import { createZstdDecompress } from 'node:zlib'

/**
 * Captures of niconico videos (`<unixtime>_nicovideo_jp_watch_sm<id>.tar.zst`,
 * one poster, ~190k files on homelab). The tar's first entry after its
 * directory is `server_response.metadata`: the site's API response for the
 * watch page, 30–70 KB, so the first article of the file holds it.
 */
export const NICOVIDEO_FILE = /^\d{9,11}_nicovideo_jp_watch_(sm\d+)\.tar\.zst$/i
export const NICOVIDEO_RELEASE = /^\d{9,11}_nicovideo_jp_watch_(sm\d+)$/i

export interface NicovideoInfo {
  id: string
  title: string
  owner: string | null
  registeredAt: string | null
  tags: string[]
}

/** As much of a zstd stream as `data` (a prefix of it) decompresses to. */
export function zstdPrefix(data: Buffer, maxBytes = 4 * 1024 * 1024): Promise<Buffer> {
  return new Promise((resolve) => {
    const out: Buffer[] = []
    let length = 0
    const z = createZstdDecompress()
    const done = () => resolve(Buffer.concat(out))
    z.on('data', (chunk: Buffer) => {
      out.push(chunk)
      length += chunk.length
      if (length >= maxBytes) z.destroy()
    })
    z.on('error', done)
    z.on('close', done)
    z.on('end', done)
    z.end(data)
  })
}

/** Entries at the start of a (possibly truncated) ustar archive. */
export function* tarEntries(tar: Buffer): Generator<{ name: string; data: Buffer }> {
  let offset = 0
  while (offset + 512 <= tar.length) {
    const header = tar.subarray(offset, offset + 512)
    const name = header.subarray(0, 100).toString('utf8').replace(/\0.*$/s, '')
    if (!name) return
    const prefix = header.subarray(345, 500).toString('utf8').replace(/\0.*$/s, '')
    const size = Number.parseInt(header.subarray(124, 136).toString('latin1').replace(/\0.*$/s, '').trim() || '0', 8) || 0
    yield { name: prefix ? `${prefix}/${name}` : name, data: tar.subarray(offset + 512, offset + 512 + size) }
    offset += 512 + Math.ceil(size / 512) * 512
  }
}

/** Title, uploader and tags from the start of a capture, or null when they aren't in it. */
export function nicovideoInfo(tar: Buffer): NicovideoInfo | null {
  for (const entry of tarEntries(tar)) {
    if (!entry.name.endsWith('/server_response.metadata')) continue
    try {
      const text = entry.data.toString('utf8')
      const json = JSON.parse(text.slice(text.indexOf('{')))
      const video = json?.data?.response?.video
      if (!video?.title) return null
      const owner = json.data.response.owner?.nickname ?? json.data.response.channel?.name ?? json.data.metadata?.jsonLds?.[0]?.author?.name ?? null
      const tags = (json.data.response.tag?.items ?? []).map((t: any) => String(t.name)).filter(Boolean)
      return { id: String(video.id ?? ''), title: String(video.title).trim(), owner: owner ? String(owner).trim() : null, registeredAt: video.registeredAt ?? null, tags }
    } catch {
      return null
    }
  }
  return null
}

/** Release name for a capture: `<title> - <uploader> (nicovideo sm123)`. */
export function nicovideoReleaseName(info: NicovideoInfo, fallbackId: string): string {
  const id = info.id || fallbackId
  return `${info.title}${info.owner ? ` - ${info.owner}` : ''} (nicovideo ${id})`
}