export const LOCAL_DEFAULT_BACKEND_URL = "http://localhost:8000"

export type ConfiguredBackendUrl =
  | { kind: "local" }
  | { kind: "fixed"; url: string }
  | { kind: "same-origin" }

export function configuredBackendUrl(): ConfiguredBackendUrl {
  const raw = process.env.NEXT_PUBLIC_BACKEND_URL
  if (raw === undefined || raw === "local") return { kind: "local" }
  if (raw === "" || raw === "same-origin") return { kind: "same-origin" }
  return { kind: "fixed", url: raw.replace(/\/$/, "") }
}

export function defaultDataSourceMode(): "mock" | "live" {
  if (!isMockDataSourceAvailable()) return "live"
  return process.env.NEXT_PUBLIC_DEFAULT_DATA_SOURCE === "live" ? "live" : "mock"
}

export function isMockDataSourceAvailable(): boolean {
  return process.env.NEXT_PUBLIC_ALLOW_MOCK_DATA !== "false"
}

export function isBackendUrlLocked(): boolean {
  const cfg = configuredBackendUrl()
  return cfg.kind === "same-origin" || cfg.kind === "fixed"
}

function isLoopbackHost(hostname: string): boolean {
  return hostname === "localhost" || hostname === "127.0.0.1"
}

/** Prefer same-origin when the UI is not on loopback — never point the browser at localhost. */
export function resolveStoredBackendUrl(stored: string | null): string {
  const cfg = configuredBackendUrl()
  if (cfg.kind === "fixed") return cfg.url
  if (cfg.kind === "same-origin") {
    if (typeof window !== "undefined") return window.location.origin
    return ""
  }
  if (typeof window !== "undefined" && !isLoopbackHost(window.location.hostname)) {
    return window.location.origin
  }
  const trimmed = stored?.trim().replace(/\/$/, "")
  if (trimmed && /^https?:\/\/(localhost|127\.0\.0\.1)(:\d+)?$/i.test(trimmed)) {
    if (typeof window !== "undefined" && !isLoopbackHost(window.location.hostname)) {
      return window.location.origin
    }
  }
  return trimmed || LOCAL_DEFAULT_BACKEND_URL
}