import { readFile, stat, writeFile, rename, readdir, unlink } from 'fs/promises'
import { join, extname, dirname, basename } from 'path'
import type { ReadFileResult, SaveFileResult, FileNode } from '../shared/types'

const MAX_FILE_SIZE = 20 * 1024 * 1024 // 20MB
const ALLOWED_EXTENSIONS = new Set(['.md', '.markdown', '.txt'])
const SKIP_DIRS = new Set([
  'node_modules', '.git', '.svn', '.hg', 'dist', 'out',
  '.next', '.nuxt', '__pycache__', '.DS_Store'
])

export async function readFileContent(filePath: string): Promise<ReadFileResult> {
  try {
    const fileStat = await stat(filePath)
    if (fileStat.size > MAX_FILE_SIZE) {
      return { success: false, error: `文件过大（${(fileStat.size / 1024 / 1024).toFixed(1)} MB），暂不支持超过 20MB 的文件` }
    }
    let content = await readFile(filePath, 'utf-8')
    if (content.charCodeAt(0) === 0xFEFF) content = content.slice(1)
    return { success: true, content }
  } catch (err) {
    return { success: false, error: (err as Error).message }
  }
}

// C-02: 临时文件写到与目标相同目录（避免跨盘 rename 失败）
export async function saveFileContent(filePath: string, content: string): Promise<SaveFileResult> {
  const tmpFile = join(dirname(filePath), `.marklite-tmp-${Date.now()}-${basename(filePath)}`)
  try {
    await writeFile(tmpFile, content, 'utf-8')
    await rename(tmpFile, filePath)
    return { success: true, filePath }
  } catch (err) {
    // 清理残留临时文件
    try { await unlink(tmpFile) } catch { /* ignore */ }
    return { success: false, error: (err as Error).message }
  }
}

// M-05: 递归深度限制 + 错误边界
export async function buildDirTree(dirPath: string, depth = 0, maxDepth = 10): Promise<FileNode[]> {
  if (depth > maxDepth) return []

  let entries
  try {
    entries = await readdir(dirPath, { withFileTypes: true })
  } catch {
    return []
  }

  entries.sort((a, b) => {
    if (a.isDirectory() && !b.isDirectory()) return -1
    if (!a.isDirectory() && b.isDirectory()) return 1
    return a.name.localeCompare(b.name)
  })

  const children: FileNode[] = []
  for (const entry of entries) {
    if (SKIP_DIRS.has(entry.name)) continue
    if (entry.name.startsWith('.')) continue

    const childPath = join(dirPath, entry.name)
    if (entry.isDirectory()) {
      const subChildren = await buildDirTree(childPath, depth + 1, maxDepth)
      if (subChildren.length > 0) {
        children.push({ name: entry.name, path: childPath, type: 'dir', children: subChildren })
      }
    } else {
      const ext = extname(entry.name).toLowerCase()
      if (ALLOWED_EXTENSIONS.has(ext)) {
        children.push({ name: entry.name, path: childPath, type: 'file' })
      }
    }
  }
  return children
}