// config.ts — reads OIDC configuration injected by the Go server into
// window.__LETHE_CONFIG__ (IF1). The injected JSON uses snake_case field names
// (Go struct json tags); this module converts to camelCase for ergonomic use
// throughout the SPA.

export interface LetheConfig {
  issuer: string
  clientId: string
}

// Raw shape as injected by the Go server (json tags: issuer, client_id).
interface RawLetheConfig {
  issuer: string
  client_id: string
}

declare global {
  interface Window {
    __LETHE_CONFIG__?: RawLetheConfig
  }
}

/**
 * Read the OIDC configuration from window.__LETHE_CONFIG__.
 *
 * Throws Error('lethe config missing') if the property is absent — fail-fast
 * per GPC6. The caller (auth provider mount) should catch this and render an
 * "auth-config missing" error card rather than swallowing the exception.
 */
export function readConfig(): LetheConfig {
  const raw = window.__LETHE_CONFIG__
  if (raw == null) {
    throw new Error('lethe config missing')
  }
  return {
    issuer:   raw.issuer,
    clientId: raw.client_id,
  }
}