Kotlin for Java Developers: week 4, Programming Assignment: Board

BoardImpl.kt

package board

import board.Direction.*

private open class SquareBoardImpl(width: Int) : SquareBoard {

  override val width: Int = width

  private val cells: List<List<Cell>> = (1..width).map { row ->
    (1..width).map { Cell(row, it) }
  }

  override fun getCellOrNull(i: Int, j: Int): Cell? =
    cells.getOrNull(i - 1)?.getOrNull(j - 1)

  override fun getCell(i: Int, j: Int): Cell =
    cells[i - 1][j - 1]

  override fun getAllCells(): Collection<Cell> = cells.flatten()

  override fun getRow(i: Int, jRange: IntProgression): List<Cell> =
    jRange.mapNotNull { getCellOrNull(i, it) }

  override fun getColumn(iRange: IntProgression, j: Int): List<Cell> =
    iRange.mapNotNull { getCellOrNull(it, j) }

  override fun Cell.getNeighbour(direction: Direction): Cell? =
    when(direction) {
      UP -> getCellOrNull(i - 1, j)
      RIGHT -> getCellOrNull(i, j + 1)
      DOWN -> getCellOrNull(i + 1, j)
      LEFT -> getCellOrNull(i, j - 1)
    }
}

private class GameBoardImpl<T>(width: Int) : SquareBoardImpl(width), GameBoard<T> {
  private val values: MutableMap<Cell, T> = mutableMapOf()

  override fun get(cell: Cell): T? = values[cell]

  override fun set(cell: Cell, value: T?) {
    if (value != null) values[cell] = value
  }

  override fun filter(predicate: (T?) -> Boolean): Collection<Cell> = getAllCells()
    .associateWith { values[it] }
    .filterValues(predicate)
    .keys

  override fun find(predicate: (T?) -> Boolean): Cell? = getAllCells()
    .map { Pair(it, values[it]) }
    .find { (_, value) -> predicate(value) }
    ?.first

  override fun any(predicate: (T?) -> Boolean): Boolean = getAllCells()
    .map { Pair(it, values[it]) }
    .any { (_, value) -> predicate(value) }

  override fun all(predicate: (T?) -> Boolean): Boolean = getAllCells()
    .map { Pair(it, values[it]) }
    .all { (_, value) -> predicate(value) }
}

fun createSquareBoard(width: Int): SquareBoard = SquareBoardImpl(width)
fun <T> createGameBoard(width: Int): GameBoard<T> = GameBoardImpl(width)