import { describe, expect, it, vi } from 'vitest';
import {
  createSceneController,
  createSceneLifecycleMachine,
} from '@/scene/create-scene-controller';
import type {
  SceneBuildContext,
  SceneGeneration,
  SceneLifecycleState,
  SceneScheduler,
} from '@/scene/types';
import type { JourneySnapshot } from '@/journey/types';

const state = (kind: SceneLifecycleState['kind']): SceneLifecycleState => {
  switch (kind) {
    case 'idle': return { kind };
    case 'loading': return { kind, generation: 1 };
    case 'running': return { kind, generation: 1 };
    case 'paused': return { kind, generation: null, resumeNeedsLoad: true };
    case 'lost': return { kind, lostAt: 100, restorationPending: false };
    case 'restoring': return { kind, generation: 2, lostAt: 100 };
    case 'static': return { kind, reason: 'test' };
    case 'disposed': return { kind };
  }
};

describe('scene lifecycle machine', () => {
  const legal: Readonly<Record<SceneLifecycleState['kind'], readonly SceneLifecycleState['kind'][]>> = {
    idle: ['loading', 'paused', 'static', 'disposed'],
    loading: ['running', 'paused', 'lost', 'static', 'disposed'],
    running: ['paused', 'lost', 'static', 'disposed'],
    paused: ['running', 'loading', 'static', 'disposed'],
    lost: ['restoring', 'paused', 'static', 'disposed'],
    restoring: ['running', 'paused', 'lost', 'static', 'disposed'],
    static: ['loading', 'disposed'],
    disposed: [],
  };

  for (const from of Object.keys(legal) as SceneLifecycleState['kind'][]) {
    for (const to of Object.keys(legal) as SceneLifecycleState['kind'][]) {
      if (from === to) continue;
      const expected = legal[from].includes(to) || (from === 'paused' && to === 'lost');
      it(`${expected ? 'allows' : 'rejects'} ${from} -> ${to}`, () => {
        const initial = from === 'paused' && to === 'lost'
          ? { kind: 'paused' as const, generation: 1, resumeNeedsLoad: false }
          : state(from);
        const machine = createSceneLifecycleMachine(initial);
        if (expected) {
          expect(() => machine.transition(state(to))).not.toThrow();
          expect(machine.snapshot().kind).toBe(to);
        } else {
          expect(() => machine.transition(state(to))).toThrow(/illegal transition/i);
        }
      });
    }
  }

  it('rejects paused -> lost when no complete retained context exists', () => {
    const machine = createSceneLifecycleMachine({
      kind: 'paused', generation: null, resumeNeedsLoad: true,
    });
    expect(() => machine.transition(state('lost'))).toThrow(/retained context/i);
  });

  it('keeps disposed terminal', () => {
    const machine = createSceneLifecycleMachine({ kind: 'disposed' });
    expect(() => machine.transition({ kind: 'running', generation: 9 })).toThrow(/illegal transition/i);
  });
});

describe('scene controller lifecycle', () => {
  it('attaches one generation and schedules at most one RAF', async () => {
    const harness = createHarness();
    const controller = createSceneController(harness.options);

    await controller.start();
    expect(controller.snapshot()).toMatchObject({
      state: { kind: 'running', generation: 1 },
      canvasCount: 1,
      rafCount: 1,
      currentGeneration: 1,
    });

    controller.resume();
    controller.resume();
    expect(controller.snapshot().rafCount).toBe(1);
    harness.scheduler.flushFrame(16);
    expect(controller.snapshot().rafCount).toBe(1);
    expect(harness.generations[0]?.render).toHaveBeenCalledOnce();
  });

  it('samples the complete scene update and render interval', async () => {
    const harness = createHarness();
    const renderedFrames: Array<{ start: number; end: number }> = [];
    const controller = createSceneController({
      ...harness.options,
      onFrameRendered: (start, end) => renderedFrames.push({ start, end }),
    });
    await controller.start();
    harness.generations[0]?.render.mockImplementation(() => {
      harness.clock.now += 300;
    });

    harness.scheduler.flushFrame(2_000);

    expect(renderedFrames).toEqual([{ start: 2_000, end: 2_300 }]);
  });

  it('enters static five seconds after a live-scene request that never completes its first frame', async () => {
    const harness = createHarness({ deferredBuild: true });
    const controller = createSceneController(harness.options);
    const start = controller.start();

    harness.scheduler.flushTimers(4_999);
    expect(controller.snapshot().state.kind).toBe('loading');

    harness.scheduler.flushTimers(5_000);
    expect(controller.snapshot()).toMatchObject({
      state: { kind: 'static', reason: 'first-frame-timeout' },
      currentGeneration: null,
      rafCount: 0,
    });
    expect(harness.buildContexts[0]?.signal.aborted).toBe(true);

    harness.resolveBuild(0);
    await start;
    expect(harness.generations[0]?.dispose).toHaveBeenCalledOnce();
  });

  it('cancels the first-frame watchdog only after a complete update and render', async () => {
    const harness = createHarness();
    const controller = createSceneController(harness.options);
    await controller.start();

    harness.scheduler.flushFrame(16);
    harness.scheduler.flushTimers(5_001);

    expect(controller.snapshot()).toMatchObject({
      state: { kind: 'running', generation: 1 },
      currentGeneration: 1,
      rafCount: 1,
    });
    expect(harness.generations[0]?.dispose).not.toHaveBeenCalled();
  });

  it('keeps the watchdog armed when a frame explicitly reports incomplete', async () => {
    const harness = createHarness();
    const onFrameRendered = vi.fn();
    const controller = createSceneController({ ...harness.options, onFrameRendered });
    await controller.start();
    harness.generations[0]?.render.mockReturnValue(false);

    harness.scheduler.flushFrame(16);
    harness.scheduler.flushTimers(5_000);

    expect(controller.snapshot()).toMatchObject({
      state: { kind: 'static', reason: 'first-frame-timeout' },
      currentGeneration: null,
      rafCount: 0,
    });
    expect(harness.generations[0]?.dispose).toHaveBeenCalledOnce();
    expect(onFrameRendered).not.toHaveBeenCalled();
  });

  it('replaces a torn-down generation watchdog with one deadline for its restart', async () => {
    const harness = createHarness({ deferredBuild: true });
    const controller = createSceneController(harness.options);
    const first = controller.start();
    harness.clock.now = 1_000;
    controller.pause();
    const second = controller.resume();

    harness.scheduler.flushTimers(5_000);
    expect(controller.snapshot()).toMatchObject({ state: { kind: 'loading', generation: 2 } });

    harness.scheduler.flushTimers(6_000);
    expect(controller.snapshot().state).toEqual({ kind: 'static', reason: 'first-frame-timeout' });
    harness.resolveBuild(0);
    harness.resolveBuild(1);
    await Promise.all([first, second]);
    expect(harness.generations[0]?.dispose).toHaveBeenCalledOnce();
    expect(harness.generations[1]?.dispose).toHaveBeenCalledOnce();
  });

  it('retains the same complete generation and frame across a visitor pause', async () => {
    const harness = createHarness();
    const controller = createSceneController(harness.options);
    await controller.start();
    const running = controller.snapshot();

    controller.pause();

    expect(controller.snapshot()).toMatchObject({
      state: { kind: 'paused', generation: running.currentGeneration, resumeNeedsLoad: false },
      currentGeneration: running.currentGeneration,
      canvasCount: 1,
      rafCount: 0,
    });
    expect(harness.generations).toHaveLength(1);
    expect(harness.generations[0]?.dispose).not.toHaveBeenCalled();

    await controller.resume();

    expect(controller.snapshot()).toMatchObject({
      state: { kind: 'running', generation: running.currentGeneration },
      currentGeneration: running.currentGeneration,
      canvasCount: 1,
      rafCount: 1,
    });
    expect(harness.generations).toHaveLength(1);
  });

  it('copies serializable journey snapshots instead of retaining caller objects', async () => {
    const harness = createHarness();
    const controller = createSceneController(harness.options);
    await controller.start();
    const input = journey({
      routeProgress: 0.25,
      sign: {
        targetId: 'selected-builds',
        phase: 'approach',
        progress: 0.2,
        opacity: 0.5,
        viewportProfile: 'wide',
      },
    });

    controller.update(input);
    input.routeProgress = 0.9;
    if (input.sign) input.sign.progress = 0.8;
    harness.scheduler.flushFrame(16);

    expect(harness.generations[0]?.render).toHaveBeenCalledWith(
      expect.objectContaining({
        routeProgress: 0.25,
        sign: expect.objectContaining({ progress: 0.2, viewportProfile: 'wide' }),
      }),
      16,
    );
  });

  it('invalidates and disposes an aborted loading generation before a late completion can attach', async () => {
    const harness = createHarness({ deferredBuild: true });
    const controller = createSceneController(harness.options);
    const start = controller.start();
    expect(controller.snapshot().state.kind).toBe('loading');

    controller.pause();
    expect(harness.buildContexts[0]?.signal.aborted).toBe(true);
    harness.resolveBuild(0);
    await start;

    expect(harness.generations[0]?.dispose).toHaveBeenCalledOnce();
    expect(controller.snapshot()).toMatchObject({
      state: { kind: 'paused', generation: null, resumeNeedsLoad: true },
      currentGeneration: null,
      rafCount: 0,
    });
  });

  it('disposes stale async results and lets only the current generation attach', async () => {
    const harness = createHarness({ deferredBuild: true });
    const controller = createSceneController(harness.options);
    const first = controller.start();
    controller.pause();
    const second = controller.resume();

    harness.resolveBuild(0);
    harness.resolveBuild(1);
    await Promise.all([first, second]);

    expect(harness.generations[0]?.dispose).toHaveBeenCalledOnce();
    expect(harness.generations[1]?.dispose).not.toHaveBeenCalled();
    expect(controller.snapshot()).toMatchObject({ currentGeneration: 2, canvasCount: 1, rafCount: 1 });
  });

  it.each(['loading', 'running', 'paused'] as const)('handles first context loss from retained %s state', async (source) => {
    const harness = createHarness({ deferredBuild: source === 'loading' });
    const controller = createSceneController(harness.options);
    const start = controller.start();
    if (source !== 'loading') await start;
    if (source === 'paused') controller.pause();
    const event = new Event('webglcontextlost', { cancelable: true });

    harness.canvas.dispatchEvent(event);

    expect(event.defaultPrevented).toBe(true);
    expect(controller.snapshot()).toMatchObject({
      state: { kind: 'lost', lostAt: 0, restorationPending: false },
      rafCount: 0,
      currentGeneration: null,
    });
    if (source === 'loading') {
      expect(harness.buildContexts[0]?.signal.aborted).toBe(true);
      harness.resolveBuild(0);
      await start;
    }
    expect(harness.generations[0]?.dispose).toHaveBeenCalledOnce();
  });

  it('rejects context loss from a pause without a retained context', () => {
    const harness = createHarness({ deferredBuild: true });
    const controller = createSceneController(harness.options);
    void controller.start();
    controller.pause();

    harness.canvas.dispatchEvent(new Event('webglcontextlost', { cancelable: true }));

    expect(controller.snapshot().state).toEqual({ kind: 'paused', generation: null, resumeNeedsLoad: true });
  });

  it('defers a hidden restoration and restores on the first visible lifecycle task before cutoff', async () => {
    const harness = createHarness();
    const controller = createSceneController(harness.options);
    await controller.start();
    harness.page.visibilityState = 'hidden';
    harness.page.document.dispatchEvent(new Event('visibilitychange'));
    harness.canvas.dispatchEvent(new Event('webglcontextlost', { cancelable: true }));
    harness.clock.now = 2000;
    harness.canvas.dispatchEvent(new Event('webglcontextrestored'));

    expect(controller.snapshot().state).toEqual({ kind: 'lost', lostAt: 0, restorationPending: true });
    expect(harness.buildContexts).toHaveLength(1);

    harness.page.visibilityState = 'visible';
    harness.page.document.dispatchEvent(new Event('visibilitychange'));
    await controller.whenSettled();

    expect(controller.snapshot().state.kind).toBe('running');
    expect(harness.buildContexts).toHaveLength(2);
  });

  it('enters static when hidden restoration is first evaluated after the five-second cutoff', async () => {
    const harness = createHarness();
    const controller = createSceneController(harness.options);
    await controller.start();
    harness.page.visibilityState = 'hidden';
    harness.canvas.dispatchEvent(new Event('webglcontextlost', { cancelable: true }));
    harness.canvas.dispatchEvent(new Event('webglcontextrestored'));
    harness.clock.now = 5000.01;

    harness.page.visibilityState = 'visible';
    harness.page.document.dispatchEvent(new Event('visibilitychange'));
    await controller.whenSettled();

    expect(controller.snapshot()).toMatchObject({ state: { kind: 'static', reason: 'context-restore-timeout' }, rafCount: 0 });
  });

  it('disposes a restoration that finishes after the attach-time cutoff', async () => {
    const harness = createHarness();
    const controller = createSceneController(harness.options);
    await controller.start();
    harness.canvas.dispatchEvent(new Event('webglcontextlost', { cancelable: true }));
    harness.options.build = harness.deferredBuilder();
    harness.clock.now = 1000;
    harness.canvas.dispatchEvent(new Event('webglcontextrestored'));
    expect(controller.snapshot().state.kind).toBe('restoring');
    harness.clock.now = 5001;
    harness.resolveBuild(0);
    await controller.whenSettled();

    expect(harness.generations[1]?.dispose).toHaveBeenCalledOnce();
    expect(controller.snapshot().state).toEqual({ kind: 'static', reason: 'context-restore-timeout' });
  });

  it('makes a later context loss terminal static after one successful restoration', async () => {
    const harness = createHarness();
    const controller = createSceneController(harness.options);
    await controller.start();
    harness.canvas.dispatchEvent(new Event('webglcontextlost', { cancelable: true }));
    harness.canvas.dispatchEvent(new Event('webglcontextrestored'));
    await controller.whenSettled();

    harness.canvas.dispatchEvent(new Event('webglcontextlost', { cancelable: true }));

    expect(controller.snapshot().state).toEqual({ kind: 'static', reason: 'repeated-context-loss' });
  });

  it.each([
    ['idle', 'idle'],
    ['loading', 'paused'],
    ['running', 'paused'],
    ['paused', 'paused'],
    ['static', 'static'],
  ] as const)('freezes %s without creating work and restores according to the BFCache table', async (source, frozenKind) => {
    const harness = createHarness({ deferredBuild: source === 'loading' });
    const controller = createSceneController(harness.options);
    let start: Promise<void> | undefined;
    if (source !== 'idle') start = controller.start();
    if (source !== 'idle' && source !== 'loading') await start;
    if (source === 'paused') controller.pause();
    if (source === 'static') controller.setStatic('test');

    harness.page.window.dispatchEvent(pageEvent('pagehide', true));
    expect(controller.snapshot()).toMatchObject({ overlay: 'frozen', state: { kind: frozenKind }, rafCount: 0 });
    const beforeShow = harness.buildContexts.length;
    harness.page.window.dispatchEvent(pageEvent('pageshow', true));
    if (source === 'loading') harness.resolveBuild(1);
    await controller.whenSettled();

    expect(controller.snapshot().overlay).toBe('active');
    if (source === 'running') expect(controller.snapshot().state.kind).toBe('running');
    if (source === 'paused') {
      expect(controller.snapshot()).toMatchObject({
        state: { kind: 'paused', generation: 1, resumeNeedsLoad: false },
        currentGeneration: 1,
        rafCount: 0,
      });
      expect(harness.generations[0]?.dispose).not.toHaveBeenCalled();
    }
    if (source === 'loading') expect(harness.buildContexts.length).toBe(beforeShow + 1);
    if (source === 'static') expect(controller.snapshot().state.kind).toBe('static');
    if (start && source === 'loading') {
      harness.resolveBuild(0);
      await start;
    }
  });

  it('freezes restoration back to lost and applies the original cutoff on pageshow', async () => {
    const harness = createHarness();
    const controller = createSceneController(harness.options);
    await controller.start();
    harness.canvas.dispatchEvent(new Event('webglcontextlost', { cancelable: true }));
    harness.options.build = harness.deferredBuilder();
    harness.canvas.dispatchEvent(new Event('webglcontextrestored'));
    harness.page.window.dispatchEvent(pageEvent('pagehide', true));
    expect(controller.snapshot()).toMatchObject({ overlay: 'frozen', state: { kind: 'lost', lostAt: 0 } });
    harness.clock.now = 5001;

    harness.page.window.dispatchEvent(pageEvent('pageshow', true));
    await controller.whenSettled();

    expect(controller.snapshot().state).toEqual({ kind: 'static', reason: 'context-restore-timeout' });
  });

  it('does not attach a completion while frozen', async () => {
    const harness = createHarness({ deferredBuild: true });
    const controller = createSceneController(harness.options);
    const start = controller.start();
    harness.page.window.dispatchEvent(pageEvent('pagehide', true));
    harness.resolveBuild(0);
    await start;

    expect(controller.snapshot()).toMatchObject({ overlay: 'frozen', currentGeneration: null, rafCount: 0 });
    expect(harness.generations[0]?.dispose).toHaveBeenCalledOnce();
  });

  it('makes non-persisted pagehide and disposal terminal and idempotent', async () => {
    const harness = createHarness();
    const controller = createSceneController(harness.options);
    await controller.start();

    harness.page.window.dispatchEvent(pageEvent('pagehide', false));
    controller.dispose();
    harness.page.window.dispatchEvent(pageEvent('pageshow', true));

    expect(controller.snapshot()).toMatchObject({ overlay: 'disposed', state: { kind: 'disposed' }, canvasCount: 0, rafCount: 0 });
    expect(harness.generations[0]?.dispose).toHaveBeenCalledOnce();
    await expect(controller.start()).resolves.toBeUndefined();
    expect(controller.snapshot().state.kind).toBe('disposed');
  });

  it('restarts with a new generation when quality changes and applies tier settings', async () => {
    const harness = createHarness();
    const controller = createSceneController(harness.options);
    await controller.start();

    await controller.setQuality('low');

    expect(harness.buildContexts.map((context) => context.quality)).toEqual(['high', 'low']);
    expect(harness.generations[0]?.dispose).toHaveBeenCalledOnce();
    expect(controller.snapshot()).toMatchObject({ state: { kind: 'running', generation: 2 }, quality: 'low' });
  });
});

function createHarness(options: { deferredBuild?: boolean } = {}) {
  const clock = { now: 0 };
  const scheduler = new FakeScheduler(clock);
  const canvas = new EventTarget();
  const page = {
    document: new EventTarget(),
    window: new EventTarget(),
    visibilityState: 'visible' as DocumentVisibilityState,
  };
  const generations: Array<SceneGeneration & { render: ReturnType<typeof vi.fn>; dispose: ReturnType<typeof vi.fn> }> = [];
  const buildContexts: SceneBuildContext[] = [];
  const pending: Array<((generation: SceneGeneration) => void) | undefined> = [];

  const makeGeneration = (): SceneGeneration & { render: ReturnType<typeof vi.fn>; dispose: ReturnType<typeof vi.fn> } => {
    const generation = { render: vi.fn(), dispose: vi.fn() };
    generations.push(generation);
    return generation;
  };
  const deferredBuilder = () => (context: SceneBuildContext): Promise<SceneGeneration> => {
    buildContexts.push(context);
    return new Promise((resolve) => pending.push(resolve));
  };
  const immediateBuilder = async (context: SceneBuildContext): Promise<SceneGeneration> => {
    buildContexts.push(context);
    return makeGeneration();
  };
  const controllerOptions = {
    canvas,
    quality: 'high' as const,
    scheduler,
    page,
    motionAllowed: () => true,
    build: options.deferredBuild ? deferredBuilder() : immediateBuilder,
  };

  return {
    clock,
    scheduler,
    canvas,
    page,
    generations,
    buildContexts,
    options: controllerOptions,
    deferredBuilder,
    resolveBuild(index: number) {
      const resolve = pending[index];
      if (!resolve) throw new Error(`No pending build ${index}`);
      resolve(makeGeneration());
    },
  };
}

class FakeScheduler implements SceneScheduler {
  private nextId = 1;
  private frames = new Map<number, FrameRequestCallback>();
  private timers = new Map<number, { callback: () => void; dueAt: number }>();

  constructor(private readonly clock: { now: number }) {}

  now = () => this.clock.now;
  requestAnimationFrame = (callback: FrameRequestCallback): number => {
    const id = this.nextId++;
    this.frames.set(id, callback);
    return id;
  };
  cancelAnimationFrame = (id: number): void => { this.frames.delete(id); };
  setTimeout = (callback: () => void, delay: number): number => {
    const id = this.nextId++;
    this.timers.set(id, { callback, dueAt: this.clock.now + delay });
    return id;
  };
  clearTimeout = (id: number): void => { this.timers.delete(id); };

  flushFrame(now: number): void {
    this.clock.now = now;
    const entries = [...this.frames.entries()];
    this.frames.clear();
    for (const [, callback] of entries) callback(now);
  }

  flushTimers(now: number): void {
    this.clock.now = now;
    const due = [...this.timers.entries()]
      .filter(([, timer]) => timer.dueAt <= now)
      .sort((left, right) => left[1].dueAt - right[1].dueAt);
    for (const [id, timer] of due) {
      if (!this.timers.delete(id)) continue;
      timer.callback();
    }
  }
}

function pageEvent(type: string, persisted: boolean): Event {
  const event = new Event(type);
  Object.defineProperty(event, 'persisted', { value: persisted });
  return event;
}

function journey(overrides: Partial<JourneySnapshot> = {}): JourneySnapshot {
  return {
    scrollY: 0,
    routeProgress: 0,
    direction: 0,
    acceleration: 0,
    driveSpeed: 0.18,
    activeSectionId: 'start',
    chapter: 'deep-night',
    sign: null,
    arrived: false,
    ...overrides,
  };
}