const INVALID_SUBDOMAINS = new Set([
    '0.0.0.0',
    'www',
    'api',
    'admin',
    'test',
    'dev',
    'development',
    'staging',
    'production',
    'localhost',
])

const DEFAULT_TENANT = 'sistema'

export function tenantFromHost(host: string | undefined | null): string {
    if (!host) return DEFAULT_TENANT
    const sub = host.split(':')[0]?.split('.')[0]?.toLowerCase()
    if (!sub || sub.length <= 1) return DEFAULT_TENANT
    if (INVALID_SUBDOMAINS.has(sub)) return DEFAULT_TENANT
    if (!/^[a-z0-9-]+$/.test(sub)) return DEFAULT_TENANT
    return sub
}

/**
 * Resolve o tenant atual — isomorfo (server e client).
 * No server, prefira passar o host via `tenantFromHost(useRequestHeaders(['host']).host)`.
 */
export function getClientTenant(): string {
    if (typeof window === 'undefined') return DEFAULT_TENANT
    return tenantFromHost(window.location.host)
}