hyperhive/frontend/packages/swarm-ui/src/shell/Shell.tsx

// <Shell> — page chrome every swarm-ui route mounts inside: a header
// bar (swarm branding) plus a nav row linking the app's real routes.
// Preact-native styling — `./Shell.css` imported right here, not
// wired centrally, so the component and its styles travel together
// (esbuild folds every imported `.css` reachable from `main.tsx` into
// one `main.css` companion output, see build.mjs) — deliberately not
// @hive/shared's chrome.css page-header pattern, which is the per-hive
// MPA dashboard's visual language. This package is a clean field, not
// an inheritor of that look.
//
// Route list lives here, not prop-drilled from App — one small SPA
// has exactly one place that needs to know its own nav, and this is
// it. Grows additively as real routes land (a swarm-wide agent roster
// is next); no speculative entries.
//
// Page-switch animation, two pieces (motion-guard rules live in
// Shell.css): `.shell-body` remounts on every navigation
// (`key={location}`) to replay a plain fade-in, and a single shared
// underline (`.shell-nav-indicator`, replacing what used to be a
// per-link border) hops through every nav item it passes over on its
// way to the new active one, not just a straight two-point tween — a
// nav hives→components jump visibly touches "new agent" and "jobs" in
// between, position and colour together. Accent is a discrete cycle
// through the existing base16 chromatic slots (`NAV_ITEMS`' `accent`
// field), not a continuous hue rotation — everything here still
// derives from base16, same rule the rest of the palette follows.
import { useEffect, useRef, useState } from 'preact/hooks';
import type { ComponentChildren } from 'preact';
import { Link, useLocation } from 'wouter-preact';
import { LinksMenu } from './LinksMenu.js';
import { SettingsMenu } from './SettingsMenu.js';
import { useApplyThemeOverride } from '../lib/theme-apply.js';
import { useApplyMotionOverride } from '../lib/motion-apply.js';
import './Shell.css';

const NAV_ITEMS: { href: string; label: string; accent: string }[] = [
  { href: '/', label: 'hives', accent: 'var(--purple)' },
  { href: '/create-agent', label: 'new agent', accent: 'var(--cyan)' },
  { href: '/jobs', label: 'jobs', accent: 'var(--pink)' },
  { href: '/components', label: 'components', accent: 'var(--blue)' },
];

// Static fallback — matches `index.html`'s `<title>` default, so a page
// never flashes something else before the fetch below resolves, and an
// operator who never set `services.hyperhive.swarm.name` sees the exact
// same generic label the pre-fetch page already showed, not a blank.
const DEFAULT_BRAND = 'hyperhive swarm';

interface IndicatorRect {
  left: number;
  top: number;
  width: number;
  accent: string;
}

// One hop's travel time — also the interval between hops, so each leg
// finishes (per `.shell-nav-indicator`'s own CSS transition duration,
// kept equal to this) before the next one starts rather than the two
// blending into a single averaged easing curve.
const HOP_MS = 140;

// `data-motion`/`prefers-reduced-motion` gate for the JS-driven hop
// sequence — the CSS-only pieces (the fade, the indicator's own
// transition) gate via the three-rule pattern in Shell.css, but a
// multi-step `setTimeout` sequence has no CSS equivalent to hook, so it
// checks the same two sources directly. `data-motion` takes precedence
// over the OS preference either direction (reduce *or* allow), same
// override semantics `lib/motion-apply.ts` establishes.
function prefersReducedMotion(): boolean {
  const override = document.documentElement.dataset.motion;
  if (override === 'reduce') return true;
  if (override === 'allow') return false;
  return window.matchMedia('(prefers-reduced-motion: reduce)').matches;
}

function NavLink({
  href,
  label,
  active,
  textRef,
}: {
  href: string;
  label: string;
  active: boolean;
  textRef: (el: HTMLSpanElement | null) => void;
}) {
  return (
    <Link href={href} className="shell-nav-link">
      {/* Touch target (min-height) lives on the <a> so the whole row is
          tappable. The underline itself no longer lives here — see
          `.shell-nav-indicator` — this span is still what gets
          measured to position that shared indicator, so it hugs just
          the text rather than the full-height tappable box. */}
      <span
        ref={textRef}
        class={'shell-nav-link-text' + (active ? ' shell-nav-link-active' : '')}
      >
        {label}
      </span>
    </Link>
  );
}

export function Shell({ children }: { children: ComponentChildren }) {
  const [swarmName, setSwarmName] = useState<string | null>(null);
  const [location] = useLocation();
  const navRef = useRef<HTMLElement | null>(null);
  const textRefs = useRef<Record<string, HTMLSpanElement | null>>({});
  const [indicator, setIndicator] = useState<IndicatorRect | null>(null);
  // The nav-item index the indicator is currently sitting at (or mid-hop
  // from) — distinct from `location`'s own index, since the two only
  // agree once every intermediate hop has landed. `-1` = not settled
  // anywhere yet (first mount) or on a route with no nav item (404).
  const settledIndexRef = useRef(-1);

  // Applied once here, not inside `SettingsMenu` — every route mounts
  // through this one `<Shell>`, so the override takes effect regardless
  // of which page is showing or whether the menu's ever been opened,
  // and `useLocalSetting`'s same-tab subscription (settings-storage.ts)
  // means `SettingsMenu` changing the stored value re-runs these
  // effects without either component needing a reference to the other.
  useApplyThemeOverride();
  useApplyMotionOverride();

  // Measures nav item `index`'s rect relative to `.shell-nav`.
  // `getBoundingClientRect()` on both elements at the same tick keeps
  // this scroll-position-agnostic — a difference of two
  // viewport-relative rects is scroll-invariant, no separate
  // scroll-offset bookkeeping needed.
  function measureIndex(index: number): IndicatorRect | null {
    const navEl = navRef.current;
    const item = NAV_ITEMS[index];
    const textEl = item ? textRefs.current[item.href] : null;
    if (!navEl || !item || !textEl) return null;
    const navRect = navEl.getBoundingClientRect();
    const textRect = textEl.getBoundingClientRect();
    return {
      left: textRect.left - navRect.left,
      top: textRect.bottom - navRect.top,
      width: textRect.width,
      accent: item.accent,
    };
  }

  // Drives the indicator through every nav item between where it was
  // and the new active one — see the file-top comment for why (mara:
  // "navigating from a to c animates [a's colour] -> [b's colour] ->
  // [c's colour]"). Re-runs on navigation; a separate resize listener
  // below re-measures the already-settled position without re-hopping
  // (a reflow isn't a navigation).
  useEffect(() => {
    const targetIndex = NAV_ITEMS.findIndex((item) => item.href === location);
    if (targetIndex === -1) {
      settledIndexRef.current = -1;
      setIndicator(null);
      return;
    }
    const fromIndex = settledIndexRef.current;
    // First mount, a route with no nav item just left, or reduced
    // motion: land directly, no intermediate hops to sweep through.
    if (fromIndex === -1 || prefersReducedMotion()) {
      settledIndexRef.current = targetIndex;
      setIndicator(measureIndex(targetIndex));
      return;
    }
    const step = targetIndex > fromIndex ? 1 : -1;
    let cancelled = false;
    let timeoutId: number | undefined;
    function hop(current: number) {
      const next = current + step;
      setIndicator(measureIndex(next));
      settledIndexRef.current = next;
      if (next !== targetIndex) {
        timeoutId = window.setTimeout(() => {
          if (!cancelled) hop(next);
        }, HOP_MS);
      }
    }
    hop(fromIndex);
    return () => {
      cancelled = true;
      if (timeoutId !== undefined) window.clearTimeout(timeoutId);
    };
  }, [location]);

  // Re-measures the current (already-settled) position on resize — the
  // nav's own `flex-wrap` means a link's position genuinely changes at
  // narrow widths, not just its route. Not part of the hop effect above
  // since a reflow shouldn't restart the sweep animation.
  useEffect(() => {
    function onResize() {
      if (settledIndexRef.current === -1) return;
      setIndicator(measureIndex(settledIndexRef.current));
    }
    window.addEventListener('resize', onResize);
    return () => window.removeEventListener('resize', onResize);
  }, []);

  // Fetched once here, not per-page: every route mounts inside one
  // `<Shell>`, and the swarm's name doesn't change within a page
  // visit. A fetch failure is silently ignored — `swarmName` just stays
  // `null` and the header/title fall back to `DEFAULT_BRAND`, same as
  // an operator who never configured a name; this label is cosmetic,
  // not worth an `ApiErrorPanel`.
  useEffect(() => {
    (async () => {
      const r = await fetch('/api/swarm');
      if (!r.ok) return;
      const data = (await r.json()) as { name: string | null };
      if (data.name) setSwarmName(data.name);
    })().catch(() => {
      /* cosmetic only — see comment above */
    });
  }, []);

  const brand = swarmName ?? DEFAULT_BRAND;
  useEffect(() => {
    document.title = brand;
  }, [brand]);

  return (
    <div class="shell">
      <header class="shell-header">
        <span class="shell-brand">{brand}</span>
        <nav class="shell-nav" ref={navRef}>
          {NAV_ITEMS.map((item) => (
            <NavLink
              key={item.href}
              href={item.href}
              label={item.label}
              active={item.href === location}
              textRef={(el) => {
                textRefs.current[item.href] = el;
              }}
            />
          ))}
          {/* Shared sliding underline — see the file-top comment. Hidden
              (zero width) rather than unmounted when there's no active
              nav item (404), so it doesn't pop in with a stale position
              the next time a real nav item becomes active. */}
          <span
            class="shell-nav-indicator"
            style={{
              left: `${indicator?.left ?? 0}px`,
              top: `${indicator?.top ?? 0}px`,
              width: `${indicator?.width ?? 0}px`,
              backgroundColor: indicator?.accent ?? 'transparent',
            }}
          />
        </nav>
        {/* Single `margin-left: auto` on the wrapper, not on each menu
            individually — two adjacent flex items both set to
            `margin-left: auto` split the available space between them
            instead of sitting flush together at the right edge. */}
        <div class="shell-header-actions">
          <SettingsMenu />
          <LinksMenu />
        </div>
      </header>
      {/* Keyed by route so it remounts (and replays its entrance
          animation) on every navigation — see the file-top comment. */}
      <div class="shell-body" key={location}>
        {children}
      </div>
    </div>
  );
}