fix(backlinks): keep truncateMiddle within maxLength (#134)

src/client/features/backlinks/backlinksPageUtils.test.ts

@@ -0,0 +1,33 @@
+import { describe, expect, it } from "vitest";
+import { truncateMiddle } from "./backlinksPageUtils";
+
+describe("truncateMiddle", () => {
+  it("returns the value unchanged when it already fits", () => {
+    expect(truncateMiddle("short", 10)).toBe("short");
+    expect(truncateMiddle("exactly-ten", "exactly-ten".length)).toBe(
+      "exactly-ten",
+    );
+  });
+
+  it("never returns a string longer than maxLength", () => {
+    const value = "/very/long/path/segment/that/keeps/going/here";
+    for (let maxLength = 0; maxLength <= value.length; maxLength++) {
+      expect(truncateMiddle(value, maxLength).length).toBeLessThanOrEqual(
+        maxLength,
+      );
+    }
+  });
+
+  it("keeps head and tail around a middle ellipsis", () => {
+    expect(truncateMiddle("abcdefghijklmno", 10)).toBe("abc...mno");
+    expect(truncateMiddle("/very/long/path/segment/here", 12)).toBe(
+      "/ver...here",
+    );
+  });
+
+  it("head-truncates when there is no room for both sides", () => {
+    expect(truncateMiddle("abcdefgh", 4)).toBe("a...");
+    expect(truncateMiddle("abcdefgh", 3)).toBe("abc");
+    expect(truncateMiddle("abcdefgh", 2)).toBe("ab");
+  });
+});

src/client/features/backlinks/backlinksPageUtils.ts

@@ -114,8 +114,15 @@ export function extractUrlPath(url: string) {
   }
 }
 
+const ELLIPSIS = "...";
+
 export function truncateMiddle(value: string, maxLength: number) {
   if (value.length <= maxLength) return value;
-  const sideLength = Math.floor((maxLength - 1) / 2);
-  return `${value.slice(0, sideLength)}...${value.slice(-sideLength)}`;
+  if (maxLength <= ELLIPSIS.length)
+    return value.slice(0, Math.max(maxLength, 0));
+  const sideLength = Math.floor((maxLength - ELLIPSIS.length) / 2);
+  if (sideLength <= 0) {
+    return `${value.slice(0, maxLength - ELLIPSIS.length)}${ELLIPSIS}`;
+  }
+  return `${value.slice(0, sideLength)}${ELLIPSIS}${value.slice(-sideLength)}`;
 }