on a 2-combatant encounter completes a round", () => {
+			const enc = encounter([A, B], 0, 1);
+
+			const first = successResult(enc);
+			expect(first.encounter.activeIndex).toBe(1);
+			expect(first.encounter.roundNumber).toBe(1);
+
+			const second = successResult(first.encounter);
+			expect(second.encounter.activeIndex).toBe(0);
+			expect(second.encounter.roundNumber).toBe(2);
+		});
+
+		it("scenario 7: empty combatant list returns error", () => {
+			const enc: Encounter = {
+				combatants: [],
+				activeIndex: 0,
+				roundNumber: 1,
+			};
+			const result = advanceTurn(enc);
+
+			expect(isDomainError(result)).toBe(true);
+			if (isDomainError(result)) {
+				expect(result.code).toBe("invalid-encounter");
+			}
+		});
+
+		it("scenario 8: three advances on [A,B,C] completes a full round cycle", () => {
+			let enc = encounter([A, B, C], 0, 1);
+
+			enc = successResult(enc).encounter;
+			enc = successResult(enc).encounter;
+			enc = successResult(enc).encounter;
+
+			expect(enc.activeIndex).toBe(0);
+			expect(enc.roundNumber).toBe(2);
+		});
+	});
+
+	describe("invariants", () => {
+		it("INV-1: createEncounter rejects empty combatant list", () => {
+			const result = createEncounter([]);
+			expect(isDomainError(result)).toBe(true);
+		});
+
+		it("INV-2: activeIndex always in bounds across all scenarios", () => {
+			const combatants = [A, B, C];
+			let enc = encounter(combatants, 0, 1);
+
+			for (let i = 0; i < 10; i++) {
+				const result = successResult(enc);
+				expect(result.encounter.activeIndex).toBeGreaterThanOrEqual(0);
+				expect(result.encounter.activeIndex).toBeLessThan(combatants.length);
+				enc = result.encounter;
+			}
+		});
+
+		it("INV-3: roundNumber never decreases", () => {
+			let enc = encounter([A, B, C], 0, 1);
+			let prevRound = enc.roundNumber;
+
+			for (let i = 0; i < 10; i++) {
+				const result = successResult(enc);
+				expect(result.encounter.roundNumber).toBeGreaterThanOrEqual(prevRound);
+				prevRound = result.encounter.roundNumber;
+				enc = result.encounter;
+			}
+		});
+
+		it("INV-4: determinism — same input produces same output", () => {
+			const enc = encounter([A, B, C], 1, 3);
+			const result1 = advanceTurn(enc);
+			const result2 = advanceTurn(enc);
+			expect(result1).toEqual(result2);
+		});
+
+		it("INV-5: every success emits at least TurnAdvanced", () => {
+			const scenarios: Encounter[] = [
+				encounter([A, B, C], 0, 1),
+				encounter([A, B, C], 2, 1),
+				encounter([A], 0, 1),
+			];
+
+			for (const enc of scenarios) {
+				const result = successResult(enc);
+				const hasTurnAdvanced = result.events.some(
+					(e: DomainEvent) => e.type === "TurnAdvanced",
+				);
+				expect(hasTurnAdvanced).toBe(true);
+			}
+		});
+
+		it("event ordering: on wrap, events are [TurnAdvanced, RoundAdvanced]", () => {
+			const enc = encounter([A, B, C], 2, 1);
+			const { events } = successResult(enc);
+
+			expect(events).toHaveLength(2);
+			expect(events[0].type).toBe("TurnAdvanced");
+			expect(events[1].type).toBe("RoundAdvanced");
+		});
+	});
+});