Kotlin Feature Flags

3. Evaluate flags

import kotlinx.coroutines.*
import okhttp3.*
import okhttp3.MediaType.Companion.toMediaType
import okhttp3.RequestBody.Companion.toRequestBody
import org.json.JSONObject

object FlagBit {
    private val client = OkHttpClient()
    private val cache = mutableMapOf<String, Boolean>()
    private val sdkKey = BuildConfig.FLAGBIT_SDK_KEY

    suspend fun isEnabled(flagKey: String, context: Map<String, String> = emptyMap()): Boolean {
        val cacheKey = "$flagKey:${context.hashCode()}"
        cache[cacheKey]?.let { return it }

        return withContext(Dispatchers.IO) {
            try {
                val body = JSONObject().apply {
                    put("flag_key", flagKey)
                    put("context", JSONObject(context))
                }.toString()

                val request = Request.Builder()
                    .url("https://flagbit.anethoth.com/api/v1/evaluate")
                    .addHeader("X-SDK-Key", sdkKey)
                    .post(body.toRequestBody("application/json".toMediaType()))
                    .build()

                val response = client.newCall(request).execute()
                val value = JSONObject(response.body!!.string()).getBoolean("value")
                cache[cacheKey] = value
                value
            } catch (e: Exception) {
                false
            }
        }
    }
}

// Jetpack Compose usage
@Composable
fun HomeScreen() {
    var showNewLayout by remember { mutableStateOf(false) }

    LaunchedEffect(Unit) {
        showNewLayout = FlagBit.isEnabled("new-home",
            context = mapOf("user_id" to userId, "platform" to "android"))
    }

    if (showNewLayout) {
        NewHomeLayout()
    } else {
        ClassicHomeLayout()
    }
}

// ViewModel pattern
class DashboardViewModel : ViewModel() {
    private val _flags = MutableStateFlow<Map<String, Boolean>>(emptyMap())
    val flags: StateFlow<Map<String, Boolean>> = _flags

    init {
        viewModelScope.launch {
            val newDash = FlagBit.isEnabled("new-dashboard")
            val darkMode = FlagBit.isEnabled("force-dark-mode")
            _flags.value = mapOf("new-dashboard" to newDash, "force-dark-mode" to darkMode)
        }
    }

    fun isEnabled(key: String) = flags.value[key] ?: false
}