Implement move squares highlighting

Issue #3

frontend/visuals.js

@@ -89,12 +89,27 @@ export function rowColToBoardIndex(row, col) {
 export class ActiveSquares {
   constructor() {
     this.selectedSquare = null;
+    this.moveSquares = [];
   }
   selectSquare(canvas, position) {
     let [r, c] = boardIndexToRowCol(position);
     canvas.drawSquareColor("#c0c0ff", r, c);
     this.selectedSquare = position;
   }
+  setMoveSquares(canvas, moveSquares) {
+    moveSquares.forEach((position) => {
+      let [r, c] = boardIndexToRowCol(position);
+      canvas.drawSquareColor("#ffffc0", r, c);
+      this.moveSquares.push(position);
+    });
+  }
+  unsetMoveSquares(canvas) {
+    this.moveSquares.forEach((position) => {
+      let [r, c] = boardIndexToRowCol(position);
+      canvas.drawSquareColor(canvas.decideColor(r, c), r, c);
+    });
+    this.moveSquares = [];
+  }
   unselectSquare(canvas) {
     if (this.selectedSquare === null) return;
     let [r, c] = boardIndexToRowCol(this.selectedSquare);