/* ========================================================================
   StudyMate AI — Skeleton Loading System
   Reusable, theme-aware, accessible, performance-optimized
   ======================================================================== */

/* ---------------------------------------------------------------------------
   Shimmer Animation
   --------------------------------------------------------------------------- */

@keyframes skeletonShimmer {
  0% {
    background-position: -400px 0;
  }
  100% {
    background-position: 400px 0;
  }
}

/* ---------------------------------------------------------------------------
   Base Skeleton Element
   All skeleton primitives extend this. Uses existing theme CSS variables
   for automatic dark/light/blue/purple support.
   --------------------------------------------------------------------------- */

.skeleton {
  background: var(--surface-strong, rgba(255, 255, 255, 0.08));
  background-image: linear-gradient(
    90deg,
    var(--surface-strong, rgba(255, 255, 255, 0.08)) 0%,
    rgba(255, 255, 255, 0.06) 40%,
    var(--surface-strong, rgba(255, 255, 255, 0.08)) 80%
  );
  background-size: 800px 100%;
  background-repeat: no-repeat;
  animation: skeletonShimmer 1.6s ease-in-out infinite;
  border-radius: 8px;
  pointer-events: none;
}

/* Light theme shimmer adjustment */
body.light .skeleton {
  background: var(--surface-strong, rgba(15, 23, 42, 0.08));
  background-image: linear-gradient(
    90deg,
    var(--surface-strong, rgba(15, 23, 42, 0.08)) 0%,
    rgba(15, 23, 42, 0.04) 40%,
    var(--surface-strong, rgba(15, 23, 42, 0.08)) 80%
  );
  background-size: 800px 100%;
  background-repeat: no-repeat;
  animation: skeletonShimmer 1.6s ease-in-out infinite;
}

/* ---------------------------------------------------------------------------
   Prefers Reduced Motion
   Disables shimmer animation for accessibility; uses static opacity pulse.
   --------------------------------------------------------------------------- */

@media (prefers-reduced-motion: reduce) {
  .skeleton {
    animation: none;
    background-image: none;
  }
}

/* ---------------------------------------------------------------------------
   Skeleton Primitives
   --------------------------------------------------------------------------- */

/* Text line placeholder */
.skeleton-text {
  height: 14px;
  width: 100%;
  margin-bottom: 10px;
  border-radius: 6px;
}

.skeleton-text.short {
  width: 60%;
}

.skeleton-text.xs {
  width: 40%;
}

.skeleton-text.lg {
  height: 20px;
}

.skeleton-text.xl {
  height: 28px;
}

/* Card block placeholder */
.skeleton-card {
  width: 100%;
  min-height: 80px;
  border-radius: 18px;
  margin-bottom: 12px;
}

/* Circular avatar placeholder */
.skeleton-avatar {
  width: 40px;
  height: 40px;
  border-radius: 50%;
  flex-shrink: 0;
}

.skeleton-avatar.lg {
  width: 64px;
  height: 64px;
}

.skeleton-avatar.sm {
  width: 28px;
  height: 28px;
}

/* Button placeholder */
.skeleton-btn {
  height: 44px;
  width: 100%;
  border-radius: 999px;
}

.skeleton-btn.sm {
  height: 36px;
  width: 120px;
}

/* Image placeholder */
.skeleton-image {
  width: 100%;
  height: 200px;
  border-radius: var(--radius-md, 18px);
}

/* Input field placeholder */
.skeleton-input {
  height: 48px;
  width: 100%;
  border-radius: 16px;
}

/* Toggle placeholder */
.skeleton-toggle {
  width: 44px;
  height: 24px;
  border-radius: 12px;
  flex-shrink: 0;
}

/* Dropdown placeholder */
.skeleton-dropdown {
  height: 42px;
  width: 120px;
  border-radius: 12px;
}

/* Sidebar label placeholder */
.skeleton-label {
  height: 12px;
  width: 80px;
  border-radius: 4px;
  margin-bottom: 12px;
}

/* Small icon placeholder */
.skeleton-icon {
  width: 22px;
  height: 22px;
  border-radius: 6px;
  flex-shrink: 0;
}

/* Nav item placeholder (settings page) */
.skeleton-nav-item {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 14px 16px;
  border-radius: 14px;
  background: var(--surface-soft, rgba(255, 255, 255, 0.05));
}

.skeleton-nav-item .skeleton-icon {
  width: 18px;
  height: 18px;
}

.skeleton-nav-text {
  display: flex;
  flex-direction: column;
  gap: 6px;
  flex: 1;
}

/* ---------------------------------------------------------------------------
   Skeleton Row Helpers
   --------------------------------------------------------------------------- */

.skeleton-row {
  display: flex;
  align-items: center;
  gap: 12px;
}

.skeleton-col {
  display: flex;
  flex-direction: column;
  gap: 8px;
  flex: 1;
  min-width: 0;
}

.skeleton-row-between {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  padding: 14px 0;
}

.skeleton-row-between + .skeleton-row-between {
  border-top: 1px solid var(--border, rgba(255, 255, 255, 0.1));
}

/* ---------------------------------------------------------------------------
   Page-Level Skeleton Overlays
   Positioned absolutely over real content. Fade out when content is ready.
   --------------------------------------------------------------------------- */

.skeleton-overlay {
  position: absolute;
  inset: 0;
  z-index: 900;
  opacity: 1;
  transition: opacity 0.3s ease;
}

/* Full-screen variant for pages without relative parent */
.skeleton-overlay--fullscreen {
  position: fixed;
}

.skeleton-overlay.skeleton-hidden {
  opacity: 0;
  pointer-events: none;
}

/* ---------------------------------------------------------------------------
   Dashboard Skeleton Layout
   --------------------------------------------------------------------------- */

.skel-dashboard {
  display: flex;
  height: 100%;
  gap: 18px;
  padding: 18px;
  background:
    radial-gradient(circle at top left, var(--gradient-top-left, rgba(56, 189, 248, 0.18)), transparent 28%),
    radial-gradient(circle at bottom right, var(--gradient-bottom-right, rgba(14, 165, 233, 0.1)), transparent 24%),
    linear-gradient(140deg, var(--bg-main, #0f172a) 0%, #081120 52%, var(--bg-deep, #020617) 100%);
}

body.light .skel-dashboard {
  background:
    radial-gradient(circle at top left, var(--gradient-top-left), transparent 28%),
    radial-gradient(circle at bottom right, var(--gradient-bottom-right), transparent 24%),
    linear-gradient(140deg, var(--bg-main) 0%, #eef4fb 50%, var(--bg-deep) 100%);
}

body.blue .skel-dashboard {
  background:
    radial-gradient(circle at top left, var(--gradient-top-left), transparent 28%),
    radial-gradient(circle at bottom right, var(--gradient-bottom-right), transparent 24%),
    linear-gradient(140deg, var(--bg-main) 0%, #071428 52%, var(--bg-deep) 100%);
}

body.purple .skel-dashboard {
  background:
    radial-gradient(circle at top left, var(--gradient-top-left), transparent 28%),
    radial-gradient(circle at bottom right, var(--gradient-bottom-right), transparent 24%),
    linear-gradient(140deg, var(--bg-main) 0%, #140830 52%, var(--bg-deep) 100%);
}

/* Sidebar skeleton */
.skel-sidebar {
  width: 260px;
  min-width: 260px;
  padding: 20px;
  display: flex;
  flex-direction: column;
  gap: 18px;
  background: var(--surface, rgba(15, 23, 42, 0.74));
  border: 1px solid var(--border, rgba(255, 255, 255, 0.1));
  border-radius: var(--radius-xl, 28px);
  backdrop-filter: blur(18px);
  -webkit-backdrop-filter: blur(18px);
  box-shadow: var(--shadow-md, 0 18px 55px rgba(2, 6, 23, 0.32));
  overflow: hidden;
}

.skel-sidebar-top {
  display: flex;
  flex-direction: column;
  gap: 18px;
}

.skel-brand {
  display: flex;
  align-items: center;
  gap: 14px;
}

.skel-brand-logo {
  width: 38px;
  height: 38px;
  border-radius: 10px;
}

.skel-brand-text {
  display: flex;
  flex-direction: column;
  gap: 6px;
  flex: 1;
}

.skel-version {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 8px 12px;
  background: var(--surface-soft, rgba(255, 255, 255, 0.05));
  border-radius: 12px;
}

.skel-controls {
  display: flex;
  flex-direction: column;
  gap: 14px;
}

.skel-control-row {
  display: flex;
  align-items: center;
  gap: 6px;
}

.skel-tracker {
  display: flex;
  gap: 16px;
  padding: 10px 12px;
  background: var(--surface-soft, rgba(255, 255, 255, 0.05));
  border-radius: 14px;
}

.skel-tracker-stat {
  display: flex;
  align-items: center;
  gap: 8px;
}

.skel-history {
  flex: 1;
  display: flex;
  flex-direction: column;
  gap: 12px;
  min-height: 0;
  overflow: hidden;
}

.skel-history-card {
  padding: 12px;
  border-radius: 18px;
  background: var(--surface-soft, rgba(255, 255, 255, 0.05));
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.skel-footer {
  margin-top: auto;
  padding-top: 12px;
  border-top: 1px solid var(--border, rgba(255, 255, 255, 0.1));
  display: flex;
  flex-direction: column;
  gap: 12px;
}

/* Main panel skeleton */
.skel-main {
  flex: 1;
  display: flex;
  flex-direction: column;
  min-width: 0;
  min-height: 0;
  overflow: hidden;
  position: relative;
}

.skel-topbar {
  padding: 14px 18px;
  display: flex;
  align-items: center;
  justify-content: flex-end;
  gap: 14px;
}

.skel-chat-area {
  flex: 1;
  display: flex;
  align-items: center;
  justify-content: center;
}

.skel-empty-state {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 12px;
}

.skel-input-bar {
  padding: 12px 18px;
  display: flex;
  align-items: center;
  gap: 12px;
}

.skel-input {
  flex: 1;
  height: 52px;
  border-radius: var(--radius-xl, 28px);
  background: var(--surface, rgba(15, 23, 42, 0.74));
  border: 1px solid var(--border, rgba(255, 255, 255, 0.1));
}

.skel-send-btn {
  width: 42px;
  height: 42px;
  border-radius: 50%;
}

/* ---------------------------------------------------------------------------
   Settings Skeleton Layout
   --------------------------------------------------------------------------- */

.skel-settings {
  min-height: 100dvh;
  display: flex;
  justify-content: center;
  padding: 24px;
  background:
    radial-gradient(circle at top left, var(--gradient-top-left, rgba(56, 189, 248, 0.18)), transparent 28%),
    radial-gradient(circle at bottom right, var(--gradient-bottom-right, rgba(14, 165, 233, 0.1)), transparent 24%),
    linear-gradient(140deg, var(--bg-main, #0f172a) 0%, #081120 52%, var(--bg-deep, #020617) 100%);
}

body.light .skel-settings {
  background:
    radial-gradient(circle at top left, var(--gradient-top-left), transparent 28%),
    radial-gradient(circle at bottom right, var(--gradient-bottom-right), transparent 24%),
    linear-gradient(140deg, var(--bg-main) 0%, #eef4fb 50%, var(--bg-deep) 100%);
}

body.blue .skel-settings {
  background:
    radial-gradient(circle at top left, var(--gradient-top-left), transparent 28%),
    radial-gradient(circle at bottom right, var(--gradient-bottom-right), transparent 24%),
    linear-gradient(140deg, var(--bg-main) 0%, #071428 52%, var(--bg-deep) 100%);
}

body.purple .skel-settings {
  background:
    radial-gradient(circle at top left, var(--gradient-top-left), transparent 28%),
    radial-gradient(circle at bottom right, var(--gradient-bottom-right), transparent 24%),
    linear-gradient(140deg, var(--bg-main) 0%, #140830 52%, var(--bg-deep) 100%);
}

.skel-settings-container {
  width: min(1200px, 100%);
  padding-top: 20px;
}

.skel-settings-header {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  gap: 18px;
  margin-bottom: 32px;
}

.skel-settings-header-info {
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.skel-settings-layout {
  display: grid;
  grid-template-columns: 280px 1fr;
  gap: 32px;
  align-items: start;
}

.skel-settings-nav {
  display: flex;
  flex-direction: column;
  gap: 6px;
}

.skel-settings-content {
  background: var(--surface, rgba(15, 23, 42, 0.74));
  border: 1px solid var(--border, rgba(255, 255, 255, 0.1));
  border-radius: var(--radius-xl, 28px);
  padding: 32px;
  box-shadow: var(--shadow-lg, 0 28px 80px rgba(2, 6, 23, 0.45));
  backdrop-filter: blur(18px);
  -webkit-backdrop-filter: blur(18px);
  display: flex;
  flex-direction: column;
  gap: 24px;
}

.skel-profile-block {
  display: flex;
  align-items: center;
  gap: 18px;
  padding-bottom: 24px;
  border-bottom: 1px solid var(--border, rgba(255, 255, 255, 0.1));
}

.skel-profile-info {
  display: flex;
  flex-direction: column;
  gap: 8px;
  flex: 1;
}

.skel-form-fields {
  display: flex;
  flex-direction: column;
  gap: 20px;
}

.skel-form-group {
  display: flex;
  flex-direction: column;
  gap: 8px;
}

/* ---------------------------------------------------------------------------
   Admin Skeleton (extends base — used by existing admin.html markup)
   --------------------------------------------------------------------------- */

.skel-admin {
  padding: 20px;
  max-width: 1200px;
  margin: 0 auto;
  width: 100%;
  background:
    radial-gradient(circle at top left, var(--gradient-top-left, rgba(56, 189, 248, 0.18)), transparent 28%),
    radial-gradient(circle at bottom right, var(--gradient-bottom-right, rgba(14, 165, 233, 0.1)), transparent 24%),
    linear-gradient(140deg, var(--bg-main, #0f172a) 0%, #081120 52%, var(--bg-deep, #020617) 100%);
}

.skel-admin-grid {
  display: grid;
  grid-template-columns: minmax(0, 1.2fr) minmax(0, 0.8fr);
  gap: 32px;
  margin-top: 32px;
}

.skel-admin-form {
  background: var(--surface-soft, rgba(255, 255, 255, 0.05));
  border: 1px solid var(--border, rgba(255, 255, 255, 0.1));
  border-radius: 20px;
  padding: 24px;
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  display: flex;
  flex-direction: column;
  gap: 24px;
}

.skel-admin-preview {
  display: flex;
  flex-direction: column;
  gap: 12px;
}

.skel-admin-preview-box {
  padding: 24px;
  border-radius: 20px;
  border: 1px dashed var(--border, rgba(255, 255, 255, 0.1));
  min-height: 200px;
  display: flex;
  align-items: center;
  justify-content: center;
}

/* ---------------------------------------------------------------------------
   Mobile Responsive Overrides
   --------------------------------------------------------------------------- */

@media (max-width: 768px) {
  .skel-sidebar {
    display: none;
  }

  .skel-dashboard {
    padding: 0;
    gap: 0;
  }

  .skel-main {
    border-radius: 0;
  }

  .skel-topbar {
    padding: 12px 16px;
  }

  .skel-settings-layout {
    grid-template-columns: 1fr;
    gap: 0;
  }

  .skel-settings-nav {
    gap: 4px;
  }

  .skel-settings-content {
    display: none;
  }

  .skel-admin-grid {
    grid-template-columns: 1fr;
    gap: 20px;
  }
}