DiscoveryClient

open class DiscoveryClient(val mapper: ObjectMapper, val template: RestTemplate) {
    private fun <E> List<E>.random(random: java.util.Random): E? = if (size > 0) get(random.nextInt(size)) else null

    fun getUrl(appId: String): String? {
        val endpoint = System.getenv("DISCOVERY_SERVER_ENDPOINT")
        val response = template.get("$endpoint/discovery/apps", "application/json", BasicNameValuePair("appId", appId))
        val instances: List<InstanceInfo> = mapper.readValue(response, object : TypeReference<List<InstanceInfo>>() {})
        return when {
            instances.isEmpty() -> null
            else -> instances.random(Random())!!.url
        }
    }