initiative/packages/domain/src/__tests__/remove-combatant.test.ts

import { describe, expect, it } from "vitest";
import { removeCombatant } from "../remove-combatant.js";
import type { Combatant, Encounter } from "../types.js";
import { combatantId, isDomainError } 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");
const D = makeCombatant("D");

function enc(
	combatants: Combatant[],
	activeIndex = 0,
	roundNumber = 1,
): Encounter {
	return { combatants, activeIndex, roundNumber };
}

function successResult(encounter: Encounter, id: string) {
	const result = removeCombatant(encounter, combatantId(id));
	if (isDomainError(result)) {
		throw new Error(`Expected success, got error: ${result.message}`);
	}
	return result;
}

// --- Acceptance Scenarios ---

describe("removeCombatant", () => {
	describe("acceptance scenarios", () => {
		it("AS-1: remove combatant after active — activeIndex unchanged", () => {
			// [A*, B, C] remove C → [A*, B], activeIndex stays 0
			const e = enc([A, B, C], 0, 2);
			const { encounter, events } = successResult(e, "C");

			expect(encounter.combatants).toEqual([A, B]);
			expect(encounter.activeIndex).toBe(0);
			expect(encounter.roundNumber).toBe(2);
			expect(events).toEqual([
				{
					type: "CombatantRemoved",
					combatantId: combatantId("C"),
					name: "C",
				},
			]);
		});

		it("AS-2: remove combatant before active — activeIndex decrements", () => {
			// [A, B, C*] remove A → [B, C*], activeIndex 2→1
			const e = enc([A, B, C], 2, 3);
			const { encounter } = successResult(e, "A");

			expect(encounter.combatants).toEqual([B, C]);
			expect(encounter.activeIndex).toBe(1);
			expect(encounter.roundNumber).toBe(3);
		});

		it("AS-3: remove active combatant mid-list — next slides in", () => {
			// [A, B*, C, D] remove B → [A, C*, D], activeIndex stays 1
			const e = enc([A, B, C, D], 1, 1);
			const { encounter } = successResult(e, "B");

			expect(encounter.combatants).toEqual([A, C, D]);
			expect(encounter.activeIndex).toBe(1);
		});

		it("AS-4: remove active combatant at end — wraps to 0", () => {
			// [A, B, C*] remove C → [A, B], activeIndex wraps to 0
			const e = enc([A, B, C], 2, 1);
			const { encounter } = successResult(e, "C");

			expect(encounter.combatants).toEqual([A, B]);
			expect(encounter.activeIndex).toBe(0);
		});

		it("AS-5: remove only combatant — empty list, activeIndex 0", () => {
			const e = enc([A], 0, 5);
			const { encounter } = successResult(e, "A");

			expect(encounter.combatants).toEqual([]);
			expect(encounter.activeIndex).toBe(0);
			expect(encounter.roundNumber).toBe(5);
		});

		it("AS-6: ID not found — returns DomainError", () => {
			const e = enc([A, B], 0, 1);
			const result = removeCombatant(e, combatantId("nonexistent"));

			expectDomainError(result, "combatant-not-found");
		});
	});

	describe("invariants", () => {
		it("event shape includes combatantId and name", () => {
			const e = enc([A, B], 0, 1);
			const { events } = successResult(e, "B");

			expect(events).toHaveLength(1);
			expect(events[0]).toEqual({
				type: "CombatantRemoved",
				combatantId: combatantId("B"),
				name: "B",
			});
		});

		it("roundNumber never changes on removal", () => {
			const e = enc([A, B, C], 1, 7);
			const { encounter } = successResult(e, "A");
			expect(encounter.roundNumber).toBe(7);
		});

		it("determinism — same input produces same output", () => {
			const e = enc([A, B, C], 1, 3);
			const result1 = removeCombatant(e, combatantId("B"));
			const result2 = removeCombatant(e, combatantId("B"));
			expect(result1).toEqual(result2);
		});

		it("every success emits exactly one CombatantRemoved event", () => {
			const scenarios: [Encounter, string][] = [
				[enc([A]), "A"],
				[enc([A, B], 1), "A"],
				[enc([A, B, C], 2, 5), "C"],
			];

			for (const [e, id] of scenarios) {
				const { events } = successResult(e, id);
				expect(events).toHaveLength(1);
				expect(events[0].type).toBe("CombatantRemoved");
			}
		});
	});
});