/**
 * Best-effort Hyperdrive → statvfs-like counters for `/proc/bare_os_resources` and `df`.
 * Hyperdrive versions differ; probes are defensive.
 */
import b4a from 'b4a'

/**
 * @param {unknown} drive
 * @returns {{ f_bsize: number, f_frsize: number, f_blocks: number, f_bfree: number, f_bavail: number, f_files: number | null, f_ffree: number | null, f_namemax: number, fsidPrefixHex?: string } | null}
 */
export function bareOsStatvfsFromHyperdrive(drive) {
  if (!drive || typeof drive !== 'object') return null
  const bsize = 4096
  /** @type {number} */
  let usedBytes = 0
  try {
    const c = /** @type {{ byteLength?: number, tree?: { byteLength?: number, length?: number } }} */ (
      drive
    ).core
    if (c && typeof c.byteLength === 'number') usedBytes = c.byteLength
    else if (c && c.tree && typeof c.tree.byteLength === 'number')
      usedBytes = c.tree.byteLength
    else if (c && c.tree && typeof c.tree.length === 'number')
      usedBytes = Math.max(usedBytes, (c.tree.length | 0) * 256)
  } catch {
    return null
  }
  if (!Number.isFinite(usedBytes) || usedBytes < 0) return null
  const usedBlocks = Math.max(1, Math.ceil(usedBytes / bsize))
  const headroom = Math.max(4096, usedBlocks)
  const blocks = usedBlocks + headroom
  const bfree = Math.max(0, blocks - usedBlocks)
  let fsidPrefixHex
  try {
    const k = /** @type {{ key?: Uint8Array }} */ (drive).key
    if (k && k.byteLength) fsidPrefixHex = b4a.toString(k, 'hex').slice(0, 16)
  } catch {
    /* optional */
  }
  return {
    f_bsize: bsize,
    f_frsize: bsize,
    f_blocks: blocks,
    f_bfree: bfree,
    f_bavail: bfree,
    f_files: null,
    f_ffree: null,
    f_namemax: 255,
    fsidPrefixHex
  }
}