/* ==========================================================================
   Core — App shell: header, chat-first layout, sidebars
   ========================================================================== */

/* --- Reset & base --- */
*,
*::before,
*::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html, body {
  height: 100%;
  font-family: var(--font-family-base);
  font-size: var(--font-size-300);
  line-height: var(--line-height-300);
  color: var(--color-neutral-foreground-1);
  background: var(--color-neutral-background-2);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

/* --- App shell layout --- */
.app-shell {
  display: flex;
  flex-direction: column;
  height: 100vh;
  overflow: hidden;
}

/* --- Top bar --- */
.topbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: var(--topbar-height);
  padding: 0 var(--spacing-l);
  background: var(--color-brand-primary);
  color: var(--color-neutral-foreground-on-brand);
  z-index: 100;
  flex-shrink: 0;
}

.topbar-brand {
  display: flex;
  align-items: center;
  gap: var(--spacing-s);
  font-size: var(--font-size-400);
  font-weight: var(--font-weight-semibold);
  text-decoration: none;
  color: inherit;
  cursor: pointer;
}

.topbar-brand img {
  width: 20px;
  height: 20px;
  filter: brightness(0) invert(1);
}

.topbar-actions {
  display: flex;
  align-items: center;
  gap: var(--spacing-m);
}

.topbar-btn {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 36px;
  height: 36px;
  border: none;
  border-radius: var(--radius-medium);
  background: transparent;
  color: var(--color-neutral-foreground-on-brand);
  cursor: pointer;
  transition: background var(--duration-fast) var(--easing-ease);
}

.topbar-btn:hover,
.topbar-btn:focus-visible {
  background: rgba(255, 255, 255, 0.15);
}

.topbar-btn:active {
  background: rgba(255, 255, 255, 0.25);
}

.topbar-btn.active {
  background: rgba(255, 255, 255, 0.2);
}

.topbar-user {
  display: flex;
  align-items: center;
  gap: var(--spacing-s);
  padding: var(--spacing-xs) var(--spacing-s);
  border-radius: var(--radius-medium);
  cursor: pointer;
  border: none;
  background: transparent;
  color: inherit;
  font-size: var(--font-size-200);
}

.topbar-user:hover {
  background: rgba(255, 255, 255, 0.15);
}

.topbar-avatar {
  width: 28px;
  height: 28px;
  border-radius: var(--radius-circular);
  background: rgba(255, 255, 255, 0.3);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: var(--font-size-200);
  font-weight: var(--font-weight-semibold);
}

.topbar-user-name {
  max-width: 140px;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

/* --- Main layout (three-column) --- */
.app-layout {
  display: flex;
  flex: 1;
  overflow: hidden;
}

/* --- Sessions sidebar --- */
.sessions-sidebar {
  width: var(--sessions-sidebar-width);
  background: var(--color-neutral-background-1);
  border-right: 1px solid var(--color-neutral-stroke-2);
  display: flex;
  flex-direction: column;
  flex-shrink: 0;
  overflow: hidden;
  transition: width var(--duration-slow) var(--easing-ease-out),
              opacity var(--duration-normal) var(--easing-ease);
}

.sessions-sidebar.hidden {
  width: 0;
  opacity: 0;
  border-right: none;
  pointer-events: none;
}

.sessions-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: var(--spacing-m) var(--spacing-l);
  font-size: var(--font-size-300);
  font-weight: var(--font-weight-semibold);
  border-bottom: 1px solid var(--color-neutral-stroke-2);
  flex-shrink: 0;
}

.sessions-close-btn {
  width: 28px;
  height: 28px;
  border: none;
  border-radius: var(--radius-medium);
  background: transparent;
  color: var(--color-neutral-foreground-2);
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
}

.sessions-close-btn:hover {
  background: var(--color-neutral-background-3);
}

.sessions-new-btn {
  display: flex;
  align-items: center;
  gap: var(--spacing-s);
  width: 100%;
  padding: var(--spacing-s) var(--spacing-m);
  border: 1px solid var(--color-neutral-stroke-2);
  border-radius: var(--radius-medium);
  background: transparent;
  color: var(--color-brand-primary);
  cursor: pointer;
  font-family: var(--font-family-base);
  font-size: var(--font-size-200);
  font-weight: var(--font-weight-semibold);
}

.sessions-new-btn:hover {
  background: var(--color-neutral-background-3);
}

.sessions-footer {
  padding: var(--spacing-s) var(--spacing-m);
  border-top: 1px solid var(--color-neutral-stroke-2);
  flex-shrink: 0;
}

.sessions-list {
  flex: 1;
  overflow-y: auto;
  padding: var(--spacing-s);
}

.session-item {
  padding: var(--spacing-s) var(--spacing-m);
  border-radius: var(--radius-medium);
  font-size: var(--font-size-200);
  color: var(--color-neutral-foreground-2);
  cursor: pointer;
  transition: background var(--duration-fast);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
  display: flex;
  align-items: center;
  gap: var(--spacing-s);
}

.session-indicator {
  width: 6px;
  height: 6px;
  border-radius: var(--radius-circular);
  background: var(--color-brand-primary);
  flex-shrink: 0;
}

.session-item:hover {
  background: var(--color-neutral-background-3);
}

.session-item.active {
  background: var(--color-brand-light);
  color: var(--color-brand-primary);
  font-weight: var(--font-weight-semibold);
}

/* --- Chat main area --- */
.chat-main {
  flex: 1;
  display: flex;
  flex-direction: column;
  overflow: hidden;
  background: var(--color-neutral-background-2);
  min-width: 0;
}

/* --- File viewer sidebar --- */
.file-viewer {
  width: var(--file-viewer-width);
  background: var(--color-neutral-background-1);
  border-left: 1px solid var(--color-neutral-stroke-2);
  display: flex;
  flex-direction: column;
  flex-shrink: 0;
  overflow: hidden;
  transition: width var(--duration-slow) var(--easing-ease-out),
              opacity var(--duration-normal) var(--easing-ease);
}

.file-viewer.hidden {
  width: 0;
  opacity: 0;
  border-left: none;
  pointer-events: none;
}

/* --- Focus visible --- */
:focus-visible {
  outline: 2px solid var(--color-brand-primary);
  outline-offset: 2px;
}

/* --- Screen reader only --- */
.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;
}

/* --- Hidden utility --- */
.hidden {
  display: none !important;
}

/* Override hidden for sidebar transitions */
.sessions-sidebar.hidden,
.file-viewer.hidden {
  display: flex !important;
}

/* --- Responsive --- */
@media (max-width: 1024px) {
  .file-viewer {
    position: fixed;
    top: var(--topbar-height);
    right: 0;
    bottom: 0;
    z-index: 200;
    box-shadow: var(--shadow-28);
  }
}

@media (max-width: 768px) {
  .sessions-sidebar {
    position: fixed;
    top: var(--topbar-height);
    left: 0;
    bottom: 0;
    z-index: 200;
    box-shadow: var(--shadow-28);
  }

  .sessions-sidebar.hidden {
    display: flex !important;
    transform: translateX(-100%);
    width: var(--sessions-sidebar-width);
    opacity: 1;
  }

  .file-viewer {
    width: 100%;
  }
}