import { describe, expect, it, vi } from "vitest";

import { MAX_CONTEXT_LOSSES, WebglPolicy } from "./webglRenderer.js";

describe("WebglPolicy", () => {
  it("is enabled when the browser supports WebGL2", () => {
    expect(new WebglPolicy(() => true).enabled()).toBe(true);
  });

  it("is disabled when the browser has no WebGL2", () => {
    expect(new WebglPolicy(() => false).enabled()).toBe(false);
  });

  it("probes only once, however often it is asked", () => {
    const probe = vi.fn(() => true);
    const policy = new WebglPolicy(probe);
    policy.enabled();
    policy.enabled();
    policy.enabled();
    expect(probe).toHaveBeenCalledTimes(1);
  });

  it("tolerates a loss below the budget — a backgrounded tab is ordinary", () => {
    const policy = new WebglPolicy(() => true);
    policy.noteContextLoss();
    expect(policy.enabled()).toBe(true);
  });

  it("gives up for good once losses reach the budget", () => {
    const policy = new WebglPolicy(() => true);
    for (let i = 0; i < MAX_CONTEXT_LOSSES; i++) policy.noteContextLoss();
    expect(policy.enabled()).toBe(false);
    expect(policy.contextLosses()).toBe(MAX_CONTEXT_LOSSES);
  });

  it("stays disabled past the budget, and never bothers probing", () => {
    const probe = vi.fn(() => true);
    const policy = new WebglPolicy(probe);
    for (let i = 0; i < MAX_CONTEXT_LOSSES + 3; i++) policy.noteContextLoss();
    expect(policy.enabled()).toBe(false);
    expect(probe).not.toHaveBeenCalled();
  });

  it("treats a throwing probe as unsupported", () => {
    const policy = new WebglPolicy(() => {
      throw new Error("no gl for you");
    });
    expect(() => policy.enabled()).not.toThrow();
    expect(policy.enabled()).toBe(false);
  });

  it("reports no WebGL2 under the test DOM, which has no GPU", () => {
    expect(new WebglPolicy().enabled()).toBe(false);
  });
});