Importing a large file into a local database

The whole operation is one cold flow that emits a small sealed progress type. The caller collects it; nothing else needs to know how the work is split.

sealed interface ImportProgress {
    data object Preparing : ImportProgress
    data class Importing(val processed: Int, val total: Int) : ImportProgress
    data class Success(val result: ImportResult) : ImportProgress
    data class Error(val message: String) : ImportProgress
}

override fun import(json: String, invalidFileMessage: String): Flow<ImportProgress> = flow {
    emit(ImportProgress.Preparing)
    …
}.flowOn(Dispatchers.IO)