feat(createCharacterComparison): add generic for font type and checks for the absence of the fonts

src/shared/lib/helpers/createCharacterComparison/createCharacterComparison.svelte.ts

@@ -15,16 +15,22 @@ export interface LineData {
  * @param fontB - The second font definition
  * @returns Object with reactive state (lines, containerWidth) and methods (breakIntoLines, getCharState)
  */
-export function createCharacterComparison(
+export function createCharacterComparison<
+    T extends { name: string; id: string } | undefined = undefined,
+>(
     text: () => string,
-    fontA: () => { name: string; id: string },
-    fontB: () => { name: string; id: string },
+    fontA: () => T,
+    fontB: () => T,
     weight: () => number,
     size: () => number,
 ) {
     let lines = $state<LineData[]>([]);
     let containerWidth = $state(0);
 
+    function fontDefined<T extends { name: string; id: string }>(font: T | undefined): font is T {
+        return font !== undefined;
+    }
+
     /**
      * Measures text width using a canvas context.
      * @param ctx - Canvas rendering context
@@ -36,10 +42,11 @@ export function createCharacterComparison(
     function measureText(
         ctx: CanvasRenderingContext2D,
         text: string,
-        fontFamily: string,
         fontSize: number,
         fontWeight: number,
+        fontFamily?: string,
     ): number {
+        if (!fontFamily) return 0;
         ctx.font = `${fontWeight} ${fontSize}px ${fontFamily}`;
         return ctx.measureText(text).width;
     }
@@ -73,7 +80,7 @@ export function createCharacterComparison(
         container: HTMLElement | undefined,
         measureCanvas: HTMLCanvasElement | undefined,
     ) {
-        if (!container || !measureCanvas) return;
+        if (!container || !measureCanvas || !fontA() || !fontB()) return;
 
         const rect = container.getBoundingClientRect();
         containerWidth = rect.width;
@@ -92,22 +99,24 @@ export function createCharacterComparison(
         let currentLineWords: string[] = [];
 
         function pushLine(words: string[]) {
-            if (words.length === 0) return;
+            if (words.length === 0 || !fontDefined(fontA()) || !fontDefined(fontB())) {
+                return;
+            }
             const lineText = words.join(' ');
             // Measure both fonts at the CURRENT weight
             const widthA = measureText(
                 ctx!,
                 lineText,
-                fontA().name,
                 Math.min(fontSize, controlledFontSize),
                 currentWeight,
+                fontA()?.name,
             );
             const widthB = measureText(
                 ctx!,
                 lineText,
-                fontB().name,
                 Math.min(fontSize, controlledFontSize),
                 currentWeight,
+                fontB()?.name,
             );
             const maxWidth = Math.max(widthA, widthB);
             newLines.push({ text: lineText, width: maxWidth });
@@ -121,16 +130,16 @@ export function createCharacterComparison(
             const widthA = measureText(
                 ctx,
                 testLine,
-                fontA().name,
                 Math.min(fontSize, controlledFontSize),
                 currentWeight,
+                fontA()?.name,
             );
             const widthB = measureText(
                 ctx,
                 testLine,
-                fontB().name,
                 Math.min(fontSize, controlledFontSize),
                 currentWeight,
+                fontB()?.name,
             );
             const maxWidth = Math.max(widthA, widthB);
             const isContainerOverflown = maxWidth > availableWidth;
@@ -155,16 +164,16 @@ export function createCharacterComparison(
                         const wA = measureText(
                             ctx,
                             testFragment,
-                            fontA().name,
                             fontSize,
                             currentWeight,
+                            fontA()?.name,
                         );
                         const wB = measureText(
                             ctx,
                             testFragment,
-                            fontB().name,
                             fontSize,
                             currentWeight,
+                            fontB()?.name,
                         );
 
                         if (Math.max(wA, wB) <= availableWidth) {