/* -- Session component -------------------------------------------
   A chat session: a scrolling transcript (role="log") that follows the
   live edge, jumps back to it, keeps its place when history loads, anchors
   new turns, and takes dropped files - plus a footer for the composer.
   The runtime keeps the data-* state current; CSS draws from it. */

@layer components {
  .session {
    position: relative;
    display: flex;
    flex-direction: column;
    min-height: 0;
    overflow: hidden;
    border: 1px solid var(--border);
    border-radius: var(--radius-xl);
    background: var(--card);
    color: var(--card-foreground);
  }

  /* -- Viewport: the scroller --------------------------------------- */
  .session-viewport {
    position: relative;
    display: flex;
    flex-direction: column;
    flex: 1;
    min-height: 0;
    padding: 1rem;
    overflow-y: auto;
    overscroll-behavior: contain;
    /* the runtime keeps the reader's place when history prepends - the
       browser's own scroll anchoring would correct twice */
    overflow-anchor: none;
    scrollbar-gutter: stable;

    &:focus-visible {
      outline: 2px solid var(--ring);
      outline-offset: -2px;
    }
  }

  /* short threads sit at the bottom, like every chat */
  .session-content {
    display: flex;
    flex-direction: column;
    gap: 1rem;
    margin-block-start: auto;
  }

  /* rows off screen skip rendering; their size is remembered. content-
     visibility implies paint containment, which clips at the row's edge -
     the clip margin lets bubble tails, reactions and focus rings draw
     outside it */
  .session-item {
    content-visibility: auto;
    contain-intrinsic-size: auto 3.5rem;
    overflow-clip-margin: 1rem;

    &[data-current] { scroll-margin-block-start: 1rem; }
  }

  /* data-animate: new rows rise in */
  .session[data-animate] .session-item {
    transition: opacity 250ms ease, translate 250ms ease;

    @starting-style {
      opacity: 0;
      translate: 0 0.5rem;
    }
  }

  /* -- Scroll buttons: float over the transcript, stuck to its edge -- */
  .session-scroll-button {
    position: sticky;
    z-index: 1;
    align-self: center;
    flex: none;
    display: grid;
    place-items: center;
    width: 2.25rem;
    height: 2.25rem;
    margin: 0;
    padding: 0;
    border: 1px solid var(--border);
    border-radius: 999px;
    background: var(--background);
    color: var(--foreground);
    box-shadow: var(--shadow-md);
    cursor: pointer;
    opacity: 0;
    scale: 0.85;
    visibility: hidden;
    transition: opacity 150ms, scale 150ms, visibility 150ms allow-discrete, background-color 150ms;

    /* a chevron, drawn */
    &::before {
      content: "";
      width: 0.5rem;
      height: 0.5rem;
      border-inline-end: 2px solid currentColor;
      border-block-end: 2px solid currentColor;
      rotate: 45deg;
      translate: 0 -0.125rem;
    }

    &:hover { background: var(--accent); color: var(--accent-foreground); }
    &:focus-visible { outline: 2px solid var(--ring); outline-offset: 2px; }

    /* to the end: at the bottom edge, overlaying the last row */
    &[data-to="end"] {
      order: 2;
      inset-block-end: 0.5rem;
      margin-block-start: -2.25rem;
    }
    /* to the start: at the top edge, pointing up */
    &[data-to="start"] {
      order: -1;
      inset-block-start: 0.5rem;
      margin-block-end: -2.25rem;
      &::before { rotate: -135deg; translate: 0 0.125rem; }
    }
  }

  .session[data-scrollable~="end"] .session-scroll-button[data-to="end"],
  .session[data-scrollable~="start"] .session-scroll-button[data-to="start"] {
    opacity: 1;
    scale: 1;
    visibility: visible;
  }

  /* -- Footer: the composer, a status line ---------------------------- */
  .session-footer {
    flex: none;
    padding: 0.75rem;
    border-top: 1px solid var(--border);
    background: var(--card);
  }

  .session-status {
    padding: 0.375rem 1rem;
    border-top: 1px solid var(--border);
    color: var(--muted-foreground);
    font-size: 0.75rem;
  }

  /* -- Drop target: files dragged over the session ----------------------- */
  .session[data-drop-active]::after {
    content: attr(data-drop-label);
    position: absolute;
    inset: 0.5rem;
    z-index: 2;
    display: grid;
    place-items: center;
    border: 2px dashed var(--ring);
    border-radius: var(--radius-lg);
    background: color-mix(in oklch, var(--background) 85%, transparent);
    color: var(--foreground);
    font-size: 0.875rem;
    font-weight: 500;
    pointer-events: none;
  }

  /* -- Accessibility -------------------------------------------- */
  @media (prefers-reduced-motion: reduce) {
    .session-scroll-button,
    .session[data-animate] .session-item { transition: none; }
  }

  @media (prefers-contrast: more) {
    .session,
    .session-footer,
    .session-scroll-button { border-color: var(--foreground); }
  }

  @media (forced-colors: active) {
    .session { border: 1px solid CanvasText; }
    .session-scroll-button { border: 1px solid ButtonText; }
    .session[data-drop-active]::after { border-color: Highlight; forced-color-adjust: none; }
  }
}