1 files changed, 23 insertions, 1 deletions
diff --git a/app/src/main/java/space/jakob/mines/Grid.kt b/app/src/main/java/space/jakob/mines/Grid.kt
index 2eec411..963f8cb 100644
--- a/app/src/main/java/space/jakob/mines/Grid.kt
+++ b/app/src/main/java/space/jakob/mines/Grid.kt
@@ -14,7 +14,12 @@ package space.jakob.mines
 
 import java.util.Random
 
-data class Tile(val adjacentMines: Int = 0, val mine: Boolean = false, val masked: Boolean = true)
+data class Tile(
+    val adjacentMines: Int = 0,
+    val mine: Boolean = false,
+    val masked: Boolean = true,
+    val flagged: Boolean = false
+)
 
 /**
  * The Minesweeper "grid", containing instances of [Tile].
@@ -118,6 +123,23 @@ class Grid(val width: Int, val height: Int, val tiles: Array<Tile>) {
         }
     }
 
+    /**
+     * Mark the tile at the given coordinates as flagged.
+     *
+     * @throws IllegalArgumentException if the X coordinate is outside
+     * the range of [0, width), or if the Y coordinate is outside the
+     *  range of [0, height).
+     */
+    fun flag(x: Int, y: Int) {
+        if (!valid(x, y) || !this[x, y].masked) {
+            return;
+        }
+
+        with (this[x, y]) {
+            place(x, y, copy(flagged = true))
+        }
+    }
+
     override fun toString(): String = buildString {
         for (y in 0 until height) {
             for (x in 0 until width) {