import type { AggregatedFile } from '../files/index.js'
import type { Fragment } from './range_indexer.js'
import type { EdgeSegment, FileMeta } from './scan.js'

/**
 * The fragments of one file from neighbouring ranges, put together
 * (REBUILD.md, fragments): the complete file when every part from 1 to its
 * total is there (the first article seen of a part wins), else null.
 */
export function mergeFragments(fragments: Fragment[]): AggregatedFile<EdgeSegment> | null {
  if (fragments.length === 0) return null
  const first = fragments[0]
  const meta: FileMeta = {
    fileKey: first.fileKey,
    name: first.name,
    poster: first.poster,
    subject: first.subject,
    totalParts: first.totalParts,
    groups: first.groups,
    release: first.release ? { ...first.release, source: first.release.source as any } : null,
  }
  const parts = new Map<number, EdgeSegment>()
  for (const fragment of fragments) {
    const postedAt = fragment.postedAt ?? Number.NaN
    for (const [number, messageId, bytes, articleNumber] of fragment.segments) {
      const known = parts.get(number)
      if (!known || articleNumber < known.articleNumber) {
        parts.set(number, { fileKey: meta.fileKey, number, totalParts: meta.totalParts, messageId, bytes, articleNumber, postedAt, file: meta })
      }
    }
  }
  if (parts.size < meta.totalParts) return null
  for (let n = 1; n <= meta.totalParts; n++) if (!parts.has(n)) return null
  return { fileKey: meta.fileKey, segments: [...parts.values()].sort((a, b) => a.number - b.number) }
}