// 檔案系統與時鐘皆由外部注入；核心只依賴這兩個介面
export interface Fs {
  read(path: string): Promise<string | null>
  write(path: string, data: string): Promise<void>
  /** 沒有 rename 的環境（hooks 沙箱）會直接覆寫 */
  rename?(from: string, to: string): Promise<void>
  list(dir: string): Promise<string[]>
}

export type Clock = { now(): number }

// 先寫暫存檔再 rename，當機時不會留下寫到一半的檔案
export async function writeAtomic(fs: Fs, path: string, data: string): Promise<void> {
  if (!fs.rename) return fs.write(path, data)
  const tmp = `${path}.tmp`
  await fs.write(tmp, data)
  await fs.rename(tmp, path)
}

export async function readJson<T>(fs: Fs, path: string): Promise<T | null> {
  const raw = await fs.read(path)
  if (raw === null) return null
  try {
    return JSON.parse(raw) as T
  } catch {
    return null
  }
}

export const writeJson = (fs: Fs, path: string, value: unknown) => writeAtomic(fs, path, JSON.stringify(value, null, 2))

export function memoryFs(seed: Record<string, string> = {}): Fs & { files: Map<string, string> } {
  const files = new Map(Object.entries(seed))
  return {
    files,
    async read(path) {
      return files.get(path) ?? null
    },
    async write(path, data) {
      files.set(path, data)
    },
    async rename(from, to) {
      const v = files.get(from)
      if (v === undefined) throw new Error(`ENOENT: ${from}`)
      files.delete(from)
      files.set(to, v)
    },
    async list(dir) {
      const prefix = dir.endsWith('/') ? dir : dir + '/'
      const names = new Set<string>()
      for (const k of files.keys()) if (k.startsWith(prefix)) names.add(k.slice(prefix.length).split('/')[0]!)
      return [...names].filter(n => !n.endsWith('.tmp')).sort()
    },
  }
}

export function fakeClock(start = Date.parse('2026-10-12T00:00:00Z')) {
  let t = start
  return { now: () => t, advance: (ms: number) => void (t += ms), set: (ms: number) => void (t = ms) }
}