Do not allow picking cells twice

src/game/Game.ts

@@ -76,10 +76,21 @@ interface Sequence {
     numberOfFulfilled: number
 }
 
+interface Buffer {
+    value: string
+    positionInMatrixRow: number
+    positionInMatrixColumn: number
+}
+
+interface Cell {
+    value: string
+    isUsed: boolean
+}
+
 export class Game {
     state: State = {selectionMode: SelectionMode.FreePick}
     public readonly size: number
-    public readonly buffer: string[] = []
+    public readonly buffer: Buffer[] = []
     private readonly timeoutInterval: ReturnType<typeof setTimeout>
     private readonly startTimeTimeStamp: number
     private endTimestamp: number | null = null
@@ -106,8 +117,14 @@ export class Game {
         return this.timeout - (Date.now() - this.startTimeTimeStamp)
     }
 
-    getCell(row: number, column: number): string {
-        return this.matrix[row + column * this.size]
+    getCell(row: number, column: number): Cell {
+        return {
+            value: this.matrix[row + column * this.size],
+            isUsed: this.buffer.some(x =>
+                x.positionInMatrixRow == row &&
+                x.positionInMatrixColumn == column
+                ),
+        }
     }
 
     getSequences(): Sequence[] {
@@ -116,7 +133,7 @@ export class Game {
             for (let i = 0; i < this.buffer.length; ++i) {
                 let prefixLength = 0;
                 for (let j = 0; j < Math.min(sequence.length, this.buffer.length - i); ++j) {
-                    if (this.buffer[i + j] != sequence[j]) {
+                    if (this.buffer[i + j].value != sequence[j]) {
                         // abort sequence
                         prefixLength = 0
                         break;
@@ -160,7 +177,16 @@ export class Game {
             Won: () => {throw new IllegalMoveError()},
             Lost: () => {throw new IllegalMoveError()},
             InProgress: (selectionMode) => {
-                this.buffer.push(this.getCell(row, column))
+                const cell = this.getCell(row, column)
+                if (cell.isUsed) {
+                    throw new IllegalMoveError()
+                }
+
+                this.buffer.push({
+                    value: cell.value,
+                    positionInMatrixRow: row,
+                    positionInMatrixColumn: column,
+                })
 
                 matchSelectionState({
                     Free: () => {