import { createHash } from 'node:crypto'

/**
 * Identity of one uploaded file: every segment of it has the same poster, the
 * same subject apart from the segment counter, and the same segment count.
 * The group is deliberately left out so crossposts resolve to one file.
 * See CONCEPT.md (D12).
 */
export function fileKey(poster: string, base: string, totalSegments: number): string {
  return createHash('sha1').update(`${poster}\n${base}\n${totalSegments}`).digest('hex')
}

/** True when a yEnc name looks like a real filename (it has an extension), not a random token. */
export function looksLikeFilename(name: string): boolean {
  return /\.[A-Za-z0-9]{1,5}$/.test(name) && !/^[0-9a-f]{32,}$/i.test(name)
}

/**
 * Identity of a file known only from its yEnc header (obfuscated posts).
 * The poster is left out: obfuscating posters randomise it per article.
 * - A real filename is stable across the articles of a file, and needed to
 *   tell apart the equal-sized volumes of one archive.
 * - A random, extensionless name can change per article too; the exact
 *   byte size and part count are what stays the same.
 * Collisions are caught by the conflict check in IngestService.
 */
export function weakFileKey(name: string, size: number, totalParts: number): string {
  const identity = looksLikeFilename(name) ? `name\n${name}` : 'shape'
  return createHash('sha1').update(`weak\n${identity}\n${size}\n${totalParts}`).digest('hex')
}

/**
 * Identity of a file by its counters, for uploads that give every article
 * its own random subject (CONCEPT.md D36): poster, file counter `[i/M]`,
 * part count and posting day stay the same across the articles of one file.
 * The day keeps different uploads with the same shape apart; collisions that
 * remain are caught by the conflict check (these files are weak identities).
 * Null when the subject has no file counter.
 */
export function counterFileKey(segment: { poster: string; subject: string; totalParts: number; postedAt?: Date }): string | null {
  const counter = /\[(\d+)\/(\d+)\]/.exec(segment.subject)
  if (!counter || segment.totalParts < 2) return null
  const day = segment.postedAt && !Number.isNaN(segment.postedAt.getTime()) ? segment.postedAt.toISOString().slice(0, 10) : ''
  return createHash('sha1')
    .update(`counter\n${segment.poster}\n${Number(counter[1])}/${Number(counter[2])}\n${segment.totalParts}\n${day}`)
    .digest('hex')
}