/**
 * Single Page Application Styles
 * Custom styles for SPA functionality including collapsible sections,
 * animations, progress indicators, and responsive layouts
 * 
 * @author Youcheng Li
 * @version 1.0.0
 */

/* ========================================
   Progress Indicator
   ======================================== */

.scroll-progress {
  position: fixed;
  top: 0;
  left: 0;
  width: 0%;
  height: 3px;
  background: linear-gradient(90deg, var(--primary-color), var(--primary-light));
  z-index: 9999;
  transition: width 0.25s ease;
  box-shadow: 0 0 10px rgba(var(--primary-rgb), 0.5);
}

/* ========================================
   Back to Top Button Enhanced
   ======================================== */

.back-to-top {
  position: fixed;
  bottom: 20px;
  right: 20px;
  width: 50px;
  height: 50px;
  background: var(--primary-color);
  color: white;
  border: none;
  border-radius: 50%;
  font-size: 18px;
  cursor: pointer;
  opacity: 0;
  visibility: hidden;
  transform: translateY(20px);
  transition: all var(--transition-base);
  z-index: 1000;
  box-shadow: var(--shadow-lg);
}

.back-to-top:hover {
  background: var(--primary-dark);
  transform: translateY(0) scale(1.05);
  transition: all var(--transition-base);
}

.back-to-top.visible {
  opacity: 1;
  visibility: visible;
  transform: translateY(0);
}

/* ========================================
   Collapsible Sections
   ======================================== */

.collapsible-content {
  overflow: hidden;
  transition: max-height var(--transition-slow) ease;
}

.collapsible-content.collapsed {
  max-height: 0 !important;
}

.collapse-toggle {
  background: none;
  border: none;
  color: var(--primary-color);
  font-weight: 600;
  cursor: pointer;
  display: flex;
  align-items: center;
  gap: var(--space-2);
  transition: all var(--transition-fast);
}

.collapse-toggle:hover {
  color: var(--primary-dark);
}

.collapse-toggle i {
  transition: transform var(--transition-base);
}

/* ========================================
   Timeline Enhancements (News Section)
   ======================================== */

.timeline {
  position: relative;
  padding-left: 30px;
}

.timeline::before {
  content: '';
  position: absolute;
  left: 0;
  top: 0;
  bottom: 0;
  width: 2px;
  background: linear-gradient(180deg, var(--primary-color), var(--primary-light));
}

.timeline-item {
  position: relative;
  margin-bottom: var(--space-6);
  opacity: 1;
  transform: translateX(0);
  transition: all var(--transition-base);
}

.timeline-item::before {
  content: '';
  position: absolute;
  left: -34px;
  top: 30px;
  width: 10px;
  height: 10px;
  border-radius: 50%;
  background: var(--primary-color);
  border: 2px solid var(--bg-primary);
  box-shadow: 0 0 0 4px var(--bg-secondary);
  transition: all var(--transition-base);
}

.timeline-item:hover::before {
  transform: scale(1.2);
  box-shadow: 0 0 0 6px var(--bg-secondary), 0 0 20px rgba(var(--primary-rgb), 0.3);
}

.timeline-item.hidden-news {
  margin-bottom: 0;
}

.expand-news-btn {
  margin-top: var(--space-4);
  width: 100%;
  justify-content: center;
  gap: var(--space-2);
}

/* ========================================
   Project Cards and Filters
   ======================================== */

.filter-buttons {
  display: flex;
  gap: var(--space-2);
  flex-wrap: wrap;
  margin-bottom: var(--space-6);
  justify-content: center;
}

.filter-btn {
  padding: var(--space-2) var(--space-4);
  font-size: var(--text-sm);
  border: 2px solid var(--border-color);
  background: transparent;
  transition: all var(--transition-base);
  position: relative;
  overflow: hidden;
}

.filter-btn::before {
  content: '';
  position: absolute;
  top: 0;
  left: -100%;
  width: 100%;
  height: 100%;
  background: var(--primary-color);
  transition: left var(--transition-base);
  z-index: -1;
}

.filter-btn:hover::before,
.filter-btn.active::before {
  left: 0;
}

.filter-btn:hover,
.filter-btn.active {
  color: white;
  border-color: var(--primary-color);
  transform: translateY(-2px);
}

.projects-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(350px, 1fr));
  gap: var(--space-6);
  margin-bottom: var(--space-10);
}

.project-card {
  height: 100%;
  overflow: hidden;
  transition: all var(--transition-base);
  position: relative;
}

.project-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: -100%;
  width: 100%;
  height: 2px;
  background: linear-gradient(90deg, var(--primary-color), var(--primary-light));
  transition: left var(--transition-slow);
}

.project-card:hover::before {
  left: 0;
}

.project-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-xl);
  transition: all var(--transition-base);
}

/* Project Image Styles */
.project-image {
  width: 100%;
  height: 200px;
  overflow: hidden;
  background: var(--bg-tertiary);
  border-radius: var(--radius-lg) var(--radius-lg) 0 0;
  display: flex;
  align-items: center;
  justify-content: center;
  margin-bottom: var(--space-3);
}

.project-image img {
  width: 100%;
  height: 100%;
  object-fit: cover;
  transition: transform var(--transition-base);
}

.project-card:hover .project-image img {
  transform: scale(1.05);
}

.expand-project-btn {
  color: var(--primary-color);
  text-decoration: none;
  font-size: var(--text-sm);
  padding: 0;
  background: none;
  border: none;
}

.expand-project-btn:hover {
  color: var(--primary-dark);
  text-decoration: underline;
}

/* ========================================
   Publications Section
   ======================================== */

.year-filter {
  display: flex;
  gap: var(--space-3);
  margin-bottom: var(--space-6);
  justify-content: center;
  flex-wrap: wrap;
}

.year-badge {
  padding: var(--space-2) var(--space-4);
  background: var(--bg-tertiary);
  border: 2px solid transparent;
  border-radius: var(--radius-full);
  cursor: pointer;
  transition: all var(--transition-fast);
  font-weight: 500;
  position: relative;
  overflow: hidden;
}

.year-badge::before {
  content: '';
  position: absolute;
  top: 0;
  left: -100%;
  width: 100%;
  height: 100%;
  background: var(--primary-color);
  transition: left var(--transition-base);
  z-index: -1;
}

.year-badge:hover::before,
.year-badge.active::before {
  left: 0;
}

.year-badge:hover,
.year-badge.active {
  color: white;
  border-color: var(--primary-color);
  transform: translateY(-2px);
}

.year-header {
  font-size: var(--text-2xl);
  font-weight: 700;
  margin-bottom: var(--space-4);
  color: var(--primary-color);
  padding-bottom: var(--space-2);
  border-bottom: 2px solid var(--border-color);
  display: flex;
  align-items: center;
  justify-content: space-between;
  transition: all var(--transition-base);
}

.year-header:hover {
  color: var(--primary-dark);
}

.toggle-icon {
  transition: transform var(--transition-base);
  font-size: var(--text-lg);
}

.publication-item {
  margin-bottom: var(--space-4);
  transition: all var(--transition-base);
  border-left: 3px solid transparent;
}

.publication-item:hover {
  transform: translateX(8px);
  border-left-color: var(--primary-color);
}

/* ========================================
   Teaching and Course Cards
   ======================================== */

.course-card {
  margin-bottom: var(--space-4);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  overflow: hidden;
  transition: all var(--transition-base);
}

.course-card:hover {
  box-shadow: var(--shadow-lg);
  border-color: var(--primary-light);
}

.course-header {
  padding: var(--space-4);
  background: var(--bg-tertiary);
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: space-between;
  transition: all var(--transition-base);
}

.course-header:hover {
  background: var(--primary-light);
  color: white;
}

.course-details {
  padding: var(--space-4);
  border-top: 1px solid var(--border-color);
  display: none;
}

.course-materials {
  margin-top: var(--space-3);
}

.material-item {
  padding: var(--space-2);
  background: var(--bg-secondary);
  margin-bottom: var(--space-2);
  border-radius: var(--radius-md);
  border-left: 3px solid var(--primary-color);
}

/* ========================================
   Talks Section
   ======================================== */

.talk-item {
  padding: var(--space-4);
  margin-bottom: var(--space-3);
  background: var(--bg-secondary);
  border-radius: var(--radius-lg);
  border-left: 4px solid var(--primary-color);
  transition: all var(--transition-base);
}

.talk-item:hover {
  transform: translateX(4px);
  box-shadow: var(--shadow-md);
}

.talk-type-badge {
  display: inline-block;
  padding: var(--space-1) var(--space-2);
  font-size: var(--text-xs);
  border-radius: var(--radius-full);
  font-weight: 600;
  text-transform: uppercase;
}

.talk-type-badge.invited {
  background: var(--success-light);
  color: var(--success-dark);
}

.talk-type-badge.conference {
  background: var(--primary-light);
  color: white;
}

.expand-talks-btn {
  margin-top: var(--space-4);
  width: 100%;
  justify-content: center;
  gap: var(--space-2);
}

/* ========================================
   Resources Section
   ======================================== */

.resource-category {
  margin-bottom: var(--space-6);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  overflow: hidden;
}

.category-header {
  padding: var(--space-4);
  background: var(--bg-tertiary);
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: space-between;
  font-weight: 600;
  transition: all var(--transition-base);
}

.category-header:hover {
  background: var(--primary-light);
  color: white;
}

.resource-items {
  padding: var(--space-4);
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
  gap: var(--space-4);
}

.resource-item {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  padding: var(--space-3);
  background: var(--bg-secondary);
  border-radius: var(--radius-md);
  text-decoration: none;
  color: var(--text-primary);
  transition: all var(--transition-base);
}

.resource-item:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
  color: var(--primary-color);
  text-decoration: none;
}

.resource-icon {
  width: 32px;
  height: 32px;
  border-radius: var(--radius-md);
  flex-shrink: 0;
}

/* ========================================
   Animations and Transitions
   ======================================== */

.fade-in {
  animation: fadeIn 0.6s ease forwards;
}

.slide-in-up {
  animation: slideInUp 0.6s ease forwards;
}

.scale-in {
  animation: scaleIn 0.4s ease forwards;
}

@keyframes fadeIn {
  from {
    opacity: 0;
    transform: translateY(20px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes slideInUp {
  from {
    opacity: 0;
    transform: translateY(30px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes scaleIn {
  from {
    opacity: 0;
    transform: scale(0.9);
  }
  to {
    opacity: 1;
    transform: scale(1);
  }
}

/* Stagger animation for lists */
.stagger-animation > * {
  opacity: 0;
  transform: translateY(20px);
  animation: fadeIn 0.6s ease forwards;
}

.stagger-animation > *:nth-child(1) { animation-delay: 0s; }
.stagger-animation > *:nth-child(2) { animation-delay: 0.1s; }
.stagger-animation > *:nth-child(3) { animation-delay: 0.2s; }
.stagger-animation > *:nth-child(4) { animation-delay: 0.3s; }
.stagger-animation > *:nth-child(5) { animation-delay: 0.4s; }
.stagger-animation > *:nth-child(6) { animation-delay: 0.5s; }

/* ========================================
   Scroll Animations
   ======================================== */

.animate-on-scroll {
  opacity: 0;
  transform: translateY(30px);
  transition: all 0.8s cubic-bezier(0.25, 0.46, 0.45, 0.94);
}

.animate-on-scroll.animated {
  opacity: 1;
  transform: translateY(0);
}

/* ========================================
   Responsive Design
   ======================================== */

@media (max-width: 1200px) {
  .projects-grid {
    grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  }
  
  .resource-items {
    grid-template-columns: repeat(auto-fill, minmax(200px, 1fr));
  }
}

@media (max-width: 768px) {
  .back-to-top {
    bottom: 15px;
    right: 15px;
    width: 45px;
    height: 45px;
    font-size: 16px;
  }
  
  .filter-buttons {
    justify-content: center;
  }
  
  .projects-grid {
    grid-template-columns: 1fr;
    gap: var(--space-4);
  }
  
  .year-filter {
    justify-content: center;
    gap: var(--space-2);
  }
  
  .year-badge {
    padding: var(--space-2) var(--space-3);
    font-size: var(--text-sm);
  }
  
  .resource-items {
    grid-template-columns: 1fr;
  }
  
  .timeline {
    padding-left: 20px;
  }
  
  .timeline-item::before {
    left: -24px;
  }
  
  .course-header {
    padding: var(--space-3);
  }
  
  .course-details {
    padding: var(--space-3);
  }
}

@media (max-width: 480px) {
  .filter-btn,
  .year-badge {
    font-size: var(--text-xs);
    padding: var(--space-1) var(--space-3);
  }
  
  .expand-news-btn,
  .expand-talks-btn {
    font-size: var(--text-sm);
    padding: var(--space-2) var(--space-3);
  }
}

/* ========================================
   Mobile View Adjustments
   ======================================== */

.mobile-view .timeline {
  padding-left: 15px;
}

.mobile-view .timeline-item::before {
  left: -19px;
  width: 8px;
  height: 8px;
}

.mobile-view .project-card:hover {
  transform: none;
}

.mobile-view .publication-item:hover {
  transform: translateX(4px);
}

/* ========================================
   Dark Mode Adjustments
   ======================================== */

[data-theme="dark"] .scroll-progress {
  box-shadow: 0 0 10px rgba(var(--primary-rgb), 0.7);
}

[data-theme="dark"] .timeline::before {
  background: linear-gradient(180deg, var(--primary-light), var(--primary-color));
}

[data-theme="dark"] .filter-btn,
[data-theme="dark"] .year-badge {
  background: var(--bg-tertiary);
  border-color: var(--border-color);
}

[data-theme="dark"] .resource-item:hover {
  background: var(--bg-tertiary);
}

/* ========================================
   Section Spacing
   ======================================== */
section {
  margin-bottom: var(--space-16);
}

section + section {
  margin-top: var(--space-12);
}

/* ========================================
   Citation Count Styles
   ======================================== */
.citation-count {
  display: inline-flex;
  align-items: center;
  gap: var(--space-1);
  font-size: var(--text-sm);
  color: var(--text-tertiary);
  font-weight: 500;
  margin-top: var(--space-2);
}

.citation-count i {
  color: var(--primary-color);
}

/* ========================================
   Publication Links Spacing
   ======================================== */
.publication-links {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2);
  align-items: center;
}

.publication-links .btn {
  margin-right: 0; /* Remove default margin since we use gap */
}

/* ========================================
   Loading and Lazy Loading
   ======================================== */

img[data-src] {
  opacity: 0;
  transition: opacity var(--transition-base);
}

img.loaded {
  opacity: 1;
}

.loading-skeleton {
  background: linear-gradient(90deg, var(--bg-secondary) 25%, var(--bg-tertiary) 50%, var(--bg-secondary) 75%);
  background-size: 200% 100%;
  animation: loading 1.5s infinite;
}

@keyframes loading {
  0% {
    background-position: 200% 0;
  }
  100% {
    background-position: -200% 0;
  }
}

/* ========================================
   Navigation Highlight Effect
   ======================================== */
.section-highlight {
  animation: sectionFlash 1.5s ease-out;
}

@keyframes sectionFlash {
  0% {
    background-color: transparent;
    box-shadow: none;
  }
  15% {
    background-color: rgba(var(--primary-rgb), 0.1);
    box-shadow: 0 0 20px rgba(var(--primary-rgb), 0.3);
  }
  100% {
    background-color: transparent;
    box-shadow: none;
  }
}

[data-theme="dark"] .section-highlight {
  animation: sectionFlashDark 1.5s ease-out;
}

@keyframes sectionFlashDark {
  0% {
    background-color: transparent;
    box-shadow: none;
  }
  15% {
    background-color: rgba(96, 165, 250, 0.15);
    box-shadow: 0 0 25px rgba(96, 165, 250, 0.4);
  }
  100% {
    background-color: transparent;
    box-shadow: none;
  }
}

/* ========================================
   Accessibility Improvements
   ======================================== */

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

/* Focus indicators */
.collapse-toggle:focus,
.filter-btn:focus,
.year-badge:focus,
.back-to-top:focus {
  outline: 2px solid var(--primary-color);
  outline-offset: 2px;
}

/* Reduced motion support */
@media (prefers-reduced-motion: reduce) {
  .animate-on-scroll,
  .timeline-item,
  .project-card,
  .publication-item,
  .talk-item,
  .resource-item,
  .back-to-top,
  .toggle-icon {
    transition: none;
    animation: none;
  }
  
  .fade-in,
  .slide-in-up,
  .scale-in,
  .stagger-animation > * {
    animation: none;
    opacity: 1;
    transform: none;
  }
}