initiative/packages/domain/src/__tests__/undo-redo.test.ts

import { describe, expect, it } from "vitest";
import type { Encounter } from "../types.js";
import { isDomainError } from "../types.js";
import {
	clearHistory,
	EMPTY_UNDO_REDO_STATE,
	pushUndo,
	redo,
	undo,
} from "../undo-redo.js";

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

describe("pushUndo", () => {
	it("adds a snapshot to the undo stack", () => {
		const result = pushUndo(EMPTY_UNDO_REDO_STATE, enc(1));
		expect(result.undoStack).toHaveLength(1);
		expect(result.undoStack[0]).toEqual(enc(1));
	});

	it("clears the redo stack", () => {
		const state = {
			undoStack: [enc(1)],
			redoStack: [enc(2)],
		};
		const result = pushUndo(state, enc(3));
		expect(result.redoStack).toHaveLength(0);
	});

	it("caps the undo stack at 50, dropping the oldest", () => {
		const undoStack = Array.from({ length: 50 }, (_, i) => enc(i + 1));
		const state = { undoStack, redoStack: [] };
		const result = pushUndo(state, enc(51));
		expect(result.undoStack).toHaveLength(50);
		expect(result.undoStack[0]).toEqual(enc(2));
		expect(result.undoStack[49]).toEqual(enc(51));
	});
});

describe("undo", () => {
	it("pops from undo stack and pushes current to redo stack", () => {
		const state = { undoStack: [enc(1)], redoStack: [] };
		const result = undo(state, enc(2));
		expect(isDomainError(result)).toBe(false);
		if (isDomainError(result)) return;
		expect(result.encounter).toEqual(enc(1));
		expect(result.state.undoStack).toHaveLength(0);
		expect(result.state.redoStack).toEqual([enc(2)]);
	});

	it("returns domain error when undo stack is empty", () => {
		const result = undo(EMPTY_UNDO_REDO_STATE, enc(1));
		expect(isDomainError(result)).toBe(true);
		if (!isDomainError(result)) return;
		expect(result.code).toBe("nothing-to-undo");
	});

	it("pops the most recent entry (last in stack)", () => {
		const state = { undoStack: [enc(1), enc(2), enc(3)], redoStack: [] };
		const result = undo(state, enc(4));
		expect(isDomainError(result)).toBe(false);
		if (isDomainError(result)) return;
		expect(result.encounter).toEqual(enc(3));
		expect(result.state.undoStack).toEqual([enc(1), enc(2)]);
	});
});

describe("redo", () => {
	it("pops from redo stack and pushes current to undo stack", () => {
		const state = { undoStack: [], redoStack: [enc(1)] };
		const result = redo(state, enc(2));
		expect(isDomainError(result)).toBe(false);
		if (isDomainError(result)) return;
		expect(result.encounter).toEqual(enc(1));
		expect(result.state.redoStack).toHaveLength(0);
		expect(result.state.undoStack).toEqual([enc(2)]);
	});

	it("returns domain error when redo stack is empty", () => {
		const result = redo(EMPTY_UNDO_REDO_STATE, enc(1));
		expect(isDomainError(result)).toBe(true);
		if (!isDomainError(result)) return;
		expect(result.code).toBe("nothing-to-redo");
	});

	it("pops the most recent entry (last in stack)", () => {
		const state = { undoStack: [], redoStack: [enc(1), enc(2), enc(3)] };
		const result = redo(state, enc(4));
		expect(isDomainError(result)).toBe(false);
		if (isDomainError(result)) return;
		expect(result.encounter).toEqual(enc(3));
		expect(result.state.redoStack).toEqual([enc(1), enc(2)]);
	});
});

describe("undo-then-redo roundtrip", () => {
	it("returns the exact same encounter after undo then redo", () => {
		const original = enc(5);
		const current = enc(6);
		const afterPush = pushUndo(EMPTY_UNDO_REDO_STATE, original);

		const undoResult = undo(afterPush, current);
		expect(isDomainError(undoResult)).toBe(false);
		if (isDomainError(undoResult)) return;

		expect(undoResult.encounter).toEqual(original);

		const redoResult = redo(undoResult.state, undoResult.encounter);
		expect(isDomainError(redoResult)).toBe(false);
		if (isDomainError(redoResult)) return;

		expect(redoResult.encounter).toEqual(current);
	});
});

describe("clearHistory", () => {
	it("empties both stacks", () => {
		const result = clearHistory();
		expect(result.undoStack).toHaveLength(0);
		expect(result.redoStack).toHaveLength(0);
	});
});