import { useEffect, useMemo, useRef, useState } from "react";
import AsyncStorage from "@react-native-async-storage/async-storage";

export type Todo = {
  id: string;
  title: string;
  done: boolean;
  createdAt: number;
};

const STORAGE_KEY = "todos.v1";
const DEBOUNCE_MS = 300;

export function useTodos() {
  const [todos, setTodos] = useState<Todo[]>([]);
  const timer = useRef<ReturnType<typeof setTimeout> | null>(null);

  // load once
  useEffect(() => {
    (async () => {
      const raw = await AsyncStorage.getItem(STORAGE_KEY);
      if (raw) setTodos(JSON.parse(raw));
    })();
  }, []);

  // debounce save
  useEffect(() => {
    if (timer.current) clearTimeout(timer.current);
    timer.current = setTimeout(() => {
      AsyncStorage.setItem(STORAGE_KEY, JSON.stringify(todos)).catch((e) => {
        console.warn("Debounce warn: ", e);
      });
    }, DEBOUNCE_MS);

    return () => {
      if (timer.current) clearTimeout(timer.current);
    };
  }, [todos]);

  const activeTodos = useMemo(() => todos.filter((t) => !t.done), [todos]);
  const doneTodos = useMemo(() => todos.filter((t) => t.done), [todos]);
  const leftCount = useMemo(() => activeTodos.length, [activeTodos]);

  const add = (title: string) => {
    const t = title.trim();
    if (!t) return;
    const id = `${Date.now}-${Math.random().toString(36).slice(2, 8)}`;
    setTodos([
      {
        id,
        title: t,
        done: false,
        createdAt: Date.now(),
      },
      ...todos,
    ]);
  };

  const toggle = (id: string) =>
    setTodos(
      todos.map((it) =>
        it.id === id
          ? {
              ...it,
              done: !it.done,
            }
          : it
      )
    );

  const remove = (id: string) => setTodos(todos.filter((it) => it.id !== id));

  const clearDone = () => setTodos(todos.filter((it) => !it.done));

  const completeAll = () =>
    setTodos(todos.map((it) => ({ ...it, done: true })));

  return {
    todos,
    setTodos,
    activeTodos,
    doneTodos,
    leftCount,
    add,
    toggle,
    remove,
    clearDone,
    completeAll,
  };
}