CCM-11438 Update interpolate and tests

Author: nicki-nhs

frontend/src/__tests__/utils/interpolate.test.ts

@@ -1,30 +1,41 @@
 import { interpolate } from '@utils/interpolate';
 
 describe('interpolate', () => {
+  it('returns empty string if input is empty', () => {
+    expect(interpolate('', { name: 'Test' })).toBe('');
+  });
+
+  it('returns the same string if no placeholders are present', () => {
+    expect(interpolate('No interpolation needed.', {})).toBe(
+      'No interpolation needed.'
+    );
+  });
+
   it('replaces simple variables', () => {
     expect(interpolate('Hello {{name}}!', { name: 'Test' })).toBe(
       'Hello Test!'
     );
   });
 
-  it('replaces plural based on value', () => {
+  it('removes variable if missing', () => {
+    expect(interpolate('Hello {{name}}!', {})).toBe('Hello !');
+  });
+
+  it('replaces plural based on numeric value', () => {
     expect(interpolate('{{count|item|items}}', { count: 1 })).toBe('item');
     expect(interpolate('{{count|item|items}}', { count: 3 })).toBe('items');
   });
 
-  it('replaces variable and plural in same string', () => {
+  it('falls back to plural if variable is not a number', () => {
+    expect(interpolate('{{count|item|items}}', { count: 'abc' })).toBe('items');
+  });
+
+  it('replaces variable and plural in the same string', () => {
     expect(interpolate('{{count}} {{count|item|items}}', { count: 2 })).toBe(
       '2 items'
     );
-  });
-
-  it('removes variable if missing', () => {
-    expect(interpolate('Hello {{name}}!', {})).toBe('Hello !');
-  });
-
-  it('falls back to plural if count is invalid', () => {
-    expect(interpolate('{{count|item|items}}', { count: 'not-a-number' })).toBe(
-      'items'
+    expect(interpolate('{{count}} {{count|item|items}}', { count: 1 })).toBe(
+      '1 item'
     );
   });
 
@@ -36,4 +47,13 @@ describe('interpolate', () => {
       )
     ).toBe('2 characters as 1 text message');
   });
+
+  it('handles missing variables by not including them', () => {
+    expect(
+      interpolate(
+        '{{characters}} {{characters|character|characters}} and {{missing}} {{missing|apple|apples}}',
+        { characters: 1 }
+      )
+    ).toBe('1 character and  apples');
+  });
 });

frontend/src/utils/interpolate.ts

@@ -6,47 +6,30 @@
  * - pluralisation: `{{variable|singular|plural}}`
  *
  * Example:
- * ```ts
  * interpolate('Hello {{name}}, you have {{count}} {{count|message|messages}}.', {
  *   name: 'John',
  *   count: 2,
- * });
- * // => 'Hello John, you have 2 messages.'
- *
- * interpolate('Hello {{name}}, you have {{count}} {{count|message|messages}}.', {
- *   name: 'John',
- *   count: 1,
- * });
- * // => 'Hello John, you have 1 message.'
- * ```
- *
- * @param template - The string containing `{{...}}` placeholders
- * @param variables - An object of variables
- * @returns The interpolated string
+ * }); // => 'Hello John, you have 2 messages.'
  */
 
 // eslint-disable-next-line security/detect-unsafe-regex, sonarjs/slow-regex
-const interpolationPattern = /{{\s*([^|}]+)(?:\|([^|}]+)\|([^}]+))?\s*}}/g;
+const interpolationPattern = /{{([^|}]+)(?:\|([^|}]+)\|([^}]+))?}}/g;
 
 export function interpolate(
   template: string,
   variables: Record<string, string | number> = {}
 ): string {
   // eslint-disable-next-line unicorn/prefer-string-replace-all
-  return template.replace(
-    interpolationPattern,
-    (_match, variable, singular, plural) => {
-      const key = variable.trim();
-      const value = variables[key];
-
-      if (singular !== undefined && plural !== undefined) {
-        const count = Number(value);
+  return template.replace(interpolationPattern, (_, key, singular, plural) => {
+    const value = variables[key];
 
-        if (Number.isNaN(count)) return plural;
-        return count === 1 ? singular : plural;
-      }
+    if (singular !== undefined && plural !== undefined) {
+      const numeric = Number(value);
 
-      return value == null ? '' : String(value);
+      if (Number.isNaN(numeric)) return plural;
+      return numeric === 1 ? singular : plural;
     }
-  );
+
+    return value == null ? '' : String(value);
+  });
 }