import { randomUUID } from 'node:crypto'
import { existsSync, renameSync, rmSync, statSync } from 'node:fs'

/** A uniquely named sibling of `entryDir`, so concurrent publishers never share a staging tree. */
export function sharedTreeStagingPath(entryDir, uuid = randomUUID) {
  return `${entryDir}.staging-${process.pid}-${uuid()}`
}

// Publish validated sibling staging via atomic rename; usable shared entry never changes and readers never see partial tree.
// Quarantine only the judged-bad tree; restore on failed swap or if sibling published a good one during probe. Recheck immediately before rename; return whether this call published.
export function publishSharedTree(stagingDir, entryDir, options) {
  const { isUsable } = options
  const uuid = options.uuid ?? randomUUID
  const rename = options.rename ?? renameSync
  let quarantinePath = null
  if (existsSync(entryDir)) {
    const judged = treeIdentity(entryDir)
    if (isUsable(entryDir)) {
      rmSync(stagingDir, { recursive: true, force: true })
      return false
    }
    // Why: the probe takes long enough for a sibling to publish; don't even briefly move theirs.
    if (judged === null || treeIdentity(entryDir) !== judged) {
      rmSync(stagingDir, { recursive: true, force: true })
      return false
    }
    quarantinePath = `${entryDir}.unusable-${process.pid}-${uuid()}`
    try {
      renameSync(entryDir, quarantinePath)
    } catch {
      rmSync(stagingDir, { recursive: true, force: true })
      return false // Another publisher is already replacing it, or (Windows) it is loaded.
    }
    if (judged === null || treeIdentity(quarantinePath) !== judged) {
      rmSync(stagingDir, { recursive: true, force: true })
      try {
        renameSync(quarantinePath, entryDir)
      } catch {
        rmSync(quarantinePath, { recursive: true, force: true }) // A third publisher refilled it.
      }
      return false
    }
  }

  try {
    rename(stagingDir, entryDir)
  } catch {
    rmSync(stagingDir, { recursive: true, force: true })
    if (quarantinePath !== null) {
      try {
        renameSync(quarantinePath, entryDir)
        return false
      } catch {
        rmSync(quarantinePath, { recursive: true, force: true })
      }
    }
    return false
  }

  if (quarantinePath !== null) {
    rmSync(quarantinePath, { recursive: true, force: true })
  }
  return true
}

function treeIdentity(dir) {
  try {
    const { dev, ino } = statSync(dir, { bigint: true })
    return `${dev}:${ino}`
  } catch {
    return null
  }
}