/**
 * Vanilla driver for the thinking-orbs canvas engine.
 *
 * The upstream package ships a React component; this module reproduces its
 * behaviour on top of the framework-free engine build vendored under
 * `vendor/thinking-orbs.engine.js` (same-origin, CSP compliant):
 * device-pixel-ratio capped at 2, static frame under reduced motion, and
 * automatic pausing while off-screen or in a hidden tab.
 */

import { resolvePreset, MODE_DRAWS } from '../vendor/thinking-orbs.engine.js';

const REDUCED_MOTION_FRAME = 0.6;

/**
 * Mounts an animated orb on an existing <canvas>.
 * @param {HTMLCanvasElement} canvas
 * @param {{ state?: string, size?: 64|20, theme?: 'light'|'dark', speed?: number }} [options]
 * @returns {{ destroy: () => void, setState: (state: string) => void } | null}
 */
export function mountThinkingOrb(canvas, options = {}) {
  if (!canvas || typeof canvas.getContext !== 'function') return null;

  let state = options.state || 'working';
  const size = options.size === 20 ? 20 : 64;
  const dark = options.theme === 'dark';
  const speedMultiplier = typeof options.speed === 'number' && options.speed > 0 ? options.speed : 1;

  const dpr = Math.min(2, (typeof devicePixelRatio === 'number' && devicePixelRatio) || 1);
  canvas.width = Math.round(size * dpr);
  canvas.height = Math.round(size * dpr);
  canvas.style.width = `${size}px`;
  canvas.style.height = `${size}px`;

  const ctx = canvas.getContext('2d');
  if (!ctx) return null;

  let { mode, speed, opts } = resolvePreset(state, size);
  let draw = MODE_DRAWS[mode];
  let clock = speed * speedMultiplier;

  /**
   * Re-resolves the preset for a new state in place, without tearing down the
   * IntersectionObserver / visibilitychange wiring. A no-op if the state is unchanged.
   * @param {string} nextState
   */
  const applyState = (nextState) => {
    if (!nextState || nextState === state) return;
    state = nextState;
    ({ mode, speed, opts } = resolvePreset(state, size));
    draw = MODE_DRAWS[mode];
    clock = speed * speedMultiplier;
  };
  // Mirrors the current preset name on the canvas as a plain data attribute (no inline style/
  // script involved) so tests can assert the orb's sub-state without reaching into this closure.
  canvas.dataset.orbState = state;
  const setStateAttr = () => { canvas.dataset.orbState = state; };

  const paintAt = (t) => {
    ctx.setTransform(dpr, 0, 0, dpr, 0, 0);
    ctx.clearRect(0, 0, size, size);
    draw(ctx, size, t, dark, opts);
  };

  const reducedMotion = typeof matchMedia === 'function' && matchMedia('(prefers-reduced-motion: reduce)').matches;
  if (reducedMotion) {
    paintAt(REDUCED_MOTION_FRAME);
    return {
      destroy() {},
      setState(nextState) {
        applyState(nextState);
        setStateAttr();
        paintAt(REDUCED_MOTION_FRAME);
      }
    };
  }

  let frameId = 0;
  let running = false;
  let visible = true;

  const tick = () => {
    paintAt((performance.now() / 1000) * clock);
    if (running) frameId = requestAnimationFrame(tick);
  };
  const start = () => {
    if (running) return;
    running = true;
    frameId = requestAnimationFrame(tick);
  };
  const stop = () => {
    running = false;
    cancelAnimationFrame(frameId);
  };

  paintAt((performance.now() / 1000) * clock);

  const observer = typeof IntersectionObserver === 'function'
    ? new IntersectionObserver(([entry]) => {
        visible = entry.isIntersecting;
        if (visible && document.visibilityState !== 'hidden') start();
        else stop();
      })
    : null;
  if (observer) observer.observe(canvas);

  const onVisibilityChange = () => {
    if (document.visibilityState === 'hidden') stop();
    else if (visible) start();
  };
  document.addEventListener('visibilitychange', onVisibilityChange);
  if (!observer) start();

  return {
    destroy() {
      stop();
      if (observer) observer.disconnect();
      document.removeEventListener('visibilitychange', onVisibilityChange);
    },
    /**
     * Switches the orb to a different preset (e.g. `shaping` while queued, `solving` while
     * running) without re-creating the visibility/intersection observers.
     * @param {string} nextState
     */
    setState(nextState) {
      applyState(nextState);
      setStateAttr();
      paintAt((performance.now() / 1000) * clock);
    }
  };
}