hanzo.ai/app/(app)/chat/_door.tsx

'use client'

// /chat, and by the edge every conversation under it (lib/edge.ts `APP`): the
// app in Chat. A conversation is its path, `/chat/<id>` (@hanzo/app lib/host
// `talk`, `place`).
//
//   signed in    the app (app/_web.tsx), drawn here as on `/`. A conversation
//                at the address it had before, `/chat?thread=<id>`, is moved to
//                its path first, once, so Back does not land on it (`moved`).
//   signed out   sign in first (destination.ts `enter`). The address is written
//                down on the way out, so the sign-in returns here and the first
//                case takes over.

import { useEffect, useState } from 'react'
import dynamic from 'next/dynamic'
import { useIam } from '@hanzo/iam/react'
import { enter } from '@hanzo/app/lib/destination'
import { CHAT, talk } from '@hanzo/app/lib/host'

/** The app, fetched only for a signed-in reader. */
const App = dynamic(() => import('../../_web'), { ssr: false })

/** The path a retired Chat address names; null when it is current. */
export function moved(pathname: string, q: URLSearchParams): string | null {
  if (pathname !== CHAT) return null
  const thread = q.get('thread')
  return thread ? talk(thread) : null
}

export function Door() {
  const { isLoading, isAuthenticated } = useIam()
  const [ready, setReady] = useState(false)

  useEffect(() => {
    if (isLoading) return
    if (!isAuthenticated) return enter()
    const to = moved(window.location.pathname, new URLSearchParams(window.location.search))
    if (to) window.history.replaceState(null, '', to)
    setReady(true)
  }, [isLoading, isAuthenticated])

  return ready ? <App /> : null
}