/**
 * Real-UI assembly closure. Runs only after loader.settled(): the whole
 * layout tree hangs off the built-in 'root' slot (ui-layout registers
 * AppFrame there and renders the child slots internally) — the shell's
 * render is the one ctx-level renderSlot call in the program.
 */
import type { ReactNode } from 'react'
import type { Context } from 'cordis'
import type { SessionsService } from '@deepseek-ai/dsh-client-runtime/client'
import { bindSnapshotSelector } from '@deepseek-ai/dsh-client-web-react'
import { DocumentTitle } from './DocumentTitle.tsx'
// Type-only: pulls the runtime's SlotMap declaration merge (the 'root' key) into this program.
import type {} from '@deepseek-ai/dsh-client-runtime/client'

/** Assembly inputs: the settled root ctx plus the loader's module-table read surface. */
export interface AssemblyDeps {
  /** Client root context (all plugin services provided). */
  ctx: Context
  /** Module-table resolver (the loader's require; missing spec = throw). Kept in the seam for future shell needs. */
  requireModule: (spec: string) => unknown
}

/**
 * Build the renderApp factory handed to AppRoot.
 * @param deps - assembly inputs.
 * @returns factory producing the real UI tree (called once per AppRoot render after settled).
 */
export function buildRenderApp(deps: AssemblyDeps): () => ReactNode {
  const { ctx } = deps
  const sessions = ctx.get('sessions') as SessionsService | undefined
  if (sessions === undefined) throw new Error('shell assembly: sessions service unavailable')
  const useSessions = bindSnapshotSelector(sessions.list)
  const SessionDocumentTitle = (): ReactNode => {
    const title = useSessions((state) => {
      const id = state.current
      return id === undefined ? undefined : state.byId[id]?.title
    })
    return <DocumentTitle {...title === undefined ? {} : { title }} />
  }
  return () => (
    <>
      <SessionDocumentTitle />
      {ctx.slots.renderSlot('root', {})}
    </>
  )
}