packages/app/src/pages/session/session-lineage.ts

import { createEffect, createMemo, createSignal, on, onCleanup } from "solid-js"
import { sessionNotFoundError } from "@/utils/server-errors"

type LineageStore<T> = { peek: (id: string) => T | undefined; resolve: (id: string) => Promise<unknown> }

type Resolution<T> = { id: string; store: LineageStore<T> } & (
  | { state: "pending" }
  | { state: "settled" }
  | { state: "failed"; failure: unknown }
)

// Reactive session lineage for the target session route, read from the sync store.
// All session tabs on a server share one route instance, so the target session ID
// changes in place; the effect is only a trigger that starts resolution for the
// current target, and each run cancels the previous one through onCleanup so a
// late result from an abandoned target is dropped. Resolution is imperative rather
// than a resource on purpose: a resource created here would be created inside the
// router's navigation transition, and suspending that transition deadlocks the URL
// commit and double-mounts the session header portals from the transition's shadow
// render.
//
// The returned accessor is a pure derivation. The sync cache is authoritative, and
// status only applies while it matches the current target (store + session ID): on
// navigation or store replacement the memo re-evaluates before the trigger runs,
// so trusting a previous target's settlement would fabricate a not-found for a
// session that simply has not resolved yet. Resolve failures rethrow on read so
// the enclosing SessionRouteErrorBoundary renders the scoped session error.
export function createSessionLineage<T>(sessionID: () => string, lineage: () => LineageStore<T>) {
  const cached = createMemo(() => lineage().peek(sessionID()))
  const [status, setStatus] = createSignal<Resolution<T>>()

  createEffect(
    on([sessionID, lineage] as const, ([id, store]) => {
      let stale = false
      onCleanup(() => {
        stale = true
      })
      if (cached()) {
        setStatus({ id, store, state: "settled" })
        return
      }
      setStatus({ id, store, state: "pending" })
      store
        .resolve(id)
        .then(() => {
          if (!stale) setStatus({ id, store, state: "settled" })
        })
        .catch((failure) => {
          if (!stale) setStatus({ id, store, state: "failed", failure })
        })
    }),
  )

  return createMemo(() => {
    const id = sessionID()
    const value = cached()
    if (value) return value
    const state = status()
    if (state?.id !== id || state.store !== lineage()) return undefined
    if (state.state === "failed") throw state.failure
    // The viewed session is pinned (DirectoryDataProvider, directory-layout.tsx)
    // and pinned lineages are exempt from cache pruning, so a lineage missing
    // after settlement means the session (or an ancestor) was deleted, possibly
    // by another client. Match the resolve error so the boundary shows the
    // session not found fallback.
    if (state.state === "settled") throw sessionNotFoundError(id)
    return undefined
  })
}