A basic type ahead

TypeAheadTest.kt

import kotlinx.coroutines.delay
import kotlinx.coroutines.flow.Flow
import kotlinx.coroutines.flow.collect
import kotlinx.coroutines.flow.debounce
import kotlinx.coroutines.flow.filter
import kotlinx.coroutines.flow.flow
import kotlinx.coroutines.flow.transform
import kotlinx.coroutines.flow.transformLatest
import kotlinx.coroutines.runBlocking
import org.junit.Test

class TypeAheadTest {
    private var queryCount = 0
    private suspend fun getResultsAsync(query: String): List<String> {
        println("Query${queryCount++}: $query")
        return if (query == "hell") {
            delay(1000) // just to introduce some unexpected delay
            listOf("hell, hellfire, hell and fury")
        } else if (query == "hello wor") {
            listOf("hello world", "hello world!", "hello worms")
        } else {
            listOf("unknown")
        }
    }

    private val MIN_CHARACHTER_COUNT_FOR_SEARCH = 3
    private suspend fun handleTypeAhead(dataSource: Flow<String>, onChange: (results: List<String>) -> Unit) {

        // if a user is typing quickly wait for a pause before collecting most recent update. Ignore anything less then 3 characters.
        val resultsFromUser = dataSource.debounce(500).filter { it.length > MIN_CHARACHTER_COUNT_FOR_SEARCH }

        // make an api call to get results for each user's query
        // transformLatest will cancel an older api call if a newer arrives first
        // this ensures a user will not see typeahead results for an out of date query
        val apiCalls = resultsFromUser.transformLatest {
            emit(getResultsAsync(it))
        }

        // pass the queries onto the subscriber. ex. the view to show these updates
        apiCalls.collect {
            onChange(it)
        }
    }

    @Test
    fun test1() {
        val typeAheadResults = flow {
            emit("h")
            emit("he")
            emit("hell")
            delay(501)
            emit("hello wor")
        }

        runBlocking {
            handleTypeAhead(typeAheadResults) {
                println("results: $it")
            }
        }
    }
}