export function loadConfig(environment = process.env) {
  const publicOrigin = required(environment, 'REMORA_WEB_PUBLIC_ORIGIN')
  const apiUpstream = required(environment, 'REMORA_WEB_API_UPSTREAM')
  const oidcAuthority = required(environment, 'REMORA_WEB_OIDC_AUTHORITY')
  return {
    root: environment.REMORA_WEB_ROOT || '/app/dist',
    port: port(environment.REMORA_WEB_PORT || '8080'),
    publicOrigin: new URL(publicOrigin).origin,
    apiUpstream: trailingSlash(new URL(apiUpstream)),
    eventsUpstream: webSocketUrl(
      environment.REMORA_WEB_EVENTS_UPSTREAM ||
        new URL('events', trailingSlash(new URL(apiUpstream))).toString(),
    ),
    oidcAuthority: oidcAuthority.replace(/\/$/, ''),
    oidcClientId: required(environment, 'REMORA_WEB_OIDC_CLIENT_ID'),
    oidcClientSecret: required(environment, 'REMORA_WEB_OIDC_CLIENT_SECRET'),
    oidcScope: environment.REMORA_WEB_OIDC_SCOPE || 'openid profile',
    sessionUrl: required(environment, 'REMORA_WEB_SESSION_URL'),
    sessionNamespace:
      environment.REMORA_WEB_SESSION_NAMESPACE || 'remora:web-session:',
    sessionTtlSeconds: positiveInteger(
      environment.REMORA_WEB_SESSION_TTL_SECONDS || '28800',
      'REMORA_WEB_SESSION_TTL_SECONDS',
    ),
    secureCookie: true,
  }
}

function required(environment, name) {
  const value = environment[name]
  if (value === undefined || value === '')
    throw new Error(`${name} is required`)
  return value
}

function port(value) {
  const parsed = positiveInteger(value, 'REMORA_WEB_PORT')
  if (parsed > 65535) throw new Error('REMORA_WEB_PORT must be a valid port')
  return parsed
}

function positiveInteger(value, name) {
  const parsed = Number(value)
  if (!Number.isSafeInteger(parsed) || parsed < 1)
    throw new Error(`${name} must be a positive integer`)
  return parsed
}

function trailingSlash(url) {
  if (!url.pathname.endsWith('/')) url.pathname += '/'
  return url
}

function webSocketUrl(value) {
  const url = new URL(value)
  if (url.protocol === 'http:') url.protocol = 'ws:'
  else if (url.protocol === 'https:') url.protocol = 'wss:'
  if (url.protocol !== 'ws:' && url.protocol !== 'wss:')
    throw new Error('REMORA_WEB_EVENTS_UPSTREAM must use HTTP or WebSocket')
  return url
}