import { describe, it, expect, beforeEach, vi } from "vitest";
import { World, defineComponent, type Entity } from "../src/index";
import { CommandQueue } from "../src/commands/command-queue";

// ── Components ──────────────────────────────────────
const Health = defineComponent("health", { current: 100, max: 100 });
const DamageCmd = defineComponent("damageCmd", { amount: 0 });
const HealCmd = defineComponent("healCmd", { amount: 0 });

// ── Helpers ─────────────────────────────────────────
async function settled() {
  await new Promise((r) => setTimeout(r, 0));
}

// ── Basic command dispatch ──────────────────────────
describe("CommandQueue", () => {
  let world: World;
  let queue: CommandQueue;

  beforeEach(() => {
    world = new World();
    queue = new CommandQueue(world);
  });

  it("dispatches commands to registered handlers", () => {
    const results: { entity: Entity; amount: number }[] = [];

    queue.handle(DamageCmd, (cmd, entity) => {
      results.push({ entity: entity!, amount: cmd.amount });
    });

    const e = world.spawn();
    world.add(e, DamageCmd, { amount: 25 });

    queue.execute();

    expect(results).toHaveLength(1);
    expect(results[0].amount).toBe(25);
  });

  it("removes the command component after dispatch", () => {
    queue.handle(DamageCmd, () => {});

    const e = world.spawn();
    world.add(e, DamageCmd, { amount: 10 });

    expect(world.has(e, DamageCmd)).toBe(true);

    queue.execute();

    expect(world.has(e, DamageCmd)).toBe(false);
  });

  it("destroys an entity when it becomes empty after command removal", () => {
    queue.handle(DamageCmd, () => {});

    const e = world.spawn();
    world.add(e, DamageCmd, { amount: 10 });

    queue.execute();

    expect(world.isAlive(e)).toBe(false);
  });

  it("does NOT destroy entities that still have other components", () => {
    queue.handle(DamageCmd, () => {});

    const e = world.spawn();
    world.add(e, Health);
    world.add(e, DamageCmd, { amount: 10 });

    queue.execute();

    expect(world.isAlive(e)).toBe(true);
    expect(world.has(e, Health)).toBe(true);
    expect(world.has(e, DamageCmd)).toBe(false);
  });

  it("handles multiple entities with the same command type", () => {
    const hits: Entity[] = [];
    queue.handle(DamageCmd, (_, entity) => {
      hits.push(entity!);
    });

    const a = world.spawn();
    const b = world.spawn();
    const c = world.spawn();
    world.add(a, DamageCmd, { amount: 5 });
    world.add(b, DamageCmd, { amount: 10 });
    world.add(c, DamageCmd, { amount: 15 });

    queue.execute();

    expect(hits).toHaveLength(3);
  });

  it("handles multiple registered command types", () => {
    const damages: number[] = [];
    const heals: number[] = [];

    queue
      .handle(DamageCmd, (cmd) => damages.push(cmd.amount))
      .handle(HealCmd, (cmd) => heals.push(cmd.amount));

    const a = world.spawn();
    const b = world.spawn();
    world.add(a, DamageCmd, { amount: 5 });
    world.add(b, HealCmd, { amount: 20 });

    queue.execute();

    expect(damages).toEqual([5]);
    expect(heals).toEqual([20]);
    expect(world.has(a, DamageCmd)).toBe(false);
    expect(world.has(b, HealCmd)).toBe(false);
  });

  it("is a no-op when no command entities exist", () => {
    queue.handle(DamageCmd, () => {
      throw new Error("should not be called");
    });

    // No entities with DamageCmd

    expect(() => queue.execute()).not.toThrow();
  });

  it("is a no-op when no handlers are registered", () => {
    const e = world.spawn();
    world.add(e, DamageCmd, { amount: 10 });

    expect(() => queue.execute()).not.toThrow();
    expect(world.has(e, DamageCmd)).toBe(true); // not consumed
  });
});

// ── Interruption ────────────────────────────────────
describe("CommandQueue interruption", () => {
  let world: World;
  let queue: CommandQueue;

  beforeEach(() => {
    world = new World();
    queue = new CommandQueue(world);
  });

  it("skips processing when interrupted", () => {
    const handler = vi.fn();
    queue.handle(DamageCmd, handler);

    const e = world.spawn();
    world.add(e, DamageCmd, { amount: 10 });

    // Interrupt with a never-resolving promise
    queue.interrupt(new Promise(() => {}));

    expect(queue.isInterrupted).toBe(true);

    queue.execute();

    expect(handler).not.toHaveBeenCalled();
    expect(world.has(e, DamageCmd)).toBe(true);
  });

  it("resumes processing after interruption promise resolves", async () => {
    const handler = vi.fn();
    queue.handle(DamageCmd, handler);

    let resolve!: () => void;
    const promise = new Promise<void>((r) => {
      resolve = r;
    });

    queue.interrupt(promise);
    expect(queue.isInterrupted).toBe(true);

    queue.execute();
    expect(handler).not.toHaveBeenCalled();

    resolve();
    await settled();

    expect(queue.isInterrupted).toBe(false);

    const e = world.spawn();
    world.add(e, DamageCmd, { amount: 10 });

    queue.execute();
    expect(handler).toHaveBeenCalledTimes(1);
  });

  it("resumes after all interruption promises settle (including rejections)", async () => {
    const handler = vi.fn();
    queue.handle(DamageCmd, handler);

    queue.interrupt(Promise.reject(new Error("fail")));
    await settled();
    expect(queue.isInterrupted).toBe(false);

    const e = world.spawn();
    world.add(e, DamageCmd, { amount: 10 });
    queue.execute();
    expect(handler).toHaveBeenCalledTimes(1);
  });

  it("stays interrupted while at least one of several promises is pending", async () => {
    let resolveA!: () => void;
    const a = new Promise<void>((r) => {
      resolveA = r;
    });
    const b = Promise.resolve();

    queue.interrupt(a);
    queue.interrupt(b);

    await settled(); // b resolves
    expect(queue.isInterrupted).toBe(true); // a still pending

    resolveA();
    await settled();
    expect(queue.isInterrupted).toBe(false);
  });
});

// ── Edge cases ──────────────────────────────────────
describe("CommandQueue edge cases", () => {
  it("handler can safely add components to surviving entity", () => {
    const world = new World();
    const queue = new CommandQueue(world);
    const Flag = defineComponent("flag", { set: false });

    queue.handle(DamageCmd, (_cmd, entity) => {
      world.add(entity!, Flag, { set: true });
    });

    const e = world.spawn();
    world.add(e, Health);
    world.add(e, DamageCmd, { amount: 10 });

    queue.execute();

    expect(world.has(e, Flag)).toBe(true);
    expect(world.isAlive(e)).toBe(true);
  });

  it("handler can destroy a different entity", () => {
    const world = new World();
    const queue = new CommandQueue(world);

    const other = world.spawn();
    queue.handle(DamageCmd, () => {
      world.destroy(other);
    });

    const e = world.spawn();
    world.add(e, DamageCmd, { amount: 10 });

    queue.execute();

    expect(world.isAlive(other)).toBe(false);
  });

  it("chainable .handle() calls", () => {
    const world = new World();
    const queue = new CommandQueue(world);

    const a = vi.fn();
    const b = vi.fn();

    queue
      .handle(DamageCmd, (_cmd, _entity) => a())
      .handle(HealCmd, (_cmd, _entity) => b());

    const e1 = world.spawn();
    world.add(e1, DamageCmd, { amount: 5 });
    const e2 = world.spawn();
    world.add(e2, HealCmd, { amount: 10 });

    queue.execute();

    expect(a).toHaveBeenCalled();
    expect(b).toHaveBeenCalled();
  });
});