Configuration Over Code

// config.ts: the country config as a typed, validated, versioned object with accessors; loaded per tenant; never read ad hoc
import { z } from 'zod'
export const CountryConfig = z.object({
  country: z.enum(['NG', 'KE', 'GH', 'EG']), version: z.string(),
  currency: z.object({ code: z.string().length(3), exponent: z.number().int().min(0).max(8) }),
  locales: z.object({ default: z.string(), supported: z.array(z.string()).min(1) }),
  identity: z.object({ provider: z.enum(['smile', 'youverify', 'onfido']), documents: z.array(z.string()).min(1), tiers: z.array(Tier) }),
  rails: z.object({ transfer: Rail.optional(), card: Rail.optional(), mobileMoney: Rail.optional() }),   // optional: a missing rail renders "unavailable"
  rules: z.string(),                                                                                  // the rule set id; the rules themselves live in the engine
  features: z.record(z.boolean()),                                                                    // licence facts; experiments and ramps are flags, not here
  legal: z.object({ entity: z.string(), disclosures: z.array(z.string()) }),
}).strict()                                                                                           // an unknown key fails: no smuggling logic in
export type CountryConfig = z.infer<typeof CountryConfig>

let current: CountryConfig | null = null
export async function loadConfig(tenant: string, region: Region) {
  const res = await fetch(`${region.api}/config/${tenant}`, { headers: { 'If-None-Match': etagFor(tenant) ?? '' } })
  const json = res.status === 304 ? cached(tenant) : await res.json()
  const parsed = CountryConfig.safeParse(json)
  if (!parsed.success) throw new ConfigInvalid(tenant, parsed.error)     // a designed load-time state, with the schema version and the tenant; never a crash in a component
  current = parsed.data; telemetry.setDimension('configVersion', parsed.data.version); return parsed.data
}
export const config = {                                                   // accessors: a missing key is a type error here, not an undefined in Ghana
  get currency() { return must().currency },
  rail(kind: keyof CountryConfig['rails']) { return must().rails[kind] ?? null },   // null → the UI's "unavailable in your country" state
  feature(name: string) { return must().features[name] ?? false },
}
const must = () => { if (!current) throw new Error('config not loaded'); return current }