utils: Add function to map card to its image name.

The function will be used during rendering the cards,
where we require the filenames of the images corresponding
to each variant of the UNO card.

backend/src/utils.ts

@@ -1,5 +1,6 @@
 import { Response } from 'express';
 import { AuthRequest } from './middlewares/authMiddleware';
+import { CardColor, UNOCard } from './types';
 
 export type ControllerFunction = (
     req: AuthRequest,
@@ -15,3 +16,43 @@ export function catchError(fn: ControllerFunction): ControllerFunction {
         }
     };
 }
+
+export function getCardImageName(card: UNOCard): string {
+    function getColorAbbreviation(color: CardColor): string {
+        switch (color) {
+            case 'red':
+                return 'r';
+            case 'blue':
+                return 'b';
+            case 'green':
+                return 'g';
+            case 'yellow':
+                return 'o';
+            default:
+                return '';
+        }
+    }
+    if (card.type === 'wild') {
+        if (card.value === 'colchange') {
+            return 'CC';
+        } else {
+            return 'P4';
+        }
+    } else if (card.type === 'special') {
+        let value;
+        switch (card.value) {
+            case 'skip':
+                value = 'r';
+                break;
+            case 'reverse':
+                value = 'x';
+                break;
+            case 'draw2':
+                value = 'p2';
+                break;
+        }
+        return `${getColorAbbreviation(card.color)}${value}`;
+    } else {
+        return `${getColorAbbreviation(card.color)}${card.value}`;
+    }
+}