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

import { describe, expect, it } from "vitest";
import { setInitiative } from "../set-initiative.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, initiative?: number): Combatant {
	return initiative === undefined
		? { id: combatantId(name), name }
		: { id: combatantId(name), name, initiative };
}

const A = makeCombatant("A");
const B = makeCombatant("B");
const C = makeCombatant("C");
function enc(
	combatants: Combatant[],
	activeIndex = 0,
	roundNumber = 1,
): Encounter {
	return { combatants, activeIndex, roundNumber };
}

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

function names(encounter: Encounter): string[] {
	return encounter.combatants.map((c) => c.name);
}

// --- US1: Set Initiative ---

describe("setInitiative", () => {
	describe("US1: set initiative value", () => {
		it("AS-1: set initiative on combatant with no initiative", () => {
			const e = enc([A, B], 0);
			const { encounter, events } = successResult(e, "A", 15);

			expect(encounter.combatants[0].initiative).toBe(15);
			expect(events).toEqual([
				{
					type: "InitiativeSet",
					combatantId: combatantId("A"),
					previousValue: undefined,
					newValue: 15,
				},
			]);
		});

		it("AS-2: change existing initiative value", () => {
			const e = enc([makeCombatant("A", 15), B], 0);
			const { encounter, events } = successResult(e, "A", 8);

			const a = encounter.combatants.find((c) => c.id === combatantId("A"));
			expect(a?.initiative).toBe(8);
			expect(events[0]).toMatchObject({
				previousValue: 15,
				newValue: 8,
			});
		});

		it("AS-3: reject non-integer initiative value", () => {
			const e = enc([A, B], 0);
			const result = setInitiative(e, combatantId("A"), 3.5);

			expectDomainError(result, "invalid-initiative");
		});

		it("AS-3b: reject NaN", () => {
			const e = enc([A, B], 0);
			const result = setInitiative(e, combatantId("A"), Number.NaN);
			expect(isDomainError(result)).toBe(true);
		});

		it("AS-3c: reject Infinity", () => {
			const e = enc([A, B], 0);
			const result = setInitiative(
				e,
				combatantId("A"),
				Number.POSITIVE_INFINITY,
			);
			expect(isDomainError(result)).toBe(true);
		});

		it("AS-4: clear initiative moves combatant to end", () => {
			const e = enc([makeCombatant("A", 15), makeCombatant("B", 10)], 0);
			const { encounter } = successResult(e, "A", undefined);

			const a = encounter.combatants.find((c) => c.id === combatantId("A"));
			expect(a?.initiative).toBeUndefined();
			// A should be after B now
			expect(names(encounter)).toEqual(["B", "A"]);
		});

		it("returns error for nonexistent combatant", () => {
			const e = enc([A, B], 0);
			const result = setInitiative(e, combatantId("nonexistent"), 10);

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

	// --- US2: Automatic Ordering ---

	describe("US2: automatic ordering by initiative", () => {
		it("AS-1: orders combatants descending by initiative", () => {
			// Start with A(20), B(5), C(15) → should be A(20), C(15), B(5)
			const e = enc([
				makeCombatant("A", 20),
				makeCombatant("B", 5),
				makeCombatant("C", 15),
			]);
			// Set C's initiative to trigger reorder (no-op change to force sort)
			const { encounter } = successResult(e, "C", 15);
			expect(names(encounter)).toEqual(["A", "C", "B"]);
		});

		it("AS-2: changing initiative reorders correctly", () => {
			const e = enc([
				makeCombatant("A", 20),
				makeCombatant("C", 15),
				makeCombatant("B", 5),
			]);
			const { encounter } = successResult(e, "B", 25);
			expect(names(encounter)).toEqual(["B", "A", "C"]);
		});

		it("AS-3: stable sort for equal initiative values", () => {
			const e = enc([makeCombatant("A", 10), makeCombatant("B", 10)]);
			// Set A's initiative to same value to confirm stable sort
			const { encounter } = successResult(e, "A", 10);
			expect(names(encounter)).toEqual(["A", "B"]);
		});
	});

	// --- US3: Combatants Without Initiative ---

	describe("US3: combatants without initiative", () => {
		it("AS-1: unset combatants appear after those with initiative", () => {
			const e = enc([
				makeCombatant("A", 15),
				B, // no initiative
				makeCombatant("C", 10),
			]);
			const { encounter } = successResult(e, "A", 15);
			expect(names(encounter)).toEqual(["A", "C", "B"]);
		});

		it("AS-2: multiple unset combatants preserve relative order", () => {
			const e = enc([A, B]); // both no initiative
			const { encounter } = successResult(e, "A", undefined);
			expect(names(encounter)).toEqual(["A", "B"]);
		});

		it("AS-3: setting initiative moves combatant to correct position", () => {
			const e = enc([
				makeCombatant("A", 20),
				B, // no initiative
				makeCombatant("C", 10),
			]);
			const { encounter } = successResult(e, "B", 12);
			expect(names(encounter)).toEqual(["A", "B", "C"]);
		});
	});

	// --- US4: Active Turn Preservation ---

	describe("US4: active turn preservation during reorder", () => {
		it("AS-1: reorder preserves active turn on different combatant", () => {
			// B is active (index 1), change A's initiative
			const e = enc(
				[makeCombatant("A", 10), makeCombatant("B", 15), makeCombatant("C", 5)],
				1,
			);
			// Change A's initiative to 20, causing reorder
			const { encounter } = successResult(e, "A", 20);
			// New order: A(20), B(15), C(5)
			expect(names(encounter)).toEqual(["A", "B", "C"]);
			// B should still be active
			expect(encounter.combatants[encounter.activeIndex].id).toBe(
				combatantId("B"),
			);
		});

		it("AS-2: active combatant's own initiative change preserves turn", () => {
			const e = enc(
				[makeCombatant("A", 20), makeCombatant("B", 15), makeCombatant("C", 5)],
				0, // A is active
			);
			// Change A's initiative to 1, causing it to move to the end
			const { encounter } = successResult(e, "A", 1);
			// New order: B(15), C(5), A(1)
			expect(names(encounter)).toEqual(["B", "C", "A"]);
			// A should still be active
			expect(encounter.combatants[encounter.activeIndex].id).toBe(
				combatantId("A"),
			);
		});
	});

	// --- Invariants ---

	describe("invariants", () => {
		it("determinism — same input produces same output", () => {
			const e = enc([A, B, C], 1, 3);
			const result1 = setInitiative(e, combatantId("A"), 10);
			const result2 = setInitiative(e, combatantId("A"), 10);
			expect(result1).toEqual(result2);
		});

		it("immutability — input encounter is not mutated", () => {
			const e = enc([A, B], 0, 2);
			const original = JSON.parse(JSON.stringify(e));
			setInitiative(e, combatantId("A"), 10);
			expect(e).toEqual(original);
		});

		it("event shape includes all required fields", () => {
			const e = enc([makeCombatant("A", 5), B], 0);
			const { events } = successResult(e, "A", 10);

			expect(events).toHaveLength(1);
			expect(events[0]).toEqual({
				type: "InitiativeSet",
				combatantId: combatantId("A"),
				previousValue: 5,
				newValue: 10,
			});
		});

		it("roundNumber is never changed", () => {
			const e = enc([A, B], 0, 7);
			const { encounter } = successResult(e, "A", 10);
			expect(encounter.roundNumber).toBe(7);
		});

		it("every success emits exactly one InitiativeSet event", () => {
			const scenarios: [Encounter, string, number | undefined][] = [
				[enc([A]), "A", 10],
				[enc([A, B], 1), "A", 5],
				[enc([makeCombatant("A", 10)]), "A", undefined],
			];

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

	// --- Edge Cases ---

	describe("edge cases", () => {
		it("zero is a valid initiative value", () => {
			const e = enc([A, B], 0);
			const { encounter } = successResult(e, "A", 0);
			const a = encounter.combatants.find((c) => c.id === combatantId("A"));
			expect(a?.initiative).toBe(0);
		});

		it("negative initiative is valid", () => {
			const e = enc([A, B], 0);
			const { encounter } = successResult(e, "A", -5);
			const a = encounter.combatants.find((c) => c.id === combatantId("A"));
			expect(a?.initiative).toBe(-5);
		});

		it("negative sorts below positive", () => {
			const e = enc([makeCombatant("A", -3), makeCombatant("B", 10)]);
			const { encounter } = successResult(e, "A", -3);
			expect(names(encounter)).toEqual(["B", "A"]);
		});

		it("all combatants with same initiative preserve order", () => {
			const e = enc([
				makeCombatant("A", 10),
				makeCombatant("B", 10),
				makeCombatant("C", 10),
			]);
			const { encounter } = successResult(e, "B", 10);
			expect(names(encounter)).toEqual(["A", "B", "C"]);
		});

		it("clearing initiative on last combatant with initiative", () => {
			const e = enc([makeCombatant("A", 10), B], 0);
			const { encounter } = successResult(e, "A", undefined);
			// Both unset now, preserve relative order
			expect(names(encounter)).toEqual(["A", "B"]);
		});

		it("undefined value skips integer validation", () => {
			const e = enc([A], 0);
			const result = setInitiative(e, combatantId("A"), undefined);
			expect(isDomainError(result)).toBe(false);
		});
	});
});