/* Shared loading primitives for Bachian Music Class lessons.
   Import with <link rel="stylesheet" href="/shared/loading.css">
   Pairs with /shared/loading.js */

:root {
  --loading-accent: #ff9f43;
  --loading-track: #f0ede8;
}

@keyframes bmc-spin {
  to { transform: rotate(360deg); }
}

.bmc-spinner {
  display: inline-block;
  width: 1em;
  height: 1em;
  border: 0.16em solid var(--loading-track);
  border-top-color: var(--loading-accent);
  border-radius: 50%;
  animation: bmc-spin 0.7s linear infinite;
  vertical-align: -0.15em;
}

/* Button loading state: add/remove the "is-loading" class via
   setButtonLoading() in loading.js. Keeps the button's own width/color,
   just swaps the label for a spinner and blocks re-clicks. */
.is-loading {
  position: relative;
  color: transparent !important;
  pointer-events: none;
}
.is-loading .bmc-spinner {
  position: absolute;
  top: 50%;
  left: 50%;
  margin: -0.5em 0 0 -0.5em;
  color: inherit;
}
.is-loading::before {
  content: "";
  position: absolute;
  inset: 0;
  display: flex;
}

/* Full-screen / full-card loading state: a centered spinner + short label,
   for a wait with no meaningful progress to report (e.g. "送出中...",
   "載入中..."). For asset preloading with real progress, prefer a
   determinate bar (see Peter and the Wolf's preload screen) over this. */
.bmc-loading-block {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 12px;
  padding: 32px 16px;
  color: #888;
  font-size: 0.95rem;
}
.bmc-loading-block .bmc-spinner {
  width: 1.6em;
  height: 1.6em;
  border-width: 0.14em;
}

/* Skeleton placeholder rows for lists that are known to be loading
   (e.g. the leaderboard while submitScore()/fetchLeaderboard() resolve). */
@keyframes bmc-shimmer {
  0% { background-position: -120px 0; }
  100% { background-position: 120px 0; }
}
.bmc-skeleton-row {
  height: 1.1em;
  border-radius: 6px;
  margin-bottom: 8px;
  background: linear-gradient(90deg, var(--loading-track) 25%, #e4e0da 37%, var(--loading-track) 63%);
  background-size: 240px 100%;
  animation: bmc-shimmer 1.2s ease-in-out infinite;
}

@media (prefers-reduced-motion: reduce) {
  .bmc-spinner { animation-duration: 1.6s; }
  .bmc-skeleton-row { animation: none; background: var(--loading-track); }
}