Game.kt

package me.tabak.jacob.war

class Game(private val deck1: Deck, private val deck2: Deck) {
    fun play() : Int {
        println("Starting game!")
        printDecks()
        var winner = 0
        while (deck1.isNotEmpty() && deck2.isNotEmpty()) {
            winner = battle()
        }
        return winner
    }

    private fun battle(army1: List<Int> = ArrayList(), army2: List<Int> = ArrayList(), depth: Int = 0) : Int {
        return if (deck1.isEmpty() && deck2.isEmpty()) {
            0
        } else if (deck1.isEmpty() || deck2.isEmpty()) {
            if (deck1.isNotEmpty()) 1 else 2
        } else {
            val card1 = deck1.poll()
            val card2 = deck2.poll()
            val winner = when {
                card1 > card2 -> 1
                card1 < card2 -> 2
                else -> war(depth + 1)
            }
            if (winner != 0) {
                claim(winner, army1, army2, card1, card2)
            }
            return winner
        }
    }

    private fun war(depth: Int = 0) : Int {
        println("War!")
        val army1 = ArrayList<Int>()
        val army2 = ArrayList<Int>()

        for (i in 1..3) {
            if (deck1.size > 1 && deck2.size > 1) {
                if (deck1.isEmpty() || deck2.isEmpty()) {
                    return if (deck1.isNotEmpty()) 1 else 2
                } else {
                    army1.add(deck1.poll())
                    army2.add(deck2.poll())
                }
            }
        }

        return battle(army1, army2, depth)
    }

    private fun claim(winner: Int, army1: List<Int>, army2: List<Int>, card1: Int, card2: Int = 0) {
        val winningDeck = if (winner == 1) deck1 else deck2
        val (winningArmy, losingArmy) = if (winner == 1) army1 to army2 else army2 to army1
        val (winningCard, losingCard) = if (winner == 1) card1 to card2 else card2 to card1
        val spoils = ArrayList<Int>()
        winningArmy.forEach { spoils.add(it) }
        spoils.add(winningCard)
        losingArmy.forEach { spoils.add(it) }
        spoils.add(losingCard)
        spoils.forEach { winningDeck.offer(it) }
        println("Deck$winner won $spoils")
        printDecks()
    }

    private fun printDecks() {
        println("""Deck1: $deck1
            |Deck2: $deck2
            """.trimMargin())
    }
}