Implement posting thumbs-up count to firestore

data/firestore/src/commonMain/kotlin/io/github/droidkaigi/confsched2020/data/firestore/Firestore.kt

@@ -6,4 +6,5 @@ import kotlinx.coroutines.flow.Flow
 interface Firestore {
     fun getFavoriteSessionIds(): Flow<List<String>>
     suspend fun toggleFavorite(sessionId: SessionId)
+    fun thumbsUp(sessionId: SessionId): Flow<Int>
 }

data/firestore/src/main/java/io/github/droidkaigi/confsched2020/data/firestore/internal/FirestoreImpl.kt

@@ -1,15 +1,20 @@
 package io.github.droidkaigi.confsched2020.data.firestore.internal
 
+import com.google.android.gms.tasks.Task
+import com.google.android.gms.tasks.Tasks
 import com.google.firebase.auth.FirebaseAuth
 import com.google.firebase.firestore.CollectionReference
 import com.google.firebase.firestore.DocumentReference
 import com.google.firebase.firestore.DocumentSnapshot
+import com.google.firebase.firestore.FieldValue
 import com.google.firebase.firestore.FirebaseFirestore
 import com.google.firebase.firestore.Query
 import com.google.firebase.firestore.QuerySnapshot
 import com.google.firebase.firestore.Source
 import io.github.droidkaigi.confsched2020.data.firestore.Firestore
 import io.github.droidkaigi.confsched2020.model.SessionId
+import io.github.droidkaigi.confsched2020.model.Shard
+import io.github.droidkaigi.confsched2020.model.ThumbsUpCounter
 import javax.inject.Inject
 import kotlinx.coroutines.channels.awaitClose
 import kotlinx.coroutines.flow.Flow
@@ -20,8 +25,13 @@ import kotlinx.coroutines.flow.mapLatest
 import kotlinx.coroutines.tasks.await
 import timber.log.Timber
 import timber.log.debug
+import kotlin.math.floor
+import kotlin.math.sin
 
 internal class FirestoreImpl @Inject constructor() : Firestore {
+    companion object {
+        const val NUM_SHARDS = 10
+    }
 
     override fun getFavoriteSessionIds(): Flow<List<String>> {
         val setupFavorites = flow {
@@ -63,6 +73,15 @@ internal class FirestoreImpl @Inject constructor() : Firestore {
         Timber.debug { "toggleFavorite: end" }
     }
 
+    override fun thumbsUp(sessionId: SessionId): Flow<Int> {
+        return flow {
+            signInIfNeeded()
+            val counterRef = createThumbsUpCounterIfNeeded(sessionId = sessionId, numShards = NUM_SHARDS)
+            incrementThumbsUpCount(counterRef)
+            emit(getThumbsUpCount(counterRef))
+        }
+    }
+
     private fun getFavoritesRef(): CollectionReference {
         val firebaseAuth = FirebaseAuth.getInstance()
         val firebaseUserId = firebaseAuth.currentUser?.uid ?: throw RuntimeException(
@@ -83,6 +102,62 @@ internal class FirestoreImpl @Inject constructor() : Firestore {
         firebaseAuth.signInAnonymously().await()
         Timber.debug { "signInIfNeeded end" }
     }
+
+    private suspend fun createThumbsUpCounterIfNeeded(sessionId: SessionId, numShards: Int): DocumentReference {
+        val firebaseAuth = FirebaseAuth.getInstance()
+        val firebaseUserId = firebaseAuth.currentUser?.uid ?: throw RuntimeException(
+            "RuntimeException"
+        )
+        val counterDocumentRef = FirebaseFirestore
+            .getInstance()
+            .collection("confsched/2020/sessions/$sessionId/thumbsup_counters")
+            .document(firebaseUserId)
+
+        if (counterDocumentRef.fastGet().exists()) {
+            Timber.debug { "createThumbsUpCounterIfNeeded counter already exists" }
+            return counterDocumentRef
+        }
+
+        counterDocumentRef.set(ThumbsUpCounter(numShards))
+            .continueWithTask { task ->
+                if (!task.isSuccessful) {
+                    throw task.exception!!
+                }
+
+                val tasks = arrayListOf<Task<Void>>()
+
+                // Initialize each shard with count=0
+                for (i in 0 until numShards) {
+                    val makeShard = counterDocumentRef.collection("shards")
+                        .document(i.toString())
+                        .set(Shard(count = 0))
+
+                    tasks.add(makeShard)
+                }
+
+                Tasks.whenAll(tasks)
+            }.await()
+
+        Timber.debug { "createThumbsUpCounterIfNeeded creating counter completed" }
+        return counterDocumentRef
+    }
+
+    private fun incrementThumbsUpCount(counterRef: DocumentReference) {
+        val shardId = floor(Math.random() * NUM_SHARDS).toInt()
+        counterRef.collection("shards")
+            .document(shardId.toString())
+            .update("count", FieldValue.increment(1))
+    }
+
+    private suspend fun getThumbsUpCount(counterRef: DocumentReference): Int {
+        val shards = counterRef.collection("shards").fastGet()
+        var count = 0
+        shards.forEach { snap ->
+            val shard = snap.toObject(Shard::class.java)
+            count += shard.count
+        }
+        return count
+    }
 }
 
 private suspend fun DocumentReference.fastGet(): DocumentSnapshot {

model/src/commonMain/kotlin/io/github/droidkaigi/confsched2020/model/Shard.kt

@@ -0,0 +1,3 @@
+package io.github.droidkaigi.confsched2020.model
+
+data class Shard(val count: Int)

model/src/commonMain/kotlin/io/github/droidkaigi/confsched2020/model/ThumbsUpCounter.kt

@@ -0,0 +1,3 @@
+package io.github.droidkaigi.confsched2020.model
+
+data class ThumbsUpCounter(val numShards: Int)