// ---------------------------------------------------------------------------
// customer-grid / liveWorkspace.ts
// The workspace that arrives AFTER mount — pure and React-free, so
// verify_live_workspace.py can run it under node.
//
// ⛔ THE DEFECT THIS EXISTS FOR (owner, 2026-08-04). "Creating a new Cohort or
// Locked list under Product/Customer only shows up when I click a different
// module first and come back."
//
// It was exact. `CustomerGrid`'s init effect is gated on
// `initializedKey.current === storageKey`, so it reads `payload.workspace`
// EXACTLY ONCE per mount. Under Streamlit that was invisible — a rerun replaces
// the iframe, so every host round trip WAS a remount and init ran again. The
// standalone shell has no rerun: `CustomerGrid` stays mounted, and the only
// thing that remounts it is `key={active.key}` in Shell.tsx — i.e. switching
// modules, which is precisely the workaround the owner found.
//
// So the write path was complete and the READ path stopped at the door:
// `add_to_list` → the host creates the set → `rerender: true` →
// WORKSPACE_STALE_EVENT → `reread()` → `payload.workspace` genuinely carries the
// new locked view (wave 17 R1 projects every cohort as a view) — and `views`
// state, seeded once at init, never heard about it.
//
// TWO STRATA GO STALE TOGETHER, and fixing only the first would have looked
// fixed while staying broken:
//   views   the projected locked view = the rail row the owner is looking for.
//   fields  `fields_from_workspace(ws, cohorts=bool(cohort_lists))` — the
//           derived "Locked views" column EXISTS ONLY ONCE A COHORT DOES. The
//           user's FIRST cohort therefore changes the field contract, and an
//           init-once `fields` would have left that column out of the Fields
//           menu until the very remount we are removing the need for.
//
// ⭐ ADD-ONLY, AND THAT IS A DESIGN DECISION, NOT AN OMISSION. Everything the
// user already holds is left BY IDENTITY: an in-flight filter tree, a config
// mid-autosave (420 ms debounce), a rename waiting on its echo. This module is
// the answer to "what has APPEARED since we mounted", and nothing else. Taking
// host copies of things we already hold would re-introduce every blip
// optimism.ts / viewEcho.ts / folders.ts were written to remove — the whole
// no-blip layer rests on "this browser's copy is the newest truth".
//
// ⚠ TOMBSTONES ARE NOT OPTIONAL HERE, and an add-only merge without them is
// WORSE than the bug it fixes. The event queue sends ONE batch at a time
// (apiBridge `drain`), so this interleaving is ordinary:
//     batch 1 [add_to_list]  in flight
//     user deletes a view    → removed optimistically, queued behind batch 1
//     batch 1 answers        → rerender → reread → the workspace STILL lists
//                              the deleted view (its delete has not been sent)
// Without a tombstone the row comes back — and since this merge never removes,
// it would stay back until a remount. That is a delete that visibly failed.
// Same window and same rule as folders.ts and optimism.ts: ECHO_RECENT_MS, and
// anything past it yields to the host, because divergence is not an echo.
// ---------------------------------------------------------------------------

import { ECHO_RECENT_MS } from "./viewEcho";
import type { Field, SavedView, ViewConfig } from "./types";

/** id -> when THIS browser deleted it. Browser-clock arithmetic on purpose:
 *  both sides of the comparison come from this machine, so this is not the
 *  tenant-day contract ([[date-window-vocabulary]]) — that one is about two
 *  ENGINES agreeing on a date. */
export type Tombstones = Record<string, number>;

/** Upper bound on a tombstone map, matching FOLDER_STAMP_MAX. A long-lived tab
 *  must not accumulate an archive of everything it ever deleted. */
export const TOMBSTONE_MAX = 64;

const isRecent = (t: number | undefined, now: number): boolean =>
  typeof t === "number" && now - t <= ECHO_RECENT_MS;

/** Drop entries past the echo window. Called at every stamp AND before every
 *  persist, so the blob stays a recent window rather than a growing log. */
export function pruneTombstones(stamps: Tombstones | undefined, now: number): Tombstones {
  const kept = Object.entries(stamps ?? {}).filter(
    ([, t]) => typeof t === "number" && isRecent(t, now)
  );
  return Object.fromEntries(kept.slice(-TOMBSTONE_MAX));
}

/** Record one deletion. Pure so the caller's ref update stays a one-liner. */
export function stampTombstone(stamps: Tombstones | undefined, id: string, now: number): Tombstones {
  return pruneTombstones({ ...(stamps ?? {}), [id]: now }, now);
}

/**
 * ⭐ D-19 (wave 20) — **THE LOCALSTORAGE GHOST.**
 *
 * At init the grid seeded EVERY view from localStorage and then merged the host's list over the
 * top, so a view the host no longer names simply survived — for ever, in that browser. Three
 * ordinary paths produce one: the view was deleted from another tab or another machine, its
 * share was revoked, or the store moved under it. The row keeps working until you click it, and
 * then it is a saved view nobody else can see and no write can reach; the owner reported it as
 * "live and staging disagree". Item 13's pg cutover makes the host list authoritative for real,
 * which turns a rare confusion into a visible one.
 *
 * So: **the host's list decides which views exist.** A local copy the host does not name is
 * dropped — with two guards, and neither is optional:
 *
 *   1. `hostAuthoritative === false` keeps everything. Standalone with no `/workspace` (and the
 *      legacy embed) has no host list at all, and "not named" there means "not asked", not
 *      "deleted". Dropping on a payload that never carried views would empty the rail.
 *      ⛔ **An EMPTY host list counts as not-authoritative for the same reason, and this is the
 *      one branch that could destroy data.** A `/workspace` answering `200 {views: []}` is
 *      indistinguishable from a store that has not answered yet — a scope whose bucket is
 *      briefly empty during item 13's `hf → pg` migration, a fresh backend, a bucket that was
 *      never seeded. Dropping there wipes every saved view in that browser, and the persist
 *      effect rewrites localStorage immediately after, so there is no second chance. The ghost
 *      this exists for is a view missing from a NON-EMPTY list; nothing is lost by refusing to
 *      act on no list at all.
 *   2. A view THIS BROWSER wrote inside the echo window survives. A create is optimistic: the
 *      row exists locally the instant it is made, and the host cannot name it until its
 *      `view_upsert` has been sent AND the next `/workspace` read has come back. Without this
 *      guard, creating a view and reloading fast enough would delete it — the exact inverse of
 *      the bug, and a worse one.
 *
 * Same window, same reasoning and the same stamp shape as the tombstones above: past
 * ECHO_RECENT_MS, divergence is not an echo.
 */
export function seedLocalViews(
  localViews: readonly SavedView[],
  hostViews: readonly SavedView[],
  writes: Tombstones | undefined,
  now: number,
  hostAuthoritative: boolean
): SavedView[] {
  if (!hostAuthoritative || hostViews.length === 0) return [...localViews];
  const named = new Set(hostViews.map((v) => v.id));
  return localViews.filter((v) => named.has(v.id) || isRecent(writes?.[v.id], now));
}

/**
 * Views that have APPEARED on the host since this browser last looked.
 *
 * Returns `current` BY IDENTITY when there is nothing to adopt — which is the
 * load-bearing half of the contract, not an optimisation. `withWorkspace` mints
 * a fresh payload object on every re-read, so `hostViews` changes identity each
 * time whether or not its contents did; a merge that always returned a new
 * array would re-render the grid (and re-write localStorage) on every echo.
 *
 * `normalize` is injected rather than imported because it needs the FIELD LIST
 * the caller is about to commit — a locked view's projected `config.order` names
 * the derived cohort column, and normalizing against a stale field array would
 * quietly drop the very key that arrived with it. The caller therefore adopts
 * fields FIRST and hands the result down (see CustomerGrid's live effect).
 */
export function adoptNewViews(
  current: SavedView[],
  hostViews: SavedView[] | undefined,
  tombstones: Tombstones | undefined,
  now: number,
  normalize: (config: Partial<ViewConfig> | undefined) => ViewConfig
): SavedView[] {
  if (!Array.isArray(hostViews) || hostViews.length === 0) return current;
  const held = new Set(current.map((v) => v.id));
  const fresh: SavedView[] = [];
  for (const view of hostViews) {
    if (!view || typeof view.id !== "string" || view.id === "") continue;
    if (held.has(view.id)) continue;
    // Deleted here seconds ago and the echo has not caught up. Resurrecting it —
    // even for one round trip — is the delete blip, and this merge never removes,
    // so it would be a permanent one.
    if (isRecent(tombstones?.[view.id], now)) continue;
    held.add(view.id);                    // a host list with a duplicate id adds once
    fresh.push({ ...view, config: normalize(view.config) });
  }
  return fresh.length === 0 ? current : [...current, ...fresh];
}

/**
 * Fields that have APPEARED on the host since this browser last looked — in
 * practice the derived "Locked views" column, which the server emits only once
 * the user owns at least one cohort.
 *
 * Appended in host order at the END, which is where `fields_from_workspace`
 * puts the derived column anyway, and `reconcileOrder` folds any key missing
 * from a saved `config.order` in for us — so nothing has to touch a stored view
 * for the new column to become togglable in the Fields menu.
 *
 * ⚠ The tombstone map here is `FieldStamps.deleted`, the SAME one
 * `reconcileFields` consults at mount, for the same reason: a column this
 * browser dropped must not walk back in through a lagged echo.
 */
export function adoptNewFields(
  current: Field[],
  hostFields: Field[] | undefined,
  tombstones: Tombstones | undefined,
  now: number
): Field[] {
  if (!Array.isArray(hostFields) || hostFields.length === 0) return current;
  const held = new Set(current.map((f) => f.key));
  const fresh: Field[] = [];
  for (const field of hostFields) {
    if (!field || typeof field.key !== "string" || field.key === "") continue;
    if (held.has(field.key)) continue;
    if (isRecent(tombstones?.[field.key], now)) continue;
    held.add(field.key);
    fresh.push(field);
  }
  return fresh.length === 0 ? current : [...current, ...fresh];
}

// ===========================================================================
// THE CHANGE TOKEN (wave 29, item 20 / R11 / contract C6)
//
// Everything above answers "what appeared in the payload we just read". This
// half answers the question nobody was asking at all: **should we read?**
//
// ⛔ THE DEFECT (owner, 2026-08-10): a record created in another tab, by an
// automation, or by a connector sync does not appear until you reload. The
// rows fetch runs once per mount and re-runs only on ROWS_STALE_EVENT — and
// EVERY dispatcher of that event is this browser's own write path. Of the
// owner's three writers, only "another tab" emits anything, and only into the
// tab that did the writing. There is no polling, no revalidation, no
// visibilitychange and no BroadcastChannel anywhere in the client.
//
// The server now publishes a per-bucket revision that costs no deep copy
// (`GET /api/v1/changes`). These are the pure decisions taken on it, here
// rather than inside the effect so `verify_live_workspace.py` can run them
// under node — the same reason the merges above are pure.
// ===========================================================================

/** `{bucket: opaque token}`. A null means the backend publishes no revision for
 *  that bucket (Odoo-cached rows; a store backend that has none yet) — "do not
 *  poll this", which is a different fact from "unchanged". */
export type ChangeTokens = Record<string, string | null>;

/**
 * Which buckets genuinely changed between two observations.
 *
 * ⭐ A CHANGE IS REPORTED ONLY WHEN BOTH SIDES CARRY A NON-NULL TOKEN AND THEY
 * DIFFER. Every other case — the first observation, a poll that failed, a
 * bucket that has no token, a bucket appearing or disappearing from the map —
 * reports NOTHING, and the reasoning is asymmetric on purpose:
 *
 *   * a missed change costs one stale view until the next real write, which is
 *     exactly today's behaviour and therefore cannot be a regression;
 *   * a false change costs a full rows re-read, and a false change that repeats
 *     EVERY interval costs one per tab per 10 s — the melt this whole design
 *     exists to avoid.
 *
 * So the unknown cases resolve to "no", and each of them is a one-time
 * transition (first poll, a deploy adding a bucket, a backend flip) rather than
 * a standing condition. The alerts engine takes the identical `seeded` posture
 * server-side: its first evaluation raises nothing.
 */
export function changedBuckets(
  prev: ChangeTokens | null | undefined,
  next: ChangeTokens | null | undefined
): string[] {
  if (!prev || !next) return [];         // no baseline yet, or the poll failed
  const out: string[] = [];
  for (const [bucket, token] of Object.entries(next)) {
    if (typeof token !== "string" || token === "") continue;
    const before = prev[bucket];
    if (typeof before !== "string" || before === "") continue;   // baseline it
    if (before !== token) out.push(bucket);
  }
  return out;
}

/** What a set of changed buckets asks this tab to do. */
export interface ChangePlan {
  /** Drop this topic's rows memo and re-read the pool — the expensive one. */
  refetchRows: boolean;
  /** Re-read `/workspace` — views, fields, derived cells. The cheap one. */
  rereadWorkspace: boolean;
}

/**
 * ⛔ THE ROWS MEMO IS WHY THIS IS NOT JUST "REFETCH". `fetchTopicRows` holds a
 * FIVE-MINUTE per-topic memo, cleared only by the writing tab, so a refetch
 * triggered without dropping it is served from the copy that predates the very
 * change we detected: a poll that costs a request, reports success, and shows
 * the user nothing new. The caller must drop the memo for THIS topic —
 * `clearTopicRowsCache(topic.rowsPath)`, never `clearCustomersCache()`, which
 * would evict the other topic's window and re-download ~1 MB on the next
 * surface switch.
 *
 * An UNRECOGNISED bucket takes the CHEAP branch. A later server may publish a
 * bucket this build has never heard of (the shared overlay stratum is exactly
 * that case), and "something I do not understand changed" should cost a small
 * workspace read, never a pool download.
 */
export function planChangeReaction(changed: readonly string[]): ChangePlan {
  const plan: ChangePlan = { refetchRows: false, rereadWorkspace: false };
  for (const bucket of changed) {
    if (bucket === "rows") plan.refetchRows = true;
    else plan.rereadWorkspace = true;
  }
  return plan;
}

/**
 * The floor between two POOL re-reads of one topic. Only bites under sustained writing.
 *
 * ⛔ WHY A FLOOR IS NOT OPTIONAL, and the arithmetic is the same one that killed the naive design.
 * `user_tables.STORE_KEY` is ONE bucket holding EVERY `ut_*` table in a tenant, so the rows token
 * for every user table moves together — and while an automation upserts rows, or the relation
 * refresh commits, the token moves on every single interval. Without a floor each open tab would
 * then re-read the whole pool six times a minute, at three full-tenant deep copies per read: the
 * "two tabs saturate the server" case the poller was designed to avoid, reached through the
 * REFETCH instead of through the poll. Bounding cost per token request and leaving refetches
 * unbounded would just move the melt one step downstream.
 */
export const ROWS_REFETCH_FLOOR_MS = 30_000;

/**
 * How long to wait before re-reading this topic's pool: `0` = now.
 *
 * ⭐ IT COALESCES, IT NEVER DROPS. A caller that is told to wait must schedule the read for the
 * boundary, not discard the signal — several changes inside the window collapse into ONE read,
 * which is the same shape `routes_tables._refresh_relations` uses server-side and for the same
 * reason. Discarding would leave a tab stale for good if the burst ended right after a suppressed
 * change.
 *
 * ⚠ THE IDLE CASE IS UNAFFECTED, which is what keeps the owner's "about ten seconds" true: one
 * person adding one record hits a `lastAt` far in the past and re-reads immediately on the next
 * poll. The floor is only reachable when changes arrive faster than it.
 */
export function rowsRefetchDelay(lastAt: number, now: number,
                                 floorMs: number = ROWS_REFETCH_FLOOR_MS): number {
  if (!lastAt) return 0;                       // never read on this surface — go now
  const since = now - lastAt;
  return since >= floorMs ? 0 : floorMs - since;
}