from datetime import datetime, timezone

def iso_stamp_filename(prefix: str, ext: str) -> str:
  """Generate timestamped filename, e.g. pasted-2025-10-23T121212Z.png"""
  ts = datetime.now(timezone.utc).isoformat()
  ts = ts.replace(":", "").split(".")[0]
  if ts.endswith("+00:00"):
    ts = ts.replace("+00:00", "Z")
  return f"{prefix}-{ts}.{ext}"

def format_size(num_bytes: int) -> str:
  """Return a human-readable file size (e.g., '2.3 MB', '10 Bytes')."""
  if num_bytes < 1024:
    return f"{num_bytes} Byte{'s' if num_bytes != 1 else ''}"

  units = ["KB", "MB", "GB", "TB", "PB", "EB"]
  size = float(num_bytes)
  for unit in units:
    size /= 1024.0
    if size < 1024.0 or unit == units[-1]:
      # 1 decimal place; drop trailing .0 (optional)
      val = f"{size:.1f}"
      if val.endswith(".0"):
        val = val[:-2]
      return f"{val} {unit}"
  return f"{num_bytes} Bytes"  # fallback