// SPDX-License-Identifier: AGPL-3.0-or-later

// The shield: what covers the screen while the panel is dark.
//
// This manages the wake gesture: a double tap wake.

// Above the dusk veil (9000), which is itself above --z-modal: the fade may
// still be running when the panel is cut.
const SHIELD_Z_INDEX = 9500;

// Two taps inside this window, and this far apart at most, count as a double
// tap.
const DOUBLE_TAP_MS = 500;
const DOUBLE_TAP_SLOP_PX = 80;

let shield = null;
let lastTap = null;
let wakeAction = null;

/**
 * Cover the screen. Idempotent; the first caller's `onWake` stands.
 *
 * @param {object} [options]
 * @param {Function} [options.onWake] Run when the user double taps.
 */
export function raiseShield({ onWake } = {}) {
  if (shield) {
    return;
  }
  lastTap = null;
  wakeAction = onWake ?? null;

  shield = document.createElement("div");
  shield.className = "screen-shield";
  shield.style.cssText = [
    "position: fixed",
    "inset: 0",
    `z-index: ${SHIELD_Z_INDEX}`,
    // Transparent: the dusk veil and the screen-off effect do the visuals.
    // This element exists only to catch input.
    "background: transparent",
    // Servo ignores touch-action, so the handlers below are what actually stop
    // the gesture. Declared anyway for correctness elsewhere.
    "touch-action: none",
  ].join(";");

  // Capture phase, and every pointer/touch stage: a swallowed `down` whose
  // `move` and `up` still landed would leave the page mid-gesture.
  for (const type of [
    "pointerdown",
    "pointermove",
    "pointerup",
    "pointercancel",
    "touchstart",
    "touchmove",
    "touchend",
    "touchcancel",
    "click",
    "dblclick",
    "contextmenu",
    "wheel",
  ]) {
    shield.addEventListener(type, swallow, true);
  }
  shield.addEventListener("pointerup", onTap, true);

  document.body.appendChild(shield);
}

// Uncover the screen. Idempotent.
export function lowerShield() {
  shield?.remove();
  shield = null;
  lastTap = null;
  wakeAction = null;
}

// True while the shield is up, i.e. while the screen is meant to be dark.
export function shieldIsUp() {
  return shield !== null;
}

function swallow(event) {
  event.preventDefault();
  event.stopPropagation();
}

// A double tap wakes. Tracked on pointerup rather than pointerdown so a press
// that turns into a drag does not count as a tap.
function onTap(event) {
  const now = event.timeStamp;
  const previous = lastTap;
  lastTap = { x: event.clientX, y: event.clientY, at: now };

  if (
    previous &&
    now - previous.at <= DOUBLE_TAP_MS &&
    Math.abs(event.clientX - previous.x) <= DOUBLE_TAP_SLOP_PX &&
    Math.abs(event.clientY - previous.y) <= DOUBLE_TAP_SLOP_PX
  ) {
    const wake = wakeAction;
    lowerShield();
    wake?.();
  }
}