Fixed amount calculations

src/models/entities/DistanceDonation.ts

@@ -29,10 +29,17 @@ export class DistanceDonation extends Donation {
    * The exact implementation may differ for each type of donation.
    */
   @IsInt()
-  public get amount(): number {
+  public get amount() {
+    return this.getAmount();
+  }
+
+  /**
+   * The function that calculates the amount based on the runner object's distance.
+   */
+  public async getAmount(): Promise<number> {
     let calculatedAmount = -1;
     try {
-      calculatedAmount = this.amountPerDistance * this.runner.distance;
+      calculatedAmount = this.amountPerDistance * await this.runner.distance();
     } catch (error) {
       throw error;
     }