gistfile1.txt

package katas.kotlin.aaa

import katas.kotlin.shouldEqual
import org.junit.Test

data class Cell(val x: Int, val y: Int)

data class Board(val cells: List<Cell> = emptyList()) {
    fun evolve(): Board {
        val newCells = cells.mapNotNull { cell ->
            val n = neighbours(cell).size
            if (n == 3 || n == 4) cell else null
        }
        val deadNeighbours = cells
            .flatMap { cell -> neighbours(cell) }
            .distinct()
            .filterNot { cells.contains(it) }
        deadNeighbours.mapNotNull { cell ->

        }

        return Board(newCells)
    }

    private fun neighbours(cell: Cell): List<Cell> {
        val shifts = listOf(
            Pair(0, -2),
            Pair(0, 2),
            Pair(-1, -1),
            Pair(-1, 1),
            Pair(1, -1),
            Pair(1, 1)
        )
        return shifts
            .map { shift -> Cell(cell.x + shift.first, cell.y + shift.second) }
            .filter { cells.contains(it) }
    }
}

class HexagonalGameOfLIfe {
    @Test fun `empty board evolves to an empty board`() {
        Board().evolve() shouldEqual Board()
    }

    @Test fun `single cell evolves to an empty board`() {
        Board(cells = listOf(Cell(0, 0))).evolve() shouldEqual Board()
    }

    @Test fun `two cells evolves to an empty board`() {
        Board(cells = listOf(Cell(0, 0), Cell(0, 2))).evolve() shouldEqual Board()
    }

    @Test fun `cell with 2 neighbours evolve to an empty board`() {
        Board(cells = listOf(Cell(0, -2), Cell(0, 0), Cell(0, 2))).evolve() shouldEqual Board()
    }

    @Test fun `cell with 3 or 4 neighbours stays alive`() {
        Board(cells = listOf(
            Cell(0, -2),
            Cell(0, 0),
            Cell(1, -1),
            Cell(1, 1)
        )).evolve() shouldEqual Board(cells = listOf(
            Cell(0, 0),
            Cell(1, -1)
        ))
    }
}