Coverage Summary for Class: RemoteFlagFetch (com.georgeci.moneysurfer.appconfig.remote)

 package com.georgeci.moneysurfer.appconfig.remote
 
 import co.touchlab.kermit.Logger
 import dev.gitlive.firebase.firestore.DocumentSnapshot
 import dev.gitlive.firebase.firestore.FirebaseFirestore
 import kotlinx.coroutines.CancellationException
 import kotlinx.serialization.builtins.MapSerializer
 import kotlinx.serialization.builtins.nullable
 import kotlinx.serialization.builtins.serializer
 import org.koin.core.annotation.Single
 
 /** Shared by the two halves of this layer — they are one subsystem in the log. */
 internal const val REMOTE_CONFIG_LOG_TAG = "RemoteConfig"
 
 /**
  * One read of the server-owned flag document, reduced to the shape the layer needs.
  *
  * A seam rather than a direct Firestore call inside the source: `FirebaseFirestore` is a final
  * gitlive class with no test double, so without this the filtering and mirroring rules — which are
  * the part with actual decisions in them — could not be tested at all.
  */
 fun interface RemoteFlagDocument {
     suspend fun fetch(): RemoteFlagFetch
 }
 
 /**
  * Why the two cases are distinct: a document that was read and holds nothing must **clear** the
  * mirror, while a document that could not be read must **leave it alone**. Collapsing them into an
  * empty map would drop every flag the moment a device went offline; collapsing them the other way
  * would make a retracted flag stick forever on a device that missed the retraction.
  */
 sealed interface RemoteFlagFetch {
 
     /** The server answered. [values] is empty when the document does not exist. */
     data class Read(val values: Map<String, String>) : RemoteFlagFetch
 
     /** Unreachable or unreadable. Already logged; the mirror keeps what it has. */
     data object Unavailable : RemoteFlagFetch
 }
 
 /**
  * Reads `appConfig/flags` as a free-form map.
  *
  * Free-form in its *names*, not its value types: everything is decoded to `String`, which is the
  * form every `ConfigCodec` already expects. gitlive's decoder stringifies whatever the field holds,
  * so a boolean typed into the Firebase Console arrives as `"true"` and `BooleanConfigCodec` accepts
  * it — the owner does not have to remember to quote flag values. A value no codec can read is still
  * mirrored and surfaces as `LayerValue.Undecodable`, so the debug panel shows what the server
  * actually sent rather than a fallback dressed up as the current value.
  *
  * This is the second reader of the `appConfig` collection and deliberately not the first: the
  * app-version gate keeps its own typed `appConfig/mobile` document and its awaitable, fail-open
  * `refresh()`. See ADR-004 → "Version gate stays as it is".
  */
 @Single(binds = [RemoteFlagDocument::class])
 class FirestoreRemoteFlagDocument(private val firestore: FirebaseFirestore) : RemoteFlagDocument {
 
     private val log = Logger.withTag(REMOTE_CONFIG_LOG_TAG)
 
     @Suppress("TooGenericExceptionCaught") // Any fetch failure must degrade to the mirror, not propagate.
     override suspend fun fetch(): RemoteFlagFetch = try {
         firestore.collection(COLLECTION).document(DOCUMENT).get().toFetch()
     } catch (cancelled: CancellationException) {
         throw cancelled
     } catch (failure: Throwable) {
         // Message, not throwable: `CrashReportingLogWriter` turns any Warn carrying a `Throwable`
         // into a Crashlytics non-fatal, and this branch is the *expected* one — every offline
         // foreground return lands here. Attaching the failure would file one non-fatal per
         // foreground return per offline user and bury real crashes. The breadcrumb is the signal
         // worth keeping; a permanent failure surfaces through `isDegraded` instead.
         log.w { "$COLLECTION/$DOCUMENT unreadable (${failure.message}) — resolving from the mirrored values" }
         RemoteFlagFetch.Unavailable
     }
 
     /**
      * A **missing** document is only an answer when the server said so — and the SDK guarantees
      * that for us, rather than this code having to test for it.
      *
      * `get()` does fall back to Firestore's local cache when the network is unreachable, but it
      * does not hand back an empty snapshot in that case: `DocumentReference` converts
      * `!exists && metadata.isFromCache` into an `UNAVAILABLE` failure ("Failed to get document
      * because the client is offline") on Android, iOS and the desktop JVM alike. So an offline
      * cache miss arrives here as a throw and is caught above as [RemoteFlagFetch.Unavailable], and
      * a snapshot that does reach this function with `exists == false` really is the server saying
      * the document is gone.
      *
      * That distinction is the one this layer turns on: clearing the mirror on a merely-offline
      * device would revert a kill switch to its `default = true` and switch the killed feature back
      * on. It is delivered by the `try`/`catch` above, not by anything in here.
      */
     private fun DocumentSnapshot.toFetch(): RemoteFlagFetch {
         if (!exists) return RemoteFlagFetch.Read(emptyMap())
         // A field the owner cleared to `null` instead of deleting is absent, not the string "null":
         // gitlive decodes every field through `toString()`, so a nullable value serializer is what
         // keeps `null` from being mirrored — and `StringConfigCodec` would happily serve it.
         return RemoteFlagFetch.Read(data(FLAG_MAP).mapNotNull { (name, value) -> value?.let { name to it } }.toMap())
     }
 
     private companion object {
         const val COLLECTION = "appConfig"
         const val DOCUMENT = "flags"
         val FLAG_MAP = MapSerializer(String.serializer(), String.serializer().nullable)
     }
 }