"use client";

import { useEffect, useSyncExternalStore } from "react";

import { fetchCloudChartLibrary } from "@/lib/home-cloud-sync";
import { readProfile, upsertSelfChart } from "@/lib/home-profile";
import type { Account, ChartLibraryRecord, Profile } from "@/lib/home-types";

const SELF_SUBJECT_ID = "self";
export const LAST_SUBJECT_ACCOUNT_KEY = "jyotisha_current_subject_account";

export function currentSubjectStorageKey(id: string): string {
  return `jyotisha_current_subject:${id}`;
}

function storedValue(key: string): string {
  try {
    return typeof localStorage === "undefined" ? "" : localStorage.getItem(key) || "";
  } catch {
    return "";
  }
}

function storeValue(key: string, value: string): void {
  try {
    if (typeof localStorage !== "undefined") localStorage.setItem(key, value);
  } catch { /* The in-memory selection still works when storage is unavailable. */ }
}

let accountId = storedValue(LAST_SUBJECT_ACCOUNT_KEY);
let subjectId = (accountId && storedValue(currentSubjectStorageKey(accountId))) || SELF_SUBJECT_ID;
let catalogReady = false;
let catalog: ChartLibraryRecord[] | null = null;
const listeners = new Set<() => void>();
const catalogListeners = new Set<() => void>();

export function readCurrentSubjectId(): string {
  return subjectId;
}

export function readCurrentSubjectAccountId(): string {
  return accountId;
}

export function peekSubjectCatalog(): readonly ChartLibraryRecord[] | null {
  return catalogReady ? catalog : null;
}

export function readCurrentSubjectScope(): string {
  return JSON.stringify([accountId, subjectId]);
}

export function useCurrentSubjectScope(): string {
  return useSyncExternalStore((listener) => {
    const offSubject = subscribeCurrentSubject(listener);
    const offCatalog = subscribeSubjectCatalog(listener);
    return () => { offSubject(); offCatalog(); };
  }, readCurrentSubjectScope, () => "");
}

export function currentSubjectCatalogReady(): boolean {
  return catalogReady;
}

export function subscribeCurrentSubject(listener: () => void): () => void {
  listeners.add(listener);
  return () => { listeners.delete(listener); };
}

export function subscribeSubjectCatalog(listener: () => void): () => void {
  catalogListeners.add(listener);
  return () => { catalogListeners.delete(listener); };
}

function emit(): void {
  for (const listener of listeners) listener();
}

function emitCatalog(): void {
  for (const listener of catalogListeners) listener();
}

export function setCurrentSubject(next: string): void {
  const id = next.trim() || SELF_SUBJECT_ID;
  if (id === subjectId) return;
  subjectId = id;
  if (accountId) storeValue(currentSubjectStorageKey(accountId), id);
  emit();
}

/** A null list preserves the stored choice, but cannot open the request gate. */
export function bindCurrentSubjectAccount(nextAccountId: string, knownOtherIds: readonly string[] | null): void {
  const previousReady = catalogReady;
  const previousAccount = accountId;
  accountId = nextAccountId;
  const stored = nextAccountId ? storedValue(currentSubjectStorageKey(nextAccountId)) || SELF_SUBJECT_ID : SELF_SUBJECT_ID;
  const valid = stored === SELF_SUBJECT_ID || knownOtherIds === null || knownOtherIds.includes(stored);
  const next = valid ? stored : SELF_SUBJECT_ID;
  if (nextAccountId) {
    storeValue(LAST_SUBJECT_ACCOUNT_KEY, nextAccountId);
    if (!valid) storeValue(currentSubjectStorageKey(nextAccountId), SELF_SUBJECT_ID);
    try { localStorage.removeItem(`jyotisha_active_chart:${nextAccountId}`); } catch { /* Optional storage. */ }
  }
  catalogReady = Boolean(nextAccountId) && knownOtherIds !== null;
  if (next !== subjectId) {
    subjectId = next;
    emit();
  }
  if (previousReady !== catalogReady || previousAccount !== accountId) emitCatalog();
}

export function useCurrentSubject(): string {
  return useSyncExternalStore(subscribeCurrentSubject, readCurrentSubjectId, () => SELF_SUBJECT_ID);
}

export function useCurrentSubjectReady(): boolean {
  const ready = useSyncExternalStore(subscribeSubjectCatalog, currentSubjectCatalogReady, () => false);
  useEffect(() => {
    if (currentSubjectCatalogReady()) return;
    void loadSubjectCatalog().catch(() => undefined);
  }, []);
  return ready;
}

export function useCurrentSubjectProfile(self: Profile): Profile | null {
  const id = useCurrentSubject();
  const rows = useSyncExternalStore(subscribeSubjectCatalog, () => catalog, () => null);
  return id === SELF_SUBJECT_ID ? self : rows?.find((row) => row.id === id)?.profile ?? null;
}

let catalogRequest: Promise<ChartLibraryRecord[]> | null = null;
let catalogAccountId = "";
let catalogGeneration = 0;
let othersUnavailable = false;
let accountFlight: Promise<{ status: number; account: Account | null }> | null = null;
let recoveryTimer: ReturnType<typeof setTimeout> | null = null;

export function subjectCatalogOthersUnavailable(): boolean {
  return othersUnavailable;
}

export function invalidateAccountFlight(): void {
  accountFlight = null;
}

/** One in-flight account read shared by the session list and the person catalog. */
export function readBootAccount(): Promise<{ status: number; account: Account | null }> {
  if (accountFlight) return accountFlight;
  const published = (async () => {
    const response = await fetch("/api/account", { cache: "no-store" });
    if (response.status === 401) return { status: 401, account: null };
    const payload = await response.json().catch(() => null);
    if (!response.ok) throw new Error("account_unavailable");
    return { status: response.status, account: payload as Account };
  })().catch((error: unknown) => {
    if (accountFlight === published) accountFlight = null;
    throw error;
  });
  accountFlight = published;
  return published;
}

function clearCatalogRecovery(): void {
  if (recoveryTimer === null) return;
  clearTimeout(recoveryTimer);
  recoveryTimer = null;
}

export function resetSubjectCatalogForTests(): void {
  catalogGeneration += 1;
  catalogRequest = null;
  catalogAccountId = "";
  accountId = "";
  subjectId = SELF_SUBJECT_ID;
  catalogReady = false;
  catalog = null;
  othersUnavailable = false;
  accountFlight = null;
  clearCatalogRecovery();
}

export function invalidateSubjectCatalog(): void {
  catalogGeneration += 1;
  catalogRequest = null;
  catalogAccountId = "";
  catalogReady = false;
  catalog = null;
  othersUnavailable = false;
  clearCatalogRecovery();
  emitCatalog();
}

function rememberCatalog(account: Account, library: ChartLibraryRecord[], degraded: boolean): ChartLibraryRecord[] {
  catalogAccountId = account.user.id;
  catalog = library;
  othersUnavailable = degraded;
  bindCurrentSubjectAccount(catalogAccountId, degraded ? [] : library.filter((row) => row.role === "other").map((row) => row.id));
  emitCatalog();
  return library;
}

function scheduleCatalogRecovery(account: Account): void {
  if (recoveryTimer !== null || !othersUnavailable) return;
  const generation = catalogGeneration;
  const timer = setTimeout(() => {
    recoveryTimer = null;
    if (generation !== catalogGeneration || !othersUnavailable) return;
    void fetchCloudChartLibrary().then((others) => {
      if (generation !== catalogGeneration) return;
      const self = readProfile(account.profile);
      const library = upsertSelfChart(others.filter((row) => row.role === "other"), self);
      clearCatalogRecovery();
      catalogRequest = Promise.resolve(rememberCatalog(account, library, false));
    }).catch(() => {
      if (generation === catalogGeneration && othersUnavailable) scheduleCatalogRecovery(account);
    });
  }, 3000);
  if (typeof timer === "object" && timer && "unref" in timer) timer.unref();
  recoveryTimer = timer;
}

type SettledRead<T> = { ok: true; value: T } | { ok: false; error: unknown };

/** Starts a read now without an unhandled rejection; the caller rethrows on unwrap. */
function settledRead<T>(promise: Promise<T>): Promise<SettledRead<T>> {
  return promise.then((value) => ({ ok: true as const, value }), (error: unknown) => ({ ok: false as const, error }));
}

function unwrapRead<T>(read: SettledRead<T>): T {
  if (!read.ok) throw read.error;
  return read.value;
}

export function loadSubjectCatalog(force = false): Promise<ChartLibraryRecord[]> {
  if (!force && catalogRequest) return catalogRequest;
  const generation = ++catalogGeneration;
  clearCatalogRecovery();
  // The people list does not depend on the account payload, so it is read in the
  // same round as the account instead of after it (BUG-1127).
  const libraryRead = settledRead(fetchCloudChartLibrary());
  catalogRequest = readBootAccount().then(async (result) => {
    if (generation !== catalogGeneration) return loadSubjectCatalog();
    if (result.status === 401 || !result.account) throw new Error("account_unavailable");
    const account = result.account;
    try {
      const others = unwrapRead(await libraryRead);
      if (generation !== catalogGeneration) return loadSubjectCatalog();
      const self = readProfile(account.profile);
      const library = upsertSelfChart(others.filter((row) => row.role === "other"), self);
      return rememberCatalog(account, library, false);
    } catch (error) {
      if (generation !== catalogGeneration) throw error;
      const self = readProfile(account.profile);
      const library = upsertSelfChart([], self);
      const remembered = rememberCatalog(account, library, true);
      scheduleCatalogRecovery(account);
      return remembered;
    }
  }).catch((error: unknown) => {
    if (generation === catalogGeneration) catalogRequest = null;
    throw error;
  });
  return catalogRequest;
}