App.kt

package chapter15

fun main() {
    Game.play()
}

Game.kt

package chapter15

import java.lang.Exception
import java.lang.IllegalStateException

object Game {
    private var running = true
    private val player = Player("Madrigal")
    private var currentRoom: Room = TownSquare()

    private var worldMap = listOf(
            listOf(currentRoom, Room("Tavern"), Room("Back Room")),
            listOf(Room("Long Corridor"), Room("Generic Room"))
    )

    init {
        println("Welcome, adventurer.")
        player.castFireball()
    }

    fun play() {
        while (running) {
            print("> Enter you command: ")
            println(GameInput(readLine()).processCommand())
        }
    }

    private fun move(directionInput: String) =
            try {
                val direction = Direction.valueOf(directionInput.toUpperCase())
                val newPosition = direction.updateCoordinate(player.currentPosition)
                if (!newPosition.isInBounds) {
                    throw IllegalStateException("$direction is out of bounds.")
                }

                val newRoom = worldMap[newPosition.y][newPosition.x]
                player.currentPosition = newPosition
                currentRoom = newRoom
                "OK, you move $direction to the ${newRoom.name}.\n${newRoom.load()}"
            } catch (e: Exception) {
                "Invalid direction: $directionInput."
            }

    private fun map(): String {
        var output = ""

        for (row in worldMap) {
            for (column in row) {
                output += if (column.name == currentRoom.name) {
                    "O"
                } else {
                    "X"
                }
            }
            output += "\n"
        }

        return output
    }

    private fun ring(): String {
        return currentRoom.ringBell()
    }

    private fun quit(): String {
        running = false
        return "Bye, adventurer"
    }

    private fun printPlayerStatus(player: Player) {
        println("(Aura:  ${player.auraColor()}) " +
                "(Blessed: ${if (player.isBlessed) "YES" else "NO"}")
        println("${player.name} ${player.formatHealthStatus()}")
    }

    private class GameInput(arg: String?) {
        private val input = arg ?: ""
        val command = input.split(" ")[0]
        val argument = input.split(" ").getOrElse(1, { "" })

        fun processCommand() = when(command.toLowerCase()) {
            "move" -> move(argument)
            "map" -> map()
            "ring" -> ring()
            "quit" -> quit()
            else -> commandNotFound()
        }
        private fun commandNotFound() = "I'm not quite sure what you're trying to do!"
    }
}

Navigation.kt

package chapter15

enum class Direction(private val coordinate: Coordinate) {
    NORTH(Coordinate(0, -1)),
    EAST(Coordinate(1, 0)),
    SOUTH(Coordinate(0, 1)),
    WEST(Coordinate(-1, 0));

    fun updateCoordinate(playerCoordinate: Coordinate) =
            Coordinate(playerCoordinate.x + coordinate.x, playerCoordinate.y + coordinate.y)
}

data class Coordinate(val x: Int, val y: Int) {
    val isInBounds = x >= 0 && y >= 0

    operator fun plus(other: Coordinate) = Coordinate(x + other.x, y + other.y)
}

Player.kt

package chapter15

class Player(_name: String,
             var healthPoints: Int = 100,
             val isBlessed: Boolean,
             private val isImmortal: Boolean) {

    var name = _name
        get() = "${field.capitalize()} of $hometown"
        private set(value) {
            field = value.trim()
        }

    val hometown by lazy { selectHometown() }
    var currentPosition = Coordinate(0, 0)

    init {
        require(healthPoints > 0, { "healthPoints must be greater than zero." })
        require(name.isNotBlank(), { "Player must have a namel" })
    }

    constructor(name: String): this(name, isBlessed = true, isImmortal = false) {
        if (name.toLowerCase() == "kar") healthPoints = 40
    }

    private fun selectHometown(): String {
        return listOf(
                "Taipei",
                "Taichung",
                "Kaohsiung",
                "Taitung"
        ).shuffled().first()
    }

    fun castFireball(numFirballs: Int = 2) {
        //println("A glass of Fireball springs into existence. (x$numFirballs)")
    }

    fun formatHealthStatus(): String {
        return "Health Status: ..."
    }

    fun auraColor(): String {
        return "Aura Color: ..."
    }
}

Room.kt

package chapter15

open class Room(val name: String) {
    protected open val dangerLevel = 5
    protected open val bellSound = "DING"

    fun description() = "Room: $name\nDanger level: $dangerLevel"

    open fun load() = "Nothing much to see here..."

    open fun ringBell() = "$bellSound from $name"
}

TownSquare.kt

package chapter15

open class TownSquare : Room("Town Square") {
    override val dangerLevel = super.dangerLevel - 3
    override val bellSound = "GWONG"

    override fun load() = "The villagers rally and cheer as you enter!\n${ringBell()}"

    override fun ringBell() = "The bell tower announce your arrival. $bellSound"
}