'use client';

// ==================== 持久化适配器 ====================
// 统一的存储接口：优先使用服务端文件系统，fallback 到浏览器 IndexedDB/localStorage
// 多用户隔离：首次访问自动生成 userId 并存入 cookie

import { get, set, del } from 'idb-keyval';

// ==================== 用户ID管理 ====================

function getUserId() {
    if (typeof document === 'undefined') return null;
    const match = document.cookie.match(/author-uid=([a-zA-Z0-9_-]+)/);
    return match ? match[1] : null;
}

function ensureUserId() {
    let uid = getUserId();
    if (!uid) {
        uid = 'u-' + Date.now().toString(36) + Math.random().toString(36).slice(2, 8);
        // 设置 365 天有效的 cookie（HttpOnly = false，前端可读）
        document.cookie = `author-uid=${uid}; path=/; max-age=${365 * 24 * 3600}; SameSite=Lax`;
    }
    return uid;
}

// ==================== 服务端存储 ====================

let _serverAvailable = null; // null = 未检测, true/false = 检测结果

async function checkServerAvailable() {
    if (_serverAvailable !== null) return _serverAvailable;
    try {
        const res = await fetch('/api/storage?key=__ping', {
            method: 'GET',
            credentials: 'include',
        });
        _serverAvailable = res.ok || res.status === 401; // 401 也说明服务端在运行
        return _serverAvailable;
    } catch {
        _serverAvailable = false;
        return false;
    }
}

async function serverGet(key) {
    const res = await fetch(`/api/storage?key=${encodeURIComponent(key)}`, {
        method: 'GET',
        credentials: 'include',
    });
    if (!res.ok) throw new Error(`Server GET failed: ${res.status}`);
    const { data } = await res.json();
    return data;
}

async function serverSet(key, value) {
    const res = await fetch('/api/storage', {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        credentials: 'include',
        body: JSON.stringify({ key, value }),
    });
    if (!res.ok) throw new Error(`Server POST failed: ${res.status}`);
}

async function serverDel(key) {
    const res = await fetch(`/api/storage?key=${encodeURIComponent(key)}`, {
        method: 'DELETE',
        credentials: 'include',
    });
    if (!res.ok) throw new Error(`Server DELETE failed: ${res.status}`);
}

// ==================== 统一存储接口 ====================

/**
 * 读取数据（服务端优先，fallback 到 IndexedDB）
 * @param {string} key - 存储键名
 * @returns {Promise<any>} 存储的值，不存在时返回 undefined
 */
export async function persistGet(key) {
    if (typeof window === 'undefined') return undefined;
    ensureUserId();

    try {
        if (await checkServerAvailable()) {
            const data = await serverGet(key);
            if (data !== null && data !== undefined) return data;
            // 服务端没有，尝试从浏览器迁移
            const localData = await browserGet(key);
            if (localData !== null && localData !== undefined) {
                // 自动迁移到服务端
                await serverSet(key, localData).catch(() => { });
                return localData;
            }
            return undefined;
        }
    } catch {
        // 服务端失败，降级到浏览器
    }

    return await browserGet(key);
}

/**
 * 写入数据（同时写入服务端和浏览器）
 * @param {string} key - 存储键名
 * @param {any} value - 要存储的值
 */
export async function persistSet(key, value) {
    if (typeof window === 'undefined') return;
    ensureUserId();

    // 先写浏览器（立即可用）
    await browserSet(key, value);

    // 异步写服务端（不阻塞 UI）
    if (await checkServerAvailable()) {
        serverSet(key, value).catch(err => {
            console.warn('[persist] Server write failed, data saved in browser only:', err.message);
        });
    }
}

/**
 * 删除数据
 * @param {string} key - 存储键名
 */
export async function persistDel(key) {
    if (typeof window === 'undefined') return;

    await browserDel(key);

    if (await checkServerAvailable()) {
        serverDel(key).catch(() => { });
    }
}

// ==================== 浏览器存储桥接 ====================

// 大数据用 IndexedDB，小数据用 localStorage
const LOCALSTORAGE_KEYS = new Set([
    'author-project-settings',
    'author-active-work',
    'author-token-stats',
    'author-theme',
    'author-lang',
    'author-visual',
    'author-onboarding-done',
    'author-context-selection',
    'author-api-profiles',
    'author-delete-never-remind',
    'author-delete-skip-today',
]);

async function browserGet(key) {
    if (LOCALSTORAGE_KEYS.has(key)) {
        const raw = localStorage.getItem(key);
        if (raw === null) return undefined;
        try { return JSON.parse(raw); } catch { return raw; }
    }
    const val = await get(key);
    return val === undefined ? undefined : val;
}

async function browserSet(key, value) {
    if (LOCALSTORAGE_KEYS.has(key)) {
        localStorage.setItem(key, typeof value === 'string' ? value : JSON.stringify(value));
        return;
    }
    await set(key, value);
}

async function browserDel(key) {
    if (LOCALSTORAGE_KEYS.has(key)) {
        localStorage.removeItem(key);
        return;
    }
    await del(key);
}

// ==================== 便捷方法 ====================

/**
 * 同步读取 localStorage（仅用于需要同步值的场景，如初始化 zustand store）
 * 不走服务端。
 */
export function persistGetSync(key) {
    if (typeof window === 'undefined') return undefined;
    const raw = localStorage.getItem(key);
    if (raw === null) return undefined;
    try { return JSON.parse(raw); } catch { return raw; }
}

/**
 * 初始化：确保 userId 存在，并触发服务端可用性检测
 * 应在应用启动时调用一次
 */
export async function initPersistence() {
    if (typeof window === 'undefined') return;
    ensureUserId();
    await checkServerAvailable();
}