/**
 * Snap-Study Design System
 * See docs/DESIGN_SYSTEM.md for full documentation
 */

/* ==========================================================================
   1. CSS Variables (Design Tokens)
   ========================================================================== */

:root {
  /* Primary Colors */
  --color-primary: #2563eb;
  --color-primary-hover: #1d4ed8;
  --color-secondary: #1e293b;
  --color-accent: #fc3f1d;
  --color-accent-hover: #e53517;

  /* Semantic Colors */
  --color-success: #16a34a;
  --color-success-bg: #f0fdf4;
  --color-success-border: #bbf7d0;
  --color-error: #dc2626;
  --color-error-bg: #fef2f2;
  --color-error-border: #fecaca;
  --color-warning: #d97706;
  --color-warning-bg: #fffbeb;
  --color-warning-border: #fde68a;
  --color-info: #0284c7;
  --color-info-bg: #f0f9ff;
  --color-info-border: #bae6fd;

  /* Neutral Colors */
  --color-bg: #f8fafc;
  --color-surface: #ffffff;
  --color-border: #e2e8f0;
  --color-border-strong: #cbd5e1;
  --color-text: #1e293b;
  --color-text-muted: #64748b;
  --color-text-light: #94a3b8;

  /* Typography */
  --font-sans: 'Inter', system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', 'Consolas', monospace;

  /* Font Sizes */
  --text-xs: 0.75rem;
  --text-sm: 0.875rem;
  --text-base: 1rem;
  --text-lg: 1.125rem;
  --text-xl: 1.25rem;
  --text-2xl: 1.5rem;
  --text-3xl: 2rem;

  /* Spacing */
  --space-1: 0.25rem;
  --space-2: 0.5rem;
  --space-3: 0.75rem;
  --space-4: 1rem;
  --space-5: 1.25rem;
  --space-6: 1.5rem;
  --space-8: 2rem;
  --space-10: 2.5rem;
  --space-12: 3rem;
  --space-16: 4rem;

  /* Border Radius */
  --radius-sm: 4px;
  --radius-md: 8px;
  --radius-lg: 12px;
  --radius-full: 9999px;

  /* Shadows */
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.07), 0 2px 4px -1px rgba(0, 0, 0, 0.04);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);

  /* Transitions */
  --transition-fast: 150ms ease;
  --transition-base: 200ms ease;
  --transition-slow: 300ms ease;

  /* Container widths */
  --container-max: 1200px;
  --container-narrow: 720px;
}

/* ==========================================================================
   2. Reset & Base Styles
   ========================================================================== */

*,
*::before,
*::after {
  box-sizing: border-box;
}

html {
  font-size: 16px;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

body {
  margin: 0;
  font-family: var(--font-sans);
  font-size: var(--text-base);
  line-height: 1.6;
  color: var(--color-text);
  background-color: var(--color-bg);
}

/* Background utilities */
.bg-page { background-color: var(--color-bg); }
.bg-surface { background-color: var(--color-surface); }

/* ==========================================================================
   3. Typography
   ========================================================================== */

h1, h2, h3, h4, h5, h6 {
  margin: 0 0 var(--space-4);
  font-weight: 600;
  line-height: 1.3;
  color: var(--color-secondary);
}

h1, .text-h1 { font-size: var(--text-3xl); }
h2, .text-h2 { font-size: var(--text-2xl); }
h3, .text-h3 { font-size: var(--text-xl); }
h4, .text-h4 { font-size: var(--text-lg); }

.text-body { font-size: var(--text-base); line-height: 1.6; }
.text-small { font-size: var(--text-sm); line-height: 1.5; }
.text-xs { font-size: var(--text-xs); line-height: 1.4; }
.text-mono { font-family: var(--font-mono); }

.text-muted { color: var(--color-text-muted); }
.text-light { color: var(--color-text-light); }
.text-primary { color: var(--color-primary); }
.text-success { color: var(--color-success); }
.text-error { color: var(--color-error); }

.text-center { text-align: center; }
.text-left { text-align: left; }
.text-right { text-align: right; }

.font-semibold { font-weight: 600; }
.font-normal { font-weight: 400; }

a {
  color: var(--color-primary);
  text-decoration: none;
  transition: color var(--transition-fast);
}

a:hover {
  color: var(--color-primary-hover);
  text-decoration: underline;
}

p {
  margin: 0 0 var(--space-4);
}

/* ==========================================================================
   4. Buttons
   ========================================================================== */

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-2);
  padding: var(--space-3) var(--space-6);
  font-family: var(--font-sans);
  font-size: var(--text-base);
  font-weight: 500;
  line-height: 1.5;
  text-decoration: none;
  border: 1px solid transparent;
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: all var(--transition-base);
}

.btn:hover {
  text-decoration: none;
}

.btn:focus-visible {
  outline: 2px solid var(--color-primary);
  outline-offset: 2px;
}

.btn:disabled {
  opacity: 0.5;
  cursor: not-allowed;
}

/* Primary Button */
.btn-primary {
  background-color: var(--color-primary);
  color: white;
  border-color: var(--color-primary);
}

.btn-primary:hover:not(:disabled) {
  background-color: var(--color-primary-hover);
  border-color: var(--color-primary-hover);
  color: white;
}

/* Secondary Button */
.btn-secondary {
  background-color: var(--color-surface);
  color: var(--color-text);
  border-color: var(--color-border-strong);
}

.btn-secondary:hover:not(:disabled) {
  background-color: var(--color-bg);
  border-color: var(--color-border-strong);
  color: var(--color-text);
}

/* Ghost Button */
.btn-ghost {
  background-color: transparent;
  color: var(--color-text-muted);
  border-color: transparent;
}

.btn-ghost:hover:not(:disabled) {
  background-color: var(--color-bg);
  color: var(--color-text);
}

/* Yandex OAuth Button */
.btn-yandex {
  background-color: var(--color-accent);
  color: white;
  border-color: var(--color-accent);
  width: 100%;
}

.btn-yandex:hover:not(:disabled) {
  background-color: var(--color-accent-hover);
  border-color: var(--color-accent-hover);
  color: white;
}

.btn-yandex svg {
  width: 20px;
  height: 20px;
  flex-shrink: 0;
}

/* Button Sizes */
.btn-sm {
  padding: var(--space-2) var(--space-4);
  font-size: var(--text-sm);
}

.btn-lg {
  padding: var(--space-4) var(--space-8);
  font-size: var(--text-lg);
}

.btn-full {
  width: 100%;
}

/* ==========================================================================
   5. Cards
   ========================================================================== */

.card {
  background-color: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-sm);
  overflow: hidden;
}

.card-header {
  padding: var(--space-4) var(--space-6);
  border-bottom: 1px solid var(--color-border);
  font-weight: 600;
}

.card-body {
  padding: var(--space-6);
}

.card-footer {
  padding: var(--space-4) var(--space-6);
  border-top: 1px solid var(--color-border);
  background-color: var(--color-bg);
}

/* Interactive Card */
.card-interactive {
  display: block;
  text-decoration: none;
  color: inherit;
  transition: all var(--transition-base);
}

.card-interactive:hover {
  text-decoration: none;
  color: inherit;
  box-shadow: var(--shadow-md);
  transform: translateY(-2px);
  border-color: var(--color-border-strong);
}

/* Auth Card (centered modal-like) */
.card-auth {
  max-width: 400px;
  margin: 0 auto;
  padding: var(--space-8) var(--space-6);
}

/* ==========================================================================
   6. Forms
   ========================================================================== */

.form-group {
  margin-bottom: var(--space-5);
}

.form-label {
  display: block;
  margin-bottom: var(--space-2);
  font-size: var(--text-sm);
  font-weight: 500;
  color: var(--color-text);
}

.form-input {
  display: block;
  width: 100%;
  padding: var(--space-3) var(--space-4);
  font-family: var(--font-sans);
  font-size: var(--text-base);
  line-height: 1.5;
  color: var(--color-text);
  background-color: var(--color-surface);
  border: 1px solid var(--color-border-strong);
  border-radius: var(--radius-md);
  transition: border-color var(--transition-fast), box-shadow var(--transition-fast);
}

.form-input::placeholder {
  color: var(--color-text-light);
}

.form-input:focus {
  outline: none;
  border-color: var(--color-primary);
  box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.15);
}

.form-input:disabled {
  background-color: var(--color-bg);
  cursor: not-allowed;
}

/* Error State */
.form-error .form-input {
  border-color: var(--color-error);
}

.form-error .form-input:focus {
  box-shadow: 0 0 0 3px rgba(220, 38, 38, 0.15);
}

.form-hint {
  display: block;
  margin-top: var(--space-2);
  font-size: var(--text-sm);
  color: var(--color-text-muted);
}

.form-error .form-hint {
  color: var(--color-error);
}

/* Checkbox & Radio */
.form-check {
  display: flex;
  align-items: flex-start;
  gap: var(--space-3);
  padding: var(--space-2) 0;
}

.form-check input[type="checkbox"],
.form-check input[type="radio"] {
  width: 18px;
  height: 18px;
  margin: 2px 0 0;
  accent-color: var(--color-primary);
  cursor: pointer;
}

.form-check label {
  font-size: var(--text-base);
  cursor: pointer;
}

/* Submit Button (for forms without .btn class) */
input[type="submit"] {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: var(--space-3) var(--space-6);
  font-family: var(--font-sans);
  font-size: var(--text-base);
  font-weight: 500;
  color: white;
  background-color: var(--color-primary);
  border: 1px solid var(--color-primary);
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: all var(--transition-base);
}

input[type="submit"]:hover {
  background-color: var(--color-primary-hover);
  border-color: var(--color-primary-hover);
}

/* ==========================================================================
   7. Tabs
   ========================================================================== */

.tabs {
  width: 100%;
}

.tabs-list {
  display: flex;
  gap: var(--space-1);
  border-bottom: 2px solid var(--color-border);
  margin-bottom: var(--space-6);
  overflow-x: auto;
}

.tab {
  padding: var(--space-3) var(--space-5);
  font-family: var(--font-sans);
  font-size: var(--text-sm);
  font-weight: 500;
  color: var(--color-text-muted);
  background: transparent;
  border: none;
  border-bottom: 2px solid transparent;
  margin-bottom: -2px;
  cursor: pointer;
  transition: all var(--transition-fast);
  white-space: nowrap;
}

.tab:hover {
  color: var(--color-text);
}

.tab.active {
  color: var(--color-primary);
  border-bottom-color: var(--color-primary);
}

.tab:focus-visible {
  outline: 2px solid var(--color-primary);
  outline-offset: -2px;
}

.tab-panel {
  display: none;
}

.tab-panel.active {
  display: block;
}

/* ==========================================================================
   8. Alerts
   ========================================================================== */

.alert {
  padding: var(--space-4) var(--space-5);
  border-radius: var(--radius-md);
  border: 1px solid;
  font-size: var(--text-sm);
  line-height: 1.5;
}

.alert-success {
  background-color: var(--color-success-bg);
  border-color: var(--color-success-border);
  color: var(--color-success);
}

.alert-error {
  background-color: var(--color-error-bg);
  border-color: var(--color-error-border);
  color: var(--color-error);
}

.alert-warning {
  background-color: var(--color-warning-bg);
  border-color: var(--color-warning-border);
  color: var(--color-warning);
}

.alert-info {
  background-color: var(--color-info-bg);
  border-color: var(--color-info-border);
  color: var(--color-info);
}

/* ==========================================================================
   9. Layout
   ========================================================================== */

.container {
  width: 100%;
  max-width: var(--container-max);
  margin: 0 auto;
  padding: 0 var(--space-4);
}

.container-narrow {
  max-width: var(--container-narrow);
}

/* Flex Utilities */
.flex { display: flex; }
.flex-col { flex-direction: column; }
.flex-wrap { flex-wrap: wrap; }
.items-center { align-items: center; }
.items-start { align-items: flex-start; }
.justify-center { justify-content: center; }
.justify-between { justify-content: space-between; }
.justify-end { justify-content: flex-end; }
.gap-2 { gap: var(--space-2); }
.gap-3 { gap: var(--space-3); }
.gap-4 { gap: var(--space-4); }
.gap-6 { gap: var(--space-6); }
.gap-8 { gap: var(--space-8); }

/* Grid */
.grid {
  display: grid;
  gap: var(--space-6);
}

.grid-cols-1 { grid-template-columns: 1fr; }
.grid-cols-2 { grid-template-columns: repeat(2, 1fr); }
.grid-cols-3 { grid-template-columns: repeat(3, 1fr); }
.grid-cols-4 { grid-template-columns: repeat(4, 1fr); }

/* Auto-fit grid for responsive cards */
.grid-auto {
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
}

/* Centered content */
.center-content {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  min-height: 80vh;
  padding: var(--space-8) var(--space-4);
}

/* ==========================================================================
   10. Spacing Utilities
   ========================================================================== */

.m-0 { margin: 0; }
.mt-2 { margin-top: var(--space-2); }
.mt-4 { margin-top: var(--space-4); }
.mt-6 { margin-top: var(--space-6); }
.mt-8 { margin-top: var(--space-8); }
.mb-2 { margin-bottom: var(--space-2); }
.mb-4 { margin-bottom: var(--space-4); }
.mb-6 { margin-bottom: var(--space-6); }
.mb-8 { margin-bottom: var(--space-8); }
.my-4 { margin-top: var(--space-4); margin-bottom: var(--space-4); }
.my-6 { margin-top: var(--space-6); margin-bottom: var(--space-6); }
.mx-auto { margin-left: auto; margin-right: auto; }

.p-0 { padding: 0; }
.p-4 { padding: var(--space-4); }
.p-6 { padding: var(--space-6); }
.p-8 { padding: var(--space-8); }
.px-4 { padding-left: var(--space-4); padding-right: var(--space-4); }
.py-4 { padding-top: var(--space-4); padding-bottom: var(--space-4); }
.py-6 { padding-top: var(--space-6); padding-bottom: var(--space-6); }
.py-8 { padding-top: var(--space-8); padding-bottom: var(--space-8); }
.py-12 { padding-top: var(--space-12); padding-bottom: var(--space-12); }

/* ==========================================================================
   11. Navigation
   ========================================================================== */

.nav {
  background-color: var(--color-surface);
  border-bottom: 1px solid var(--color-border);
  padding: var(--space-4) 0;
}

.nav-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  max-width: var(--container-max);
  margin: 0 auto;
  padding: 0 var(--space-4);
}

.nav-brand {
  font-size: var(--text-lg);
  font-weight: 600;
  color: var(--color-secondary);
  text-decoration: none;
}

.nav-brand:hover {
  color: var(--color-secondary);
  text-decoration: none;
}

.nav-search-form {
  margin: 0 var(--space-4);
  max-width: 420px;
  width: 100%;
}

.nav-search-form .form-input {
  width: 100%;
}

.nav-links {
  display: flex;
  align-items: center;
  gap: var(--space-6);
  list-style: none;
  margin: 0;
  padding: 0;
}

.nav-link {
  color: var(--color-text-muted);
  font-size: var(--text-sm);
  font-weight: 500;
  text-decoration: none;
  transition: color var(--transition-fast);
}

.nav-link:hover {
  color: var(--color-primary);
  text-decoration: none;
}

.nav-link.active {
  color: var(--color-primary);
}

/* ==========================================================================
   12. Hero Section
   ========================================================================== */

.hero {
  position: relative;
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 400px;
  padding: var(--space-16) var(--space-4);
  text-align: center;
  color: white;
  background-size: cover;
  background-position: center;
}

.hero::before {
  content: '';
  position: absolute;
  inset: 0;
  background: linear-gradient(135deg, rgba(30, 41, 59, 0.85), rgba(37, 99, 235, 0.7));
}

.hero-content {
  position: relative;
  z-index: 1;
  max-width: 700px;
}

.hero-title {
  font-size: clamp(var(--text-2xl), 5vw, var(--text-3xl));
  font-weight: 700;
  margin-bottom: var(--space-4);
  color: white;
  text-shadow: 0 2px 4px rgba(0, 0, 0, 0.2);
}

.hero-subtitle {
  font-size: var(--text-lg);
  opacity: 0.9;
  margin-bottom: var(--space-8);
}

/* ==========================================================================
   13. Video Container
   ========================================================================== */

.video-container {
  position: relative;
  width: 100%;
  padding-top: 56.25%; /* 16:9 aspect ratio */
  background-color: var(--color-secondary);
  border-radius: var(--radius-lg);
  overflow: hidden;
}

.video-container video,
.video-container iframe {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
}

/* ==========================================================================
   14. Quiz Styles
   ========================================================================== */

.quiz-question {
  padding: var(--space-5);
  margin-bottom: var(--space-5);
  background-color: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
}

.quiz-question-text {
  font-weight: 500;
  margin-bottom: var(--space-4);
}

.quiz-options {
  display: flex;
  flex-direction: column;
  gap: var(--space-2);
}

/* Quiz Results */
.quiz-result {
  padding: var(--space-5);
  margin-bottom: var(--space-4);
  border-radius: var(--radius-md);
  border: 1px solid;
}

.quiz-result-correct {
  background-color: var(--color-success-bg);
  border-color: var(--color-success-border);
}

.quiz-result-incorrect {
  background-color: var(--color-error-bg);
  border-color: var(--color-error-border);
}

.quiz-result-label {
  display: inline-block;
  padding: var(--space-1) var(--space-3);
  font-size: var(--text-xs);
  font-weight: 600;
  text-transform: uppercase;
  border-radius: var(--radius-sm);
  margin-bottom: var(--space-3);
}

.quiz-result-correct .quiz-result-label {
  background-color: var(--color-success);
  color: white;
}

.quiz-result-incorrect .quiz-result-label {
  background-color: var(--color-error);
  color: white;
}

/* ==========================================================================
   15. Transcript
   ========================================================================== */

.transcript {
  max-width: var(--container-narrow);
  margin: 0 auto;
}

.transcript-entry {
  margin-bottom: var(--space-4);
}

.transcript-timestamp {
  display: inline-block;
  font-family: var(--font-mono);
  font-size: var(--text-sm);
  color: var(--color-primary);
  cursor: pointer;
  margin-right: var(--space-2);
}

.transcript-timestamp:hover {
  text-decoration: underline;
}

.transcript-speaker {
  font-weight: 600;
  color: var(--color-secondary);
}

/* ==========================================================================
   16. Responsive
   ========================================================================== */

@media (max-width: 768px) {
  :root {
    --text-3xl: 1.75rem;
    --text-2xl: 1.375rem;
  }

  .nav-links {
    gap: var(--space-4);
  }

  .grid-cols-2,
  .grid-cols-3,
  .grid-cols-4 {
    grid-template-columns: 1fr;
  }

  .tabs-list {
    gap: 0;
  }

  .tab {
    padding: var(--space-2) var(--space-3);
    font-size: var(--text-xs);
  }

  .card-auth {
    padding: var(--space-6) var(--space-4);
  }

  .hero {
    min-height: 300px;
    padding: var(--space-10) var(--space-4);
  }
}

@media (min-width: 768px) {
  .md\:grid-cols-2 { grid-template-columns: repeat(2, 1fr); }
  .md\:grid-cols-3 { grid-template-columns: repeat(3, 1fr); }
}

@media (min-width: 1024px) {
  .lg\:grid-cols-3 { grid-template-columns: repeat(3, 1fr); }
  .lg\:grid-cols-4 { grid-template-columns: repeat(4, 1fr); }
}

/* ==========================================================================
   17. Print Styles
   ========================================================================== */

@media print {
  .nav,
  .btn,
  .tabs-list {
    display: none;
  }

  .container {
    max-width: 100%;
    padding: 0;
  }

  .card {
    box-shadow: none;
    border: 1px solid #ccc;
  }
}