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

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";
import { expectDomainError } from "./test-helpers.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);

			expectDomainError(result, "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 accepts empty combatant list", () => {
			const result = createEncounter([]);
			expect(isDomainError(result)).toBe(false);
		});

		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");
		});
	});
});