Reactive Hangman - https://forums.bigbears.io/t/hangman-the-series-2-reactive-hangman/391

Hangman.kt

package io.bigbear.judrummer

import kotlinx.coroutines.*
import kotlinx.coroutines.channels.*

fun CoroutineScope.hangman(secretWord: String, letterStream: ReceiveChannel<Char>) = produce {
    var result = Result(
            secretWordLength = secretWord.length,
            knownSecretWord = List(secretWord.length) { '_' }.joinToString("")
    )
    val secretWordIndex = secretWord.withIndex()
    send(result)

    for (letter in letterStream) {
        val containIndexs = secretWordIndex.filter { it.value == letter }.map { it.index }
        val lifeLeft = if (containIndexs.isEmpty()) result.lifeLeft - 1 else result.lifeLeft
        val knownSecretWord = result.knownSecretWord.mapIndexed { index, char -> if (containIndexs.contains(index)) letter else char }.joinToString("")
        val status = if (knownSecretWord == secretWord) Status.WON else if (lifeLeft == 0) Status.LOSE else Status.IN_PROGRESS

        result = result.copy(
                status = status,
                selectedLetter = result.selectedLetter.toMutableList().apply { add(letter) },
                lifeLeft = lifeLeft,
                knownSecretWord = knownSecretWord)

        send(result)

        if (result.status != Status.IN_PROGRESS) close()
    }
    close()
}

enum class Status {
    IN_PROGRESS,
    WON,
    LOSE
}

data class Result(
        val status: Status = Status.IN_PROGRESS,
        val selectedLetter: List<Char> = emptyList(),
        val lifeLeft: Int = 7,
        val secretWordLength: Int = 0,
        val knownSecretWord: String = ""
)

HangmantTest.kt

package io.bigbear.judrummer

import kotlinx.coroutines.channels.*
import kotlinx.coroutines.runBlocking
import org.junit.*

class HangManTest {

    @Test
    fun testA() {
        val testList = listOf(
                'b' to Result(
                        status = Status.IN_PROGRESS,
                        selectedLetter = listOf('b'),
                        lifeLeft = 7,
                        secretWordLength = 7,
                        knownSecretWord = "b__b___"),
                'o' to Result(
                        status = Status.IN_PROGRESS,
                        selectedLetter = listOf('b', 'o'),
                        lifeLeft = 6,
                        secretWordLength = 7,
                        knownSecretWord = "b__b___"),
                'i' to Result(
                        status = Status.IN_PROGRESS,
                        selectedLetter = listOf('b', 'o', 'i'),
                        lifeLeft = 6,
                        secretWordLength = 7,
                        knownSecretWord = "bi_b___"),
                'g' to Result(
                        status = Status.IN_PROGRESS,
                        selectedLetter = listOf('b', 'o', 'i', 'g'),
                        lifeLeft = 6,
                        secretWordLength = 7,
                        knownSecretWord = "bigb___"),
                'a' to Result(
                        status = Status.IN_PROGRESS,
                        selectedLetter = listOf('b', 'o', 'i', 'g', 'a'),
                        lifeLeft = 6,
                        secretWordLength = 7,
                        knownSecretWord = "bigb_a_"),
                'e' to Result(
                        status = Status.IN_PROGRESS,
                        selectedLetter = listOf('b', 'o', 'i', 'g', 'a', 'e'),
                        lifeLeft = 6,
                        secretWordLength = 7,
                        knownSecretWord = "bigbea_"),
                'y' to Result(
                        status = Status.IN_PROGRESS,
                        selectedLetter = listOf('b', 'o', 'i', 'g', 'a', 'e', 'y'),
                        lifeLeft = 5,
                        secretWordLength = 7,
                        knownSecretWord = "bigbea_"
                ),
                'r' to Result(
                        status = Status.WON,
                        selectedLetter = listOf('b', 'o', 'i', 'g', 'a', 'e', 'y', 'r'),
                        lifeLeft = 5,
                        secretWordLength = 7,
                        knownSecretWord = "bigbear"
                )
        )
        runHangmanTest("bigbear", testList)
    }

    @Test
    fun testB() {
        val testList = listOf(
                'b' to Result(
                        status = Status.IN_PROGRESS,
                        selectedLetter = listOf('b'),
                        lifeLeft = 7,
                        secretWordLength = 7,
                        knownSecretWord = "b__b___"),
                'o' to Result(
                        status = Status.IN_PROGRESS,
                        selectedLetter = listOf('b', 'o'),
                        lifeLeft = 6,
                        secretWordLength = 7,
                        knownSecretWord = "b__b___"),
                'a' to Result(
                        status = Status.IN_PROGRESS,
                        selectedLetter = listOf('b', 'o', 'a'),
                        lifeLeft = 6,
                        secretWordLength = 7,
                        knownSecretWord = "b__b_a_"),
                'e' to Result(
                        status = Status.IN_PROGRESS,
                        selectedLetter = listOf('b', 'o', 'a', 'e'),
                        lifeLeft = 6,
                        secretWordLength = 7,
                        knownSecretWord = "b__bea_"),
                'n' to Result(
                        status = Status.IN_PROGRESS,
                        selectedLetter = listOf('b', 'o', 'a', 'e', 'n'),
                        lifeLeft = 5,
                        secretWordLength = 7,
                        knownSecretWord = "b__bea_"),
                'u' to Result(
                        status = Status.IN_PROGRESS,
                        selectedLetter = listOf('b', 'o', 'a', 'e', 'n', 'u'),
                        lifeLeft = 4,
                        secretWordLength = 7,
                        knownSecretWord = "b__bea_"),
                't' to Result(
                        status = Status.IN_PROGRESS,
                        selectedLetter = listOf('b', 'o', 'a', 'e', 'n', 'u', 't'),
                        lifeLeft = 3,
                        secretWordLength = 7,
                        knownSecretWord = "b__bea_"),
                'z' to Result(
                        status = Status.IN_PROGRESS,
                        selectedLetter = listOf('b', 'o', 'a', 'e', 'n', 'u', 't', 'z'),
                        lifeLeft = 2,
                        secretWordLength = 7,
                        knownSecretWord = "b__bea_"),
                'x' to Result(
                        status = Status.IN_PROGRESS,
                        selectedLetter = listOf('b', 'o', 'a', 'e', 'n', 'u', 't', 'z', 'x'),
                        lifeLeft = 1,
                        secretWordLength = 7,
                        knownSecretWord = "b__bea_"),
                'v' to Result(
                        status = Status.LOSE,
                        selectedLetter = listOf('b', 'o', 'a', 'e', 'n', 'u', 't', 'z', 'x', 'v'),
                        lifeLeft = 0,
                        secretWordLength = 7,
                        knownSecretWord = "b__bea_"
                )
        )
        runHangmanTest("bigbear", testList)
    }

    fun runHangmanTest(secretWord: String, testList: List<Pair<Char, Result>>) = runBlocking<Unit> {
        val inputChannel = Channel<Char>()
        val resultChannel = hangman(secretWord, inputChannel)
        resultChannel.receive() shouldEqual Result(
                status = Status.IN_PROGRESS,
                selectedLetter = emptyList(),
                lifeLeft = 7,
                secretWordLength = 7,
                knownSecretWord = "_______"
        )

        testList.forEach { (input, result) ->
            inputChannel.send(input)
            resultChannel.receive() shouldEqual result
        }

        inputChannel.cancel()
    }
}

infix fun Any?.shouldEqual(other: Any?) = Assert.assertEquals(other, this)