/**
 * Aira Antivirus — Header & Navigation Component
 * Premium Cybersecurity × AI Infrastructure
 * Strictly adhering to:
 * - tokens.css design system
 * - better-accessibility (WCAG 2.1 AA, 44px touch targets, visible focus, ARIA)
 * - better-colors (semantic surface tokens, AA/AAA contrast)
 * - frontend-ui-engineering (mobile-first, zero horizontal overflow, fluid layout)
 */

:root {
  --header-height: 72px;
  --header-height-mobile: 64px;
}

/* ==========================================================================
   1. Header Shell & Sticky / Fixed Positioning
   ========================================================================== */

.site-header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  width: 100%;
  height: var(--header-height);
  z-index: var(--z-header);
  background-color: rgba(7, 9, 13, 0.72);
  backdrop-filter: blur(14px);
  -webkit-backdrop-filter: blur(14px);
  border-bottom: 1px solid var(--border-subtle);
  transition:
    background-color var(--transition-normal),
    border-color var(--transition-normal),
    box-shadow var(--transition-normal),
    height var(--transition-normal);
}

.site-header:focus {
  outline: none;
}

@media (max-width: 767px) {
  .site-header {
    height: var(--header-height-mobile);
  }
}

/* Scrolled State: Increased density, hairline border highlight, ambient shadow */
.site-header--scrolled {
  background-color: rgba(7, 9, 13, 0.92);
  border-bottom-color: var(--border-default);
  box-shadow:
    0 4px 20px rgba(0, 0, 0, 0.5),
    0 1px 0 rgba(255, 255, 255, 0.04);
}

/* Subtle architectural hairline indicator along bottom edge */
.site-header::after {
  content: '';
  position: absolute;
  bottom: -1px;
  left: 10%;
  right: 10%;
  height: 1px;
  background: linear-gradient(
    90deg,
    transparent 0%,
    rgba(59, 102, 255, 0.25) 30%,
    rgba(6, 182, 212, 0.35) 50%,
    rgba(59, 102, 255, 0.25) 70%,
    transparent 100%
  );
  opacity: 0.6;
  pointer-events: none;
  transition: opacity var(--transition-normal);
}

.site-header--scrolled::after {
  opacity: 0.9;
}

/* Header Container */
.header__inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 100%;
  position: relative;
}

/* ==========================================================================
   2. Brand / Logo Aira Antivirus
   ========================================================================== */

.header__brand {
  display: inline-flex;
  align-items: center;
  text-decoration: none;
  color: var(--text-primary);
  border-radius: var(--radius-sm);
  padding: var(--space-1) var(--space-2);
  margin-left: calc(var(--space-2) * -1);
  min-height: var(--hit-target-desktop);
  transition: opacity var(--transition-fast);
}

.header__brand:focus-visible {
  outline: 2px solid var(--color-accent-400);
  outline-offset: 2px;
  box-shadow: var(--focus-ring);
}


/* Unified Official Brandmark Logo */
.header__brand-wrap {
  display: inline-flex;
  flex-direction: column;
  align-items: flex-start;
  gap: 1px;
}

.header__brand-logo {
  height: 32px;
  width: auto;
  max-width: 100%;
  aspect-ratio: 640 / 210;
  display: block;
  object-fit: contain;
  filter: drop-shadow(0 0 10px rgba(59, 102, 255, 0.35));
  transition: filter var(--transition-fast), transform var(--transition-fast);
}

.header__brand-descriptor {
  font-family: var(--font-mono);
  font-size: 0.6rem; /* 9px */
  font-weight: var(--weight-bold);
  letter-spacing: 0.59em;
  margin-right: -0.59em; /* Trims trailing tracking for pixel-exact end-to-end alignment */
  text-transform: uppercase;
  color: var(--color-neutral-400);
  line-height: 1;
  padding-left: 1px;
  transition: color var(--transition-fast);
  display: inline-flex;
  user-select: none;
}

.antivirus-char {
  display: inline-block;
  opacity: 0;
}

/* Variant 1A: Crisp Stagger (100ms) + 3s hold + Soft Dissolve (5.5s cycle) */
.anim-antivirus-a .antivirus-char {
  animation: charFadeInA 5.5s infinite;
  animation-delay: calc(var(--i) * 100ms);
}

@keyframes charFadeInA {
  0% { opacity: 0; transform: translateY(2px); filter: blur(2px); }
  3% { opacity: 1; transform: translateY(0); filter: blur(0); }
  75% { opacity: 1; transform: translateY(0); filter: blur(0); }
  83% { opacity: 0; transform: translateY(0); filter: blur(1.5px); }
  100% { opacity: 0; }
}

@media (prefers-reduced-motion: reduce) {
  .anim-antivirus-a .antivirus-char {
    animation: none;
    opacity: 1;
    transform: none;
    filter: none;
  }
}


@media (max-width: 767px) {
  .header__brand-logo {
    height: 26px;
  }

  .header__brand-descriptor {
    font-size: 0.495rem; /* 7.5px */
    letter-spacing: 0.57em;
    margin-right: -0.57em;
    padding-left: 0.5px;
  }
}

/* ==========================================================================
   3. Desktop Navigation
   ========================================================================== */

.header__nav {
  display: none;
}

@media (min-width: 1024px) {
  .header__nav {
    display: flex;
    align-items: center;
  }
}

.header__nav-list {
  display: flex;
  align-items: center;
  gap: var(--space-1);
  list-style: none;
  margin: 0;
  padding: 0;
}

.header__nav-item {
  position: relative;
}

.header__nav-link {
  display: inline-flex;
  align-items: center;
  padding: var(--space-2) 0.875rem;
  font-family: var(--font-sans);
  font-size: 0.9375rem; /* 15px - optimal readability */
  font-weight: var(--weight-medium);
  color: var(--color-neutral-200);
  text-decoration: none;
  border-radius: var(--radius-md);
  min-height: var(--hit-target-desktop);
  position: relative;
  transition:
    color var(--transition-fast),
    background-color var(--transition-fast);
}

.header__nav-link:hover {
  color: #ffffff;
  background-color: rgba(255, 255, 255, 0.05);
}

.header__nav-link:active {
  color: #ffffff;
  background-color: rgba(255, 255, 255, 0.08);
}

.header__nav-link:focus-visible {
  outline: 2px solid var(--color-accent-400);
  outline-offset: 2px;
  box-shadow: var(--focus-ring);
}

/* Underline indicator for hover / active link */
.header__nav-link::after {
  content: '';
  position: absolute;
  bottom: 4px;
  left: 50%;
  width: 0;
  height: 2px;
  background-color: var(--color-accent-400);
  border-radius: var(--radius-full);
  transform: translateX(-50%);
  transition: width var(--transition-fast), box-shadow var(--transition-fast);
  box-shadow: 0 0 8px rgba(96, 133, 255, 0.6);
}

.header__nav-link:hover::after,
.header__nav-link.is-active::after {
  width: 18px;
}

.header__nav-link.is-active {
  color: var(--text-primary);
  font-weight: var(--weight-semibold);
}

/* ==========================================================================
   4. Header Actions (Language Switcher, CTA, Burger)
   ========================================================================== */

.header__actions {
  display: flex;
  align-items: center;
  gap: var(--space-3);
}

/* Language Switcher Segmented Control with Fluid Elastic Spring Indicator */
.lang-switch {
  position: relative;
  display: inline-flex;
  align-items: center;
  background: #0a0e17;
  border: 1px solid rgba(255, 255, 255, 0.1);
  border-radius: 8px;
  padding: 3px;
  user-select: none;
  box-shadow: var(--shadow-sm);
  box-sizing: border-box;
}

@media (max-width: 479px) {
  .header__actions > .lang-switch {
    display: none;
  }
}

.lang-slide-indicator {
  position: absolute;
  top: 3px;
  bottom: 3px;
  left: 3px;
  width: calc(50% - 3px);
  border-radius: 6px;
  pointer-events: none;
  z-index: 1;
  background: linear-gradient(135deg, #1b263b, #0f172a);
  border: 1px solid rgba(59, 102, 255, 0.5);
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.5);
  transition: transform 320ms cubic-bezier(0.34, 1.45, 0.64, 1);
  box-sizing: border-box;
}

.lang-switch[data-active="ru"] .lang-slide-indicator {
  transform: translateX(100%);
}

.lang-switch__btn {
  position: relative;
  z-index: 2;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  background: transparent;
  border: none;
  text-decoration: none;
  color: var(--text-secondary);
  font-family: var(--font-mono);
  font-size: 11px;
  font-weight: 600;
  letter-spacing: var(--tracking-wider);
  padding: 6px 14px;
  min-height: 28px;
  min-width: 44px;
  cursor: pointer;
  transition: color 0.2s ease;
  text-align: center;
  border-radius: 6px;
  box-sizing: border-box;
  line-height: 1.2;
}

.lang-switch__btn:hover:not(.is-active) {
  color: #ffffff;
}

.lang-switch__btn:focus-visible {
  outline: 2px solid var(--color-accent-400);
  outline-offset: 1px;
}

.lang-switch__btn.is-active {
  color: #ffffff;
}

/* Primary CTA Download Button in Header */
.header__cta {
  display: none;
}

@media (min-width: 640px) {
  .header__cta {
    display: inline-flex;
    min-height: 38px;
    padding: var(--space-2) var(--space-4);
    font-size: var(--text-sm);
  }
}

.header__cta-icon {
  width: 14px;
  height: 14px;
  flex-shrink: 0;
  color: #ffffff;
  opacity: 1;
  transition: transform var(--transition-fast);
}

.header__cta:hover .header__cta-icon {
  transform: none;
  color: #ffffff;
  opacity: 1;
}

/* ==========================================================================
   5. Mobile Hamburger Button
   ========================================================================== */

.header__burger {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 44px;
  height: 44px;
  padding: 0;
  background: transparent;
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  color: var(--text-primary);
  cursor: pointer;
  position: relative;
  transition:
    background-color var(--transition-fast),
    border-color var(--transition-fast);
}

@media (min-width: 1024px) {
  .header__burger {
    display: none;
  }
}

.header__burger:hover {
  background-color: var(--surface-interactive);
  border-color: var(--border-default);
}

.header__burger:focus-visible {
  outline: 2px solid var(--color-accent-400);
  outline-offset: 2px;
  box-shadow: var(--focus-ring);
}

/* Hamburger Icon (CSS Drawn with 3 bars for slick animation) */
.header__burger-box {
  width: 20px;
  height: 14px;
  position: relative;
  display: flex;
  flex-direction: column;
  justify-content: space-between;
}

.header__burger-bar {
  width: 100%;
  height: 2px;
  background-color: currentColor;
  border-radius: var(--radius-full);
  transition:
    transform var(--transition-normal),
    opacity var(--transition-normal);
  transform-origin: center;
}

/* Burger Open State -> Transforms into an 'X' */
.header__burger[aria-expanded="true"] .header__burger-bar:nth-child(1) {
  transform: translateY(6px) rotate(45deg);
}

.header__burger[aria-expanded="true"] .header__burger-bar:nth-child(2) {
  opacity: 0;
  transform: scaleX(0);
}

.header__burger[aria-expanded="true"] .header__burger-bar:nth-child(3) {
  transform: translateY(-6px) rotate(-45deg);
}

/* ==========================================================================
   6. Mobile Menu Overlay & Drawer
   ========================================================================== */

/* Drawer Backdrop */
.header__backdrop {
  position: fixed;
  inset: 0;
  top: var(--header-height);
  background-color: rgba(0, 0, 0, 0.7);
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
  z-index: calc(var(--z-header) - 1);
  opacity: 0;
  visibility: hidden;
  pointer-events: none;
  transition:
    opacity var(--transition-normal),
    visibility var(--transition-normal);
}

@media (max-width: 767px) {
  .header__backdrop {
    top: var(--header-height-mobile);
  }
}

.header__backdrop.is-open {
  opacity: 1;
  visibility: visible;
  pointer-events: auto;
}

/* Mobile Drawer Container */
.header__drawer {
  position: fixed;
  top: var(--header-height);
  left: 0;
  right: 0;
  width: 100%;
  max-height: calc(100dvh - var(--header-height));
  overflow-y: auto;
  overscroll-behavior: contain;
  background-color: rgba(14, 19, 27, 0.98);
  backdrop-filter: blur(20px);
  -webkit-backdrop-filter: blur(20px);
  border-bottom: 1px solid var(--border-strong);
  box-shadow: var(--shadow-elevated);
  z-index: var(--z-header);
  padding: var(--space-6) var(--space-4) var(--space-8);
  display: flex;
  flex-direction: column;
  gap: var(--space-6);
  opacity: 0;
  visibility: hidden;
  transform: translateY(-12px);
  transition:
    opacity var(--transition-normal),
    transform var(--transition-normal),
    visibility var(--transition-normal);
}

@media (max-width: 767px) {
  .header__drawer {
    top: var(--header-height-mobile);
    max-height: calc(100dvh - var(--header-height-mobile));
  }
}

@media (min-width: 1024px) {
  .header__drawer,
  .header__backdrop {
    display: none !important;
  }
}

.header__drawer.is-open {
  opacity: 1;
  visibility: visible;
  transform: translateY(0);
}

/* Mobile Nav List */
.header__mobile-list {
  display: flex;
  flex-direction: column;
  gap: var(--space-1);
  list-style: none;
  margin: 0;
  padding: 0;
}

.header__mobile-link {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: var(--space-3) var(--space-4);
  font-family: var(--font-sans);
  font-size: var(--text-md);
  font-weight: var(--weight-medium);
  color: var(--text-primary);
  text-decoration: none;
  border-radius: var(--radius-md);
  min-height: var(--hit-target-min);
  border: 1px solid transparent;
  transition:
    background-color var(--transition-fast),
    border-color var(--transition-fast),
    color var(--transition-fast);
}

.header__mobile-link:hover {
  background-color: var(--surface-interactive);
  border-color: var(--border-subtle);
}

.header__mobile-link.is-active {
  background-color: var(--surface-interactive);
  border-color: var(--border-accent);
  color: #38bdf8;
  font-weight: var(--weight-semibold);
}

.header__mobile-link.is-active .header__mobile-link-chevron {
  color: var(--color-cyan-400);
}

.header__mobile-link:focus-visible {
  outline: 2px solid var(--color-accent-400);
  outline-offset: 2px;
  box-shadow: var(--focus-ring);
}

.header__mobile-link-chevron {
  width: 16px;
  height: 16px;
  color: var(--text-tertiary);
  transition: transform var(--transition-fast), color var(--transition-fast);
}

.header__mobile-link:hover .header__mobile-link-chevron {
  color: var(--color-cyan-400);
  transform: translateX(3px);
}

/* Mobile Drawer Bottom Section */
.header__mobile-footer {
  display: flex;
  flex-direction: column;
  gap: var(--space-4);
  padding-top: var(--space-4);
  border-top: 1px solid var(--border-subtle);
}

.header__mobile-cta {
  width: 100%;
  min-height: 48px;
  font-size: var(--text-base);
}

.header__mobile-meta {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-3);
  padding-top: var(--space-2);
}

/* Prevent body scrolling when mobile drawer is open */
body.mobile-menu-active {
  overflow: hidden !important;
}

/* ==========================================================================
   7. Reduced Motion Fallback
   ========================================================================== */

@media (prefers-reduced-motion: reduce) {
  .site-header,
  .site-header::after,
  .header__burger-bar,
  .header__drawer,
  .header__backdrop,
  .header__nav-link,
  .header__nav-link::after,
  .header__logo-img {
    transition: opacity 0.01ms !important;
    transform: none !important;
  }

  .header__drawer {
    transform: none !important;
  }
}