"use client";

import {
  createContext,
  useCallback,
  useContext,
  useEffect,
  useMemo,
  useRef,
  useState,
  type Dispatch,
  type ReactNode,
  type SetStateAction,
} from "react";

import type { AppSidebarControls, SidebarAccount } from "@/components/app-sidebar";
import type { SidebarSession } from "@/components/sidebar-session-row";
import { bindCurrentSubjectAccount, invalidateAccountFlight, invalidateSubjectCatalog, loadSubjectCatalog, readBootAccount, readCurrentSubjectAccountId, readCurrentSubjectId, subscribeCurrentSubject, useCurrentSubject } from "@/lib/current-subject";
import { sessionMatchesSubject } from "@/lib/chat-profile-picker-model";
import { readSessions } from "@/lib/home-cloud-sync";
import { clearHomeWarmSnapshot } from "@/lib/home-warm-snapshot";
import { prefetchHomeWarmDaily, prefetchHomeWarmSnapshot } from "@/lib/home-warm-prefetch";
import { isProfileComplete, readProfile } from "@/lib/home-profile";
import type { Account, ChatSession } from "@/lib/home-types";
import { BOOT_READ_INIT, bootSessionsPath, takeBootSessionsRead, withBootFallback } from "@/lib/boot-early-reads";
import { isListedSidebarSession } from "@/lib/session-list-filter";
import { toSidebarSessionRow } from "@/lib/session-sidebar-row";
import { mergeSubjectSessionRows } from "@/lib/subject-session-merge";

export type SessionListBoot = {
  readonly sessions: ChatSession[];
  readonly rawRows: unknown;
  readonly cursor: string | null;
  readonly account: Account | null;
  readonly signedOut: boolean;
  readonly subjectId?: string;
  readonly error?: string;
};

export type ShellRegistration = {
  readonly controls: AppSidebarControls;
  readonly escapeBlocked: boolean;
  readonly activeSessionId: string | null;
  readonly openingSessionId: string | null;
  readonly insetClassName: string;
  readonly insetInert: boolean;
  readonly sidebarSessions?: readonly SidebarSession[];
  readonly sidebarAccount?: SidebarAccount;
};

export type SessionListContextValue = {
  sessions: ChatSession[];
  setSessions: Dispatch<SetStateAction<ChatSession[]>>;
  sessionsCursor: string | null;
  setSessionsCursor: Dispatch<SetStateAction<string | null>>;
  account: Account | null;
  setAccount: Dispatch<SetStateAction<Account | null>>;
  signedOut: boolean;
  settled: boolean;
  ready: Promise<void>;
  waitUntilReady: () => Promise<void>;
  boot: () => SessionListBoot | null;
  reload: () => void;
  registerShellControls: (registration: ShellRegistration | null) => void;
};

const SessionListContext = createContext<SessionListContextValue | null>(null);
// Home produces these controls; only the shell subscribes to their updates.
// Publishing them through the data context re-renders Home, whose registration
// effect has fresh callbacks/rows, feeding another update back to the provider.
const ShellRegistrationContext = createContext<ShellRegistration | null>(null);

function createReadyGate(): { promise: Promise<void>; resolve: () => void } {
  let settle = () => {};
  const promise = new Promise<void>((resolve) => {
    settle = resolve;
  });
  return { promise, resolve: () => settle() };
}

function toSidebarAccount(account: Account | null): SidebarAccount | null {
  if (!account) return null;
  const profileName = account.profile && typeof account.profile === "object" && "name" in account.profile
    && typeof account.profile.name === "string" ? account.profile.name.trim() : "";
  const name = profileName;
  const email = account.user.email || "";
  return {
    name: name || email || "账户",
    email,
    initial: name.slice(0, 1) || email.slice(0, 1).toUpperCase() || "你",
    credits: account.credits,
    avatar: account.avatar,
  };
}

function sessionsToSidebarRows(sessions: readonly ChatSession[]): SidebarSession[] {
  return sessions.filter((session) => isListedSidebarSession(session)
    && sessionMatchesSubject(session, readCurrentSubjectId())).map((session) => toSidebarSessionRow(session));
}

function fetchSessionPage(subjectId: string, signal: AbortSignal): Promise<Response> {
  return fetch(bootSessionsPath(subjectId), { ...BOOT_READ_INIT, signal });
}

/**
 * Cold boot reads the account, the people list and the remembered person's
 * sessions in one round (BUG-1127). The sessions read is a guess at the
 * person: it is used only when the person is still the same once the people
 * list has settled the choice; otherwise it is dropped and the right person is
 * read, so another person's list never paints (task red line 3).
 */
export async function loadSessionList(signal: AbortSignal, forceCatalog = false): Promise<SessionListBoot> {
  const guessedSubject = readCurrentSubjectId();
  // On `/` the HTML already sent this read (T8); otherwise it starts here.
  const guessedSessions = withBootFallback(takeBootSessionsRead(guessedSubject), () => fetchSessionPage(guessedSubject, signal))
    .then((response) => ({ response, error: null as unknown }), (error: unknown) => ({ response: null, error }));
  void loadSubjectCatalog(forceCatalog).catch(() => undefined);
  const accountResult = await readBootAccount();
  signal.throwIfAborted();
  if (accountResult.status === 401) {
    clearHomeWarmSnapshot();
    invalidateSubjectCatalog();
    bindCurrentSubjectAccount("", null);
    return { sessions: [], rawRows: [], cursor: null, account: null, signedOut: true };
  }
  if (!accountResult.account) throw new Error("account_unavailable");
  const accountPayload = accountResult.account;
  const boundAccount = readCurrentSubjectAccountId();
  if (boundAccount !== accountPayload.user.id) {
    // Another account: nothing of the previous one may paint on `/` (BUG-1040).
    clearHomeWarmSnapshot();
    // With no account bound yet (first sign-in on this device, or after a
    // sign-out, which already invalidated), there is no stale people list; the
    // one started above was read with the current session, so keep it instead
    // of paying a second round for the same data (BUG-1127).
    if (boundAccount) invalidateSubjectCatalog();
    bindCurrentSubjectAccount(accountPayload.user.id, null);
  }
  // Joins the read started above unless the account change just invalidated it.
  await loadSubjectCatalog();
  signal.throwIfAborted();
  const subjectId = readCurrentSubjectId();
  // The guess was made for the account this device remembered; another account's
  // list is never reused, even for the same person id (task red line 8).
  const guessUsable = subjectId === guessedSubject && (!boundAccount || boundAccount === accountPayload.user.id);
  const guessed = guessUsable ? await guessedSessions : null;
  signal.throwIfAborted();
  const sessionResponse = guessed?.response ?? await fetchSessionPage(subjectId, signal);
  if (sessionResponse.status === 401) {
    clearHomeWarmSnapshot();
    return { sessions: [], rawRows: [], cursor: null, account: null, signedOut: true };
  }
  const sessionPayload = await sessionResponse.json().catch(() => null) as {
    sessions?: unknown;
    nextCursor?: unknown;
  } | null;
  if (!sessionResponse.ok) throw new Error("sessions_unavailable");
  const rawRows = Array.isArray(sessionPayload?.sessions) ? sessionPayload.sessions : [];
  const parsed = readSessions(rawRows, null);
  const cursor = typeof sessionPayload?.nextCursor === "string" ? sessionPayload.nextCursor : null;
  return {
    sessions: parsed.sessions,
    rawRows,
    cursor,
    account: accountPayload,
    signedOut: false,
    subjectId,
  };
}

export function SessionListProvider({ children }: { children: ReactNode }) {
  const [sessions, setSessions] = useState<ChatSession[]>([]);
  const [sessionsCursor, setSessionsCursor] = useState<string | null>(null);
  const [account, setAccount] = useState<Account | null>(null);
  const [signedOut, setSignedOut] = useState(false);
  const [settled, setSettled] = useState(false);
  const [registration, setRegistration] = useState<ShellRegistration | null>(null);
  const bootRef = useRef<SessionListBoot | null>(null);
  const controllerRef = useRef<AbortController | null>(null);
  const reloadRef = useRef<() => void>(() => undefined);
  const [readyPack] = useState(createReadyGate);
  const currentReady = useRef(readyPack);
  useCurrentSubject();

  useEffect(() => {
    let disposed = false;
    let displayedAccount = "";
    const load = (nextReadyPack: ReturnType<typeof createReadyGate>, forceCatalog = false) => {
      controllerRef.current?.abort();
      const controller = new AbortController();
      controllerRef.current = controller;
      setSettled(false);
      setSignedOut(false);
      bootRef.current = null;
      void loadSessionList(controller.signal, forceCatalog)
        .then((boot) => {
          if (disposed || controller.signal.aborted || controllerRef.current !== controller) return;
          const requestedSubject = boot.subjectId ?? readCurrentSubjectId();
          if (requestedSubject !== readCurrentSubjectId()) return;
          bootRef.current = boot;
          const sameAccount = Boolean(boot.account) && displayedAccount === boot.account?.user.id;
          setSessions((current) => sameAccount ? mergeSubjectSessionRows(current, boot.sessions, {
            subjectId: requestedSubject,
            complete: boot.cursor == null,
          }) : boot.sessions);
          displayedAccount = boot.account?.user.id ?? "";
          setSessionsCursor(boot.cursor);
          setAccount(boot.account);
          setSignedOut(boot.signedOut);
          setSettled(true);
          nextReadyPack.resolve();
        })
        .catch(() => {
          if (disposed || controller.signal.aborted || controllerRef.current !== controller) return;
          bootRef.current = { sessions: [], rawRows: [], cursor: null, account: null, signedOut: false, error: "session_list_unavailable" };
          setSettled(true);
          nextReadyPack.resolve();
        });
    };
    reloadRef.current = () => {
      const previous = currentReady.current;
      const next = createReadyGate();
      currentReady.current = next;
      previous.resolve();
      invalidateAccountFlight();
      load(next, true);
    };
    load(readyPack);
    const unsubscribe = subscribeCurrentSubject(() => {
      if (disposed) return;
      reloadRef.current();
    });
    return () => {
      disposed = true;
      unsubscribe();
      reloadRef.current = () => undefined;
      controllerRef.current?.abort();
    };
  }, []);

  // BUG-1104: a tab that opened on a secondary page has no warm snapshot yet,
  // so its first 「新建对话」 would cold-start Home. Once the list is settled and
  // no Home is mounted, fill the snapshot in the background (read-only GETs).
  // Home mounting, sign-out, an account switch or a list reload cancels it.
  const prefetchAccountId = settled && !signedOut && !registration && account && isProfileComplete(readProfile(account.profile))
    ? account.user.id
    : null;
  useEffect(() => {
    if (!prefetchAccountId || window.location.pathname === "/") return;
    const controller = new AbortController();
    const run = () => {
      const isCurrent = () => !controller.signal.aborted;
      void prefetchHomeWarmSnapshot(prefetchAccountId, isCurrent, undefined, controller.signal);
      // Only the account holder's own line: other people's profiles live in the
      // subject catalog, and a missing line there just keeps the old behaviour.
      if (readCurrentSubjectId() === "self" && account) {
        void prefetchHomeWarmDaily(prefetchAccountId, "self", readProfile(account.profile), isCurrent, undefined, controller.signal);
      }
    };
    // Safari has no requestIdleCallback; a short timeout keeps it off the first paint.
    const idle = "requestIdleCallback" in window;
    const handle = idle ? window.requestIdleCallback(run, { timeout: 2000 }) : window.setTimeout(run, 300);
    return () => {
      controller.abort();
      if (idle) window.cancelIdleCallback(handle);
      else window.clearTimeout(handle);
    };
  }, [account, prefetchAccountId]);

  const reload = useCallback(() => reloadRef.current(), []);

  const registerShellControls = useCallback((next: ShellRegistration | null) => {
    setRegistration(next);
  }, []);

  const boot = useCallback(() => bootRef.current, []);

  const waitUntilReady = useCallback(async () => {
    for (;;) {
      const gate = currentReady.current;
      await gate.promise;
      if (gate === currentReady.current) return;
    }
  }, []);
  const ready = readyPack.promise;
  const value = useMemo<SessionListContextValue>(() => ({
    sessions,
    setSessions,
    sessionsCursor,
    setSessionsCursor,
    account,
    setAccount,
    signedOut,
    settled,
    ready,
    waitUntilReady,
    boot,
    reload,
    registerShellControls,
  }), [
    account,
    boot,
    reload,
    registerShellControls,
    sessions,
    sessionsCursor,
    settled,
    signedOut,
    ready,
    waitUntilReady,
  ]);

  return (
    <SessionListContext.Provider value={value}>
      <ShellRegistrationContext.Provider value={registration}>
        {children}
      </ShellRegistrationContext.Provider>
    </SessionListContext.Provider>
  );
}

export function useSessionList(): SessionListContextValue {
  const value = useContext(SessionListContext);
  if (!value) {
    throw new Error("useSessionList must be used inside SessionListProvider");
  }
  return value;
}

export function useShellRegistration(): ShellRegistration | null {
  return useContext(ShellRegistrationContext);
}

export function sessionListSidebarModel(
  list: SessionListContextValue,
  registered: ShellRegistration | null,
): {
  sessions: readonly SidebarSession[];
  account: SidebarAccount | null;
} {
  return {
    sessions: registered?.sidebarSessions ?? sessionsToSidebarRows(list.sessions),
    account: registered?.sidebarAccount ?? toSidebarAccount(list.account),
  };
}