function isFirstPageParamValue(raw: string): boolean {
  const normalized = raw.trim()
  if (!normalized) {
    return false
  }
  if (/^\+?0*1(?:\.0+)?$/.test(normalized)) {
    return true
  }
  const parsed = Number(normalized)
  return Number.isFinite(parsed) && parsed === 1
}

export function buildPublicCanonicalUrl(siteUrlRaw: unknown, currentFullPath: unknown): string | null {
  if (typeof siteUrlRaw !== 'string') {
    return null
  }
  const siteUrl = siteUrlRaw.trim()
  if (!siteUrl) {
    return null
  }
  try {
    const base = new URL(siteUrl)
    const path = typeof currentFullPath === 'string' && currentFullPath.trim()
      ? currentFullPath.split('#', 1)[0]!
      : '/'
    const canonical = new URL(path, `${base.origin}/`)
    const pageValues = canonical.searchParams.getAll('page')
    if (pageValues.length > 0 && pageValues.every(isFirstPageParamValue)) {
      canonical.searchParams.delete('page')
    }
    return canonical.href
  }
  catch {
    return null
  }
}