game: add: goal work

frontend/static/js/api/game/Segment.js

@@ -8,8 +8,32 @@ class Segment
      */
     constructor(start, stop)
     {
+        /**
+         * @type {Point}
+         */
         this.start = start === undefined ? new Point() : start;
+
+        /**
+         * @type {Point}
+         */
         this.stop = stop === undefined ? new Point() : stop;
+
+    }
+
+    angle()
+    {
+        let x = this.start.x - this.stop.x,
+            y = this.start.y - this.stop.y;
+
+        return Math.atan2(y, x);
+    }
+
+    len()
+    {
+        let x = this.start.x - this.stop.x,
+            y = this.start.y - this.stop.y;
+
+        return (x ** 2 + y ** 2) ** (1 / 2);
     }
 
     /**