1 files changed, 21 insertions, 15 deletions

diff --git a/mines.kt b/mines.kt
index b4d7d77..ae8415d 100644
--- a/mines.kt
+++ b/mines.kt
@@ -1,5 +1,8 @@
 data class Tile(val adjacentMines: Int = 0, val mine: Boolean = false, val masked: Boolean = true)
 
+/**
+ * The Minesweeper "grid", containing instances of [Tile].
+ */
 class Grid(val width: Int, val height: Int, val tiles: Array<Tile>) {
     constructor(width: Int = 8, height: Int = 8, mines: Int = 10)
     : this(width, height, Array<Tile>(width * height) { Tile() }) {
@@ -11,8 +14,7 @@ class Grid(val width: Int, val height: Int, val tiles: Array<Tile>) {
     }
 
     private fun index(x: Int, y: Int) = y * width + x
-    private fun coordinatesValid(x: Int, y: Int) = y >= 0 && y < height && x >= 0 && x < width
-
+    private fun valid(x: Int, y: Int) = y in 0 until height && x in 0 until width
     private fun place(x: Int, y: Int, tile: Tile) {
         tiles[index(x, y)] = tile
     }
@@ -24,7 +26,7 @@ class Grid(val width: Int, val height: Int, val tiles: Array<Tile>) {
      * the range of [0, width), or if the Y coordinate is outside the
      *  range of [0, height).
      */
-    fun tile(x: Int, y: Int) = if (coordinatesValid(x, y)) {
+    operator fun get(x: Int, y: Int) = if (valid(x, y)) {
         tiles[index(x, y)]
     } else {
         throw IllegalArgumentException("Invalid coordinates (${x}, ${y})")
@@ -38,16 +40,20 @@ class Grid(val width: Int, val height: Int, val tiles: Array<Tile>) {
      *  range of [0, height).
      */
     fun placeMine(x: Int, y: Int) {
-        if (!coordinatesValid(x, y)) {
+        if (!valid(x, y)) {
             throw IllegalArgumentException("Invalid coordinates (${x}, ${y})")
         }
 
+        if (this[x, y].mine) {
+            return;
+        }
+
         place(x, y, Tile(mine = true))
 
-        val xMin = if (x - 1 < 0) { x } else { x - 1 }
-        val xMax = if (x + 1 >= width) { x } else { x + 1 }
-        val yMin = if (y - 1 < 0) { y } else { y - 1 }
-        val yMax = if (y + 1 >= height) { y } else { y + 1 }
+        val xMin = (x - 1).coerceAtLeast(0)
+        val xMax = (x + 1).coerceAtMost(width - 1)
+        val yMin = (y - 1).coerceAtLeast(0)
+        val yMax = (y + 1).coerceAtMost(height - 1)
 
         for (y in yMin..yMax) {
             for (x in xMin..xMax) {
@@ -68,18 +74,18 @@ class Grid(val width: Int, val height: Int, val tiles: Array<Tile>) {
      *  range of [0, height).
      */
     fun reveal(x: Int, y: Int) {
-        if (!coordinatesValid(x, y) || !tile(x, y).masked) {
+        if (!valid(x, y) || !this[x, y].masked) {
             return;
         }
 
-        with (tile(x, y)) {
+        with (this[x, y]) {
             place(x, y, copy(masked = false))
 
             if (!mine && adjacentMines == 0) {
-                val xMin = if (x - 1 < 0) { x } else { x - 1 }
-                val xMax = if (x + 1 >= width) { x } else { x + 1 }
-                val yMin = if (y - 1 < 0) { y } else { y - 1 }
-                val yMax = if (y + 1 >= height) { y } else { y + 1 }
+                val xMin = (x - 1).coerceAtLeast(0)
+                val xMax = (x + 1).coerceAtMost(width - 1)
+                val yMin = (y - 1).coerceAtLeast(0)
+                val yMax = (y + 1).coerceAtMost(height - 1)
 
                 for (y in yMin..yMax) {
                     for (x in xMin..xMax) {
@@ -93,7 +99,7 @@ class Grid(val width: Int, val height: Int, val tiles: Array<Tile>) {
     override fun toString(): String = buildString {
         for (y in 0 until height) {
             for (x in 0 until width) {
-                val tile = tile(x, y)
+                val tile = this@Grid[x, y]
                 append(when {
                     tile.masked -> "."
                     tile.mine -> "M"