usenet-indexer/lib/release/identity.ts

import { hash as digest } from 'node:crypto'
import { looksLikeFilename } from '../headers/file_key.js'

export interface ReleaseIdentity {
  key: string
  /** Human-readable name: the subject text or the shared filename stem. */
  name: string
  /** Number of files announced by the `[i/M]` counter, when present. */
  fileTotal?: number
  /** Which rule recognised the release. */
  source: 'subject' | 'post' | 'stem' | 'weak-stem' | 'par2' | 'rar' | 'nzb' | 'spot'
}

export interface ReleaseInput {
  poster: string
  /** Subject without segment counter (the binary's `subject`). */
  subject: string
  /** Filename of the binary. */
  name: string
  /** True when the identity came from the yEnc body (obfuscated post). */
  weak: boolean
}

// Suffixes that differ between the files of one release. Stripped repeatedly,
// so "x.mkv.vol03+04.par2" and "x.part07.rar" both reduce to "x".
const SUFFIXES = [
  /\.vol\d+[+-]\d+\.par2$/i,
  /\.par2$/i,
  /\.part\d+\.rar$/i,
  /\.r\d{2,3}$/i,
  /\.rar$/i,
  /\.7z(\.\d{3})?$/i,
  /\.zip(\.\d{3})?$/i,
  // Split volumes (x.mkv.001), not codec names (H.264, H.265).
  /(?<=\.(7z|zip|rar|tar|mkv|mp4|avi|m4v|ts|m2ts|iso|img|bin|vob))\.\d{3}$/i,
  /\.(nfo|sfv|nzb|srr|srs|txt|jpg|png|md5|sha1|srt|sub|idx|ass|ssa|m3u|m3u8|cue|log)$/i,
  /\.tar$/i,
  /\.(zst|gz|xz|bz2)$/i,
  /\.(mkv|mp4|avi|m4v|ts|iso|img|bin|flac|mp3|epub|pdf)$/i,
]

/** Strips per-file suffixes (volume numbers, archive and par2 extensions) from a filename. */
export function fileStem(name: string): string {
  let stem = name.trim()
  let changed = true
  while (changed) {
    changed = false
    for (const suffix of SUFFIXES) {
      const next = stem.replace(suffix, '')
      if (next !== stem && next.length > 0) {
        stem = next
        changed = true
      }
    }
  }
  return stem
}

/**
 * What remains of a subject once the filename, counters, "yEnc" and sizes are
 * removed. Posters that name the release outside the quotes put it here.
 */
export function subjectRemainder(subject: string): string {
  return subject
    .replace(/"[^"]*"/g, ' ')
    .replace(/\[\d+\/\d+\]|\(\d+\/\d+\)/g, ' ')
    // File sizes follow "yEnc" at the end; other numbers (years, post ids) stay.
    .replace(/\byEnc\b(\s+\d+)?\s*$/i, ' ')
    .replace(/\byEnc\b/gi, ' ')
    .replace(/[\s\-–.:|]+/g, ' ')
    .trim()
}

/**
 * Posting tools put random per-file tokens and poster IDs in subjects (e.g.
 * `elys-de81bcabef5faf6a - [Nyh5Q07Y]`); only text that still reads like a
 * name once those are removed identifies a release.
 */
function isRandomToken(token: string): boolean {
  const t = token.replace(/^\[|\]$/g, '')
  if (t.length < 6) return false
  if (/^[0-9a-f]+$/i.test(t) && /\d/.test(t)) return true
  return /\d/.test(t) && /[a-z]/.test(t) && /[A-Z]/.test(t) && !/[._-]/.test(t)
}

/**
 * A stable per-post token: one short run of letters/digits with at least one
 * digit. Requiring a digit keeps constant labels like `[PRiVATE]` from
 * grouping different posts of the same poster.
 */
export function isPostToken(remainder: string): boolean {
  const compact = remainder.replace(/[\s\[\]()_-]+/g, '')
  return compact.length >= 6 && compact.length <= 40 && /\d/.test(compact) && /^[A-Za-z0-9]+$/.test(compact)
}

export function namesRelease(remainder: string): boolean {
  const words = remainder
    .split(/\s+/)
    .filter((w) => w && !isRandomToken(w))
    .join(' ')
  // At least two words of letters, joined the way release names are.
  return /[A-Za-z]{2,}[._ -]+[A-Za-z0-9]{2,}/.test(words)
}

function hash(...parts: (string | number | undefined)[]) {
  return digest('sha1', parts.map((p) => p ?? '').join('\n'))
}

/**
 * Decides which release (download) a file belongs to. Returns null when the
 * file cannot be grouped from its name alone (random extensionless names in
 * obfuscated posts; those need par2 matching). See CONCEPT.md (D16).
 */
export function releaseIdentity(input: ReleaseInput): ReleaseIdentity | null {
  const counter = /\[(\d+)\/(\d+)\]/.exec(input.subject)
  const fileTotal = counter ? Number.parseInt(counter[2], 10) : undefined
  const stem = fileStem(input.name)

  if (input.weak) {
    // Obfuscating posters randomise the poster per article; a real filename
    // stem is specific enough on its own.
    if (!looksLikeFilename(input.name)) return null
    return { key: hash('weak', stem), name: stem, source: 'weak-stem' }
  }

  // Text outside the quotes that names the release, e.g. "Some.Release [01/45] - "x.rar"".
  const remainder = subjectRemainder(input.subject)
  if (namesRelease(remainder)) {
    return {
      key: hash('subject', input.poster, remainder),
      name: remainder,
      fileTotal,
      source: 'subject',
    }
  }
  // Not a name, but a post id (e.g. `83110629-n [10/18] - "random"`): with the
  // [i/M] counter it groups the files of one post whose names are random.
  if (fileTotal && isPostToken(remainder)) {
    return { key: hash('post', input.poster, remainder, fileTotal), name: remainder, fileTotal, source: 'post' }
  }
  // The [i/M] total is informational, not part of the key: posters often
  // upload the par2 index without a counter, and it belongs to the same post.
  return { key: hash('stem', input.poster, stem), name: stem, fileTotal, source: 'stem' }
}

/** Release of a par2 recovery set; every file listed in it belongs to it. */
export function par2ReleaseIdentity(recoverySetId: string, fileNames: string[]): ReleaseIdentity {
  return { key: hash('par2', recoverySetId), name: par2ReleaseName(fileNames) ?? recoverySetId, source: 'par2' }
}

const SEPARATOR = /[._ -]/

/**
 * A release name from the files a par2 set lists. Files that differ only in
 * the middle (episodes S03E01…S03E20, parts) give their shared name, with
 * the episode reduced to the season: SEAL.Team.S03E01.1080p…-nitrato.mkv to
 * SEAL.Team.S03E20.1080p…-nitrato.mkv give SEAL.Team.S03.1080p…-nitrato.
 * Otherwise the longest stem, which tends to be the most descriptive (the
 * video file).
 */
export function par2ReleaseName(fileNames: string[]): string | undefined {
  const stems = [...new Set(fileNames.map((n) => fileStem(n.split(/[\\/]/).pop() ?? n)))].filter(Boolean)
  if (stems.length === 0) return undefined
  const longest = [...stems].sort((a, b) => b.length - a.length)[0]
  if (stems.length < 2) return longest

  let prefix = stems.reduce((p, s) => {
    let i = 0
    while (i < p.length && i < s.length && p[i] === s[i]) i++
    return p.slice(0, i)
  })
  let suffix = stems.reduce((p, s) => {
    let i = 0
    while (i < p.length && i < s.length && p[p.length - 1 - i] === s[s.length - 1 - i]) i++
    return p.slice(p.length - i)
  })
  const shortest = Math.min(...stems.map((s) => s.length))
  if (prefix.length + suffix.length > shortest) suffix = suffix.slice(prefix.length + suffix.length - shortest)

  // Season packs: "Show.S03E" → "Show.S03". Otherwise back to a whole token.
  const season = /^(.*[._ -]S\d{1,2})E\d*$/i.exec(prefix)
  if (season) prefix = season[1]
  else if (prefix.length < stems[0].length && !SEPARATOR.test(stems[0][prefix.length] ?? '.')) {
    prefix = prefix.replace(/[^._ -]*$/, '')
  }
  suffix = SEPARATOR.test(suffix[0] ?? '') ? suffix : suffix.replace(/^[^._ -]*/, '')
  prefix = prefix.replace(/[._ -]+$/, '')

  const name = suffix ? prefix + suffix : prefix
  // Only when the shared part carries most of the name (not just "The.").
  return name.length >= 8 && name.length >= 0.6 * shortest ? name : longest
}

/**
 * Release of a RAR volume set, from what its headers list: the shared
 * top-level directory if there is one, otherwise the first entry. For
 * volumes after the first, the first entry is the file that continues from
 * the previous volume, so all volumes of a single-file archive agree.
 */
/**
 * Folder and file names that say nothing about what a release is: disc
 * structures (VIDEO_TS on every DVD), samples, subtitles, disc numbers.
 * Kept in step with SQL's is_readable_name().
 */
export const GENERIC_NAMES = /^(video_ts|audio_ts|bdmv|certificate|hvdvd_ts|samples?|subs?|subtitles?|proof|cover|covers|extras?|featurettes?|(cd|dvd|disc|disk)[ ._-]?\d{1,2})$/i

export function isGenericName(name: string): boolean {
  return GENERIC_NAMES.test(name.trim())
}

export function rarReleaseIdentity(entries: { name: string; size: number | null }[]): ReleaseIdentity | null {
  if (entries.length === 0) return null
  const tops = new Set(entries.map((e) => e.name.split(/[\\/]/)[0]))
  const nested = entries.some((e) => /[\\/]/.test(e.name))
  // A generic top folder (VIDEO_TS) is shared by unrelated archives: key on the first entry instead.
  if (nested && tops.size === 1 && !isGenericName([...tops][0])) {
    const [top] = tops
    return { key: hash('rar-dir', top), name: top, source: 'rar' }
  }
  const first = entries[0]
  const base = first.name.split(/[\\/]/).pop() ?? first.name
  return { key: hash('rar-entry', first.name, first.size ?? ''), name: fileStem(base), source: 'rar' }
}