delete-collection.kt

/** Deletes all scouts for a team, including their `metrics` subcollection. */
fun Team.deleteAllScouts() {
    ref.collection("scouts").delete() // Kotlin's syntactic sugar
            .addOnSuccessListener { snapshots: List<DocumentSnapshot> ->
                for (snapshot in snapshots) deleteScout(snapshot.id)
            }
}

fun Team.deleteScout(id: String) {
    val scoutDoc = ref.collection("scouts").document(id)
    scoutDoc.delete() // Native document deletion
    scoutDoc.collection("metrics").delete() // Kotlin's syntactic sugar
}

/**
 * Delete all documents in a collection. This does **not** automatically discover and delete
 * sub-collections.
 */
fun CollectionReference.delete(batchSize: Long = 100): Task<List<DocumentSnapshot>> = async {
    val deleted = ArrayList<DocumentSnapshot>()

    var query = orderBy(FieldPath.documentId()).limit(batchSize)
    var latestDeleted = deleteQueryBatch(query)
    deleted += latestDeleted

    while (latestDeleted.size >= batchSize) {
        query = orderBy(FieldPath.documentId()).startAfter(latestDeleted.last()).limit(batchSize)
        latestDeleted = deleteQueryBatch(query)
    }

    deleted as List<DocumentSnapshot>
}

/** Delete all results from a query in a single [WriteBatch]. */
@WorkerThread
private fun deleteQueryBatch(query: Query): List<DocumentSnapshot> = Tasks.await(query.get()).let {
    Tasks.await(firestoreBatch {
        for (snapshot in it) delete(snapshot.reference)
    })
    it.documents
}

inline fun <T> async(crossinline block: () -> T): Task<T> =
        AsyncTaskExecutor.execute(Callable { block() })

object AsyncTaskExecutor : Executor {
    private val service = Executors.newCachedThreadPool()

    fun <TResult> execute(callable: Callable<TResult>): Task<TResult> = Tasks.call(this, callable)

    override fun execute(runnable: Runnable) {
        service.submit(runnable)
    }
}