/**
 * 文件索引管理器
 * 支持多种文件索引加载方式：
 * 1. CLI 环境：从 /__CONTENT_INDEX.json 加载
 * 2. Dev 环境：使用 webpackContext 仅加载 .md 文件
 * 3. 浏览器环境：用户选择本地文件夹，扫描文件索引
 *      - 支持 IndexedDB 持久化目录句柄，刷新页面无需重新选择
 */

import {
  saveHandle,
  loadHandle,
  removeHandle,
  ensurePermission,
} from "./file-index-db";

type FileIndex = Record<string, string>;

let fileIndex: FileIndex | null = null;
let indexLoadPromise: Promise<void> | null = null;
let activeSource: "cli" | "webpack" | "folder" | null = null;

/** Currently active directory handle (if folder source) */
let activeDirHandle: FileSystemDirectoryHandle | null = null;

/**
 * 加载文件索引（只加载一次）
 * 尝试顺序：CLI JSON → webpack context → 已持久化的目录句柄
 */
function ensureIndexLoaded(): Promise<void> {
  if (indexLoadPromise) return indexLoadPromise;

  indexLoadPromise = (async () => {
    // 策略 1: CLI 环境 — 从 /__CONTENT_INDEX.json 加载
    try {
      const response = await fetch("/__CONTENT_INDEX.json");
      if (response.ok) {
        const index = await response.json();
        fileIndex = { ...fileIndex, ...index };
        activeSource = "cli";
        return;
      }
    } catch (e) {
      // CLI 索引不可用时尝试下一个策略
    }

    // 策略 2: Dev 环境 — webpackContext + raw loader
    try {
      const context = import.meta.webpackContext("../../content", {
        recursive: true,
        regExp: /\.md|\.yarn|\.csv$/i,
      });
      const keys = context.keys();
      const index: FileIndex = {};
      for (const key of keys) {
        const module = context(key) as { default?: string } | string;
        const content =
          typeof module === "string" ? module : (module.default ?? "");
        const normalizedPath = "/content" + key.slice(1);
        index[normalizedPath] = content;
      }
      fileIndex = { ...fileIndex, ...index };
      activeSource = "webpack";
    } catch (e) {
      // webpackContext 不可用时忽略
    }

    // 策略 3: 浏览器 — 尝试从 IndexedDB 恢复保存的目录句柄
    if (!activeSource) {
      try {
        const restored = await restoreSavedHandle();
        if (restored) {
          activeSource = "folder";
          return;
        }
      } catch (e) {
        // 无法恢复，继续 — 用户需要手动选择文件夹
      }
    }
  })();

  return indexLoadPromise;
}

/**
 * 扫描文件系统目录，构建文件索引
 * 递归扫描，仅索引 .md / .yarn / .csv 文件
 */
async function scanDirectory(
  handle: FileSystemDirectoryHandle,
  prefix = "",
): Promise<FileIndex> {
  const index: FileIndex = {};
  const acceptedExt = /\.(md|yarn|csv)$/i;

  for await (const [name, entry] of (handle as any).entries()) {
    if (entry.kind === "directory") {
      const sub = await scanDirectory(
        entry as FileSystemDirectoryHandle,
        prefix + name + "/",
      );
      Object.assign(index, sub);
    } else if (entry.kind === "file" && acceptedExt.test(name)) {
      const file = await (entry as FileSystemFileHandle).getFile();
      const path = prefix + name;
      index[path] = await file.text();
    }
  }

  return index;
}

/**
 * 尝试从 IndexedDB 恢复之前保存的目录句柄并加载内容
 */
async function restoreSavedHandle(): Promise<boolean> {
  if (typeof indexedDB === "undefined") return false;

  const handle = await loadHandle();
  if (!handle) return false;

  const permitted = await ensurePermission(handle);
  if (!permitted) return false;

  try {
    const index = await scanDirectory(handle);
    fileIndex = { ...fileIndex, ...index };
    activeDirHandle = handle;
    // Refresh the promise so future calls use new index
    indexLoadPromise = Promise.resolve();
    return true;
  } catch {
    // handle is stale (folder moved/deleted), clear it
    await removeHandle();
    return false;
  }
}

/**
 * 让用户选择本地文件夹并加载文件索引 (Browser only)
 * 会持久化目录句柄到 IndexedDB，刷新后自动恢复。
 *
 * @returns 索引中的文件路径数组，失败返回 null
 */
export async function loadFromUserFolder(): Promise<string[] | null> {
  if (!("showDirectoryPicker" in window)) {
    console.warn("showDirectoryPicker not supported in this browser");
    return null;
  }

  try {
    const handle = await window.showDirectoryPicker({ mode: "read" });
    const index = await scanDirectory(handle);

    // Replace the existing index entirely with the user's folder content
    fileIndex = index;
    activeDirHandle = handle;
    activeSource = "folder";
    // Reset the load promise so future ensureIndexLoaded() calls are no-ops
    indexLoadPromise = Promise.resolve();

    await saveHandle(handle);

    return Object.keys(index);
  } catch (err) {
    // User cancelled or error
    if ((err as DOMException)?.name !== "AbortError") {
      console.error("Failed to load folder:", err);
    }
    return null;
  }
}

/**
 * 移除已保存的目录句柄，并清除索引
 * 之后确保索引加载时回退到 CLI/webpack 策略
 */
export async function switchToBuiltInSource(): Promise<void> {
  await removeHandle();
  activeDirHandle = null;
  fileIndex = null;
  indexLoadPromise = null;
  activeSource = null;
}

/**
 * 获取当前激活的内容源
 */
export function getActiveSource(): string | null {
  return activeSource;
}

/**
 * 从索引获取文件内容
 */
export async function getIndexedData(path: string): Promise<string> {
  await ensureIndexLoaded();
  if (fileIndex && fileIndex[path]) {
    return fileIndex[path];
  }
  const res = await fetch(path);
  const content = await res.text();
  fileIndex = fileIndex || {};
  fileIndex[path] = content;
  return content;
}

/**
 * 获取指定扩展名的文件路径
 */
export async function getPathsByExtension(ext: string): Promise<string[]> {
  await ensureIndexLoaded();
  if (!fileIndex) return [];
  const normalizedExt = ext.startsWith(".") ? ext : `.${ext}`;
  return Object.keys(fileIndex).filter((path) =>
    path.toLowerCase().endsWith(normalizedExt.toLowerCase()),
  );
}

/**
 * 清除索引（用于测试或重新加载）
 */
export function clearIndex(): void {
  fileIndex = null;
  indexLoadPromise = null;
  activeSource = null;
  activeDirHandle = null;
}