"use client";

/**
 * Chat conversations, kept in IndexedDB so history survives reloads and the
 * tab can be closed mid-conversation. The in-memory mirror makes reads
 * synchronous for React (`useSyncExternalStore`); writes update the mirror
 * immediately and persist asynchronously.
 *
 * Versioned DB `freezmo-chat` v1 with one store:
 *   chats  keyPath id   (index: updatedAt)
 *
 * Every stored record is validated with the shared zod schema, and the store
 * is capped (oldest conversations first) so a long-lived browser can't grow
 * without bound. Chats are part of the export/backup and the encrypted sync
 * payload — never the API key.
 */

import { chatConversationSchema, type ChatConversation, type ChatMessage } from "./schemas";
import { markSyncDirty } from "./sync-state";

const DB_NAME = "freezmo-chat";
const DB_VERSION = 1;
const CHATS = "chats";

/** Caps: a personal app, but still bounded. */
export const MAX_CONVERSATIONS = 100;
export const MAX_MESSAGES_PER_CHAT = 300;

const EMPTY: ChatConversation[] = [];

type Listener = () => void;

let conversations: ChatConversation[] = [];
let cached: ChatConversation[] = EMPTY;
const listeners = new Set<Listener>();
let hydrated = false;
let hydration: Promise<void> | null = null;

function notify(): void {
  cached = [...conversations].sort((a, b) => b.updatedAt - a.updatedAt);
  listeners.forEach((listener) => listener());
}

function openDb(): Promise<IDBDatabase> {
  return new Promise((resolve, reject) => {
    const request = indexedDB.open(DB_NAME, DB_VERSION);
    request.onupgradeneeded = () => {
      const db = request.result;
      if (!db.objectStoreNames.contains(CHATS)) {
        const store = db.createObjectStore(CHATS, { keyPath: "id" });
        store.createIndex("updatedAt", "updatedAt");
      }
    };
    request.onsuccess = () => resolve(request.result);
    request.onerror = () => reject(request.error);
  });
}

async function withDb<T>(_mode: IDBTransactionMode, run: (db: IDBDatabase) => T | Promise<T>): Promise<T> {
  const db = await openDb();
  try {
    return await run(db);
  } finally {
    window.setTimeout(() => db.close(), 1000);
  }
}

function requestToPromise<T>(request: IDBRequest<T>): Promise<T> {
  return new Promise((resolve, reject) => {
    request.onsuccess = () => resolve(request.result);
    request.onerror = () => reject(request.error);
  });
}

function persist(conversation: ChatConversation): void {
  void withDb("readwrite", (db) => {
    const transaction = db.transaction(CHATS, "readwrite");
    transaction.objectStore(CHATS).put(conversation);
  }).catch((error) => console.warn("[freezmo] could not save the chat", error));
}

function removeFromDb(id: string): void {
  void withDb("readwrite", (db) => {
    const transaction = db.transaction(CHATS, "readwrite");
    transaction.objectStore(CHATS).delete(id);
  }).catch((error) => console.warn("[freezmo] could not delete the chat", error));
}

/** Loads IndexedDB into the mirror exactly once. Safe to call repeatedly. */
export function ensureChatsHydrated(): Promise<void> {
  if (hydrated) return Promise.resolve();
  if (hydration) return hydration;
  hydration = (async () => {
    if (typeof indexedDB === "undefined") {
      hydrated = true;
      return;
    }
    try {
      await withDb("readonly", async (db) => {
        const transaction = db.transaction(CHATS, "readonly");
        const loaded = await requestToPromise(transaction.objectStore(CHATS).getAll() as IDBRequest<unknown[]>);
        const known = new Set(conversations.map((entry) => entry.id));
        const valid: ChatConversation[] = [];
        for (const raw of loaded) {
          const parsed = chatConversationSchema.safeParse(raw);
          if (!parsed.success) continue;
          if (known.has(parsed.data.id)) continue;
          valid.push(parsed.data);
        }
        conversations = [...conversations, ...valid]
          .sort((a, b) => b.updatedAt - a.updatedAt)
          .slice(0, MAX_CONVERSATIONS);
      });
    } catch (error) {
      console.warn("[freezmo] could not read the chat history", error);
    } finally {
      hydrated = true;
      notify();
    }
  })();
  return hydration;
}

export const chatHistoryStore = {
  subscribe(listener: Listener): () => void {
    listeners.add(listener);
    void ensureChatsHydrated();
    return () => listeners.delete(listener);
  },
  getSnapshot(): ChatConversation[] {
    return cached;
  },
  getServerSnapshot(): ChatConversation[] {
    return EMPTY;
  },
};

export function getConversation(id: string): ChatConversation | undefined {
  return conversations.find((entry) => entry.id === id);
}

export function conversationMessages(conversation: ChatConversation): ChatMessage[] {
  return conversation.messages.slice(-MAX_MESSAGES_PER_CHAT);
}

/** Creates or replaces one conversation and persists it. */
export function saveConversation(conversation: ChatConversation): void {
  const parsed = chatConversationSchema.safeParse({
    ...conversation,
    messages: conversation.messages.slice(-MAX_MESSAGES_PER_CHAT),
  });
  if (!parsed.success) {
    console.warn("[freezmo] skipping invalid chat", parsed.error.issues[0]);
    return;
  }
  const next = parsed.data;
  conversations = [next, ...conversations.filter((entry) => entry.id !== next.id)]
    .sort((a, b) => b.updatedAt - a.updatedAt)
    .slice(0, MAX_CONVERSATIONS);
  notify();
  persist(next);
  markSyncDirty();
}

export function renameConversation(id: string, title: string): void {
  const trimmed = title.trim().slice(0, 200);
  if (!trimmed) return;
  const current = getConversation(id);
  if (!current) return;
  saveConversation({ ...current, title: trimmed, updatedAt: Date.now() });
}

export function deleteConversation(id: string): void {
  conversations = conversations.filter((entry) => entry.id !== id);
  notify();
  removeFromDb(id);
  markSyncDirty();
}

/** Used by backup import and sync: wholesale replacement (no dirty marking —
    callers that need it wrap with withoutDirtyTracking). */
export function replaceChats(next: ChatConversation[]): void {
  const valid: ChatConversation[] = [];
  for (const raw of next) {
    const parsed = chatConversationSchema.safeParse(raw);
    if (parsed.success) valid.push(parsed.data);
  }
  conversations = valid.sort((a, b) => b.updatedAt - a.updatedAt).slice(0, MAX_CONVERSATIONS);
  notify();
  void withDb("readwrite", (db) => {
    const transaction = db.transaction(CHATS, "readwrite");
    transaction.objectStore(CHATS).clear();
    for (const conversation of conversations) transaction.objectStore(CHATS).put(conversation);
  }).catch((error) => console.warn("[freezmo] could not replace the chat history", error));
}